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A STUDY OF THE GERMICEDAL
VALL-E OF ULTRA WOLET LECHT
PARTICULARLY THAT
PRODUCED BY THE. STERILAMP”

Thesis for the Degree of M. S.

MiCHIGAN STATE COLLEGE
Virginia L. Ross
1938

 

"A. Study of the

Germicidal Value of Ultra

Violet Light Particularly that

Produced by the Sterilamp."

WA STUDY OF THE GERMICIDAL VALUE

or ULTRA VIOLET LIGHTIJPARTICUIARLY THAT

PRODUCED BY THE STERILAMP.I

Thesis

Submitted to the Faculty of Michigan.State College
of Agriculture and Applied Science in partial
fulfillment of the requirements for the

degree of Master of Science

Virginia.Lucille Ross

June, 1938

TH E515

('\

A0213 754:9 GEE-31'1”

The writer desires to express grateful
acknowledgement of the valuable assistance
of Doctor W. L. Hallmann, Associate Professor
of Bacteriology,'under whom this work was
carried out, and of other members of the
Faculty of the Department of Bacteriology

and Hygiene of Michigan State College.

115928

TABLE OF CONTENTS

Title
Acknowledgement
1. Introduction
II. Historical
III. Experimental
A. The bactericidal and fungicidal powers
of the Sterilamp
B. Action of the Sterilamp on media
C. Practical limits of time and distance
on the bactericidal power of emanations
from a Sterilamp
D. Penetrability of various mediums to the
emanations of the Sterilamp with that
of a quarts tube
E. Comparison of the bactericidal power of
the Sterilamp and that of a quartz tube
IV. Summary and discussion

V. Literature cited

INTRODUCTION

 

The fact that light, particularly that portion of the
Spectrum known as ultra violet, exercises a definite germi-
cidal action has been known for many years, and much exper-
imentation has been carried on for the purpose of determin-
ing the exact nature and extent of this action, as well as
.to discover any possible practical applications. Recently
the possibilities inherent in ultra violet radiation have
been brought particularly to the notice of both the bacter-
iologist and the general public by the appearance of the
"Sterilamp", an ultra violet ray tube manufactured by the
Westinghouse Lamp Company.

Broad claims have been made concerning the abilities
of the Sterilamp with.particular reference to its use com-
mercially as a sterilizing agent, suggested uses ranging
from the purification of air to the preservation of food.

he object of this study was the determination of the actual
bactericidal value of the Sterilamp and the formation of a
theoretical foundation upon which to base a conception of

its practical value.

-1-
Historical

The term "ultraéviolet" includes a fairly wide band of the
spectrum; so, since the announcement of Downes and Blunt (18)
in 1877 that ultra-violet would kill the bacteria present in
decaying vegetable matter, investigators have attempted in the
interest of a higher level of efficiency to narrow this range
to certain specific wave lengths as proving most bactericidal.
The first, and simplest, conception was that of Hertel (17)
(1905) concurred with by Coblentz and Fulton (9) (192%) and by
Bayne-Jones (3) (1923), that the bactericidal power of ultra;
violet rays increased progressively as the wave length decreased
down to 1850 Angstrom units, with the stipulation that the pene-
trating power of the wave lengths below 1600 Angstrum units is
so slight that the rays may not pass into the bacteria far enough
to have much effect.

However, the results obtained by other investigators do
not support this theory. In 1917, H. S. Newcomer (23), work-
ing the typhoid fever organism found that the wave band range
between 2M35 and 26HO Angstrom units was the most effective.
Browning and Russ (l6) (1917~18), using agar surface culiures,
a tungsten lamp, and a quartz spectrometer, give a maximum of
2500 to 25h0 Anstrom units. Cernovodeanu and Henri (8) (1910),
using a.Cooper-Hewitt lamp and bacterial emulsions, found a
maximum at about 2800 Anstrom units. Mashimo (21) using agar
surface cultures and a quartz spectrometer, found a maximum at
2750 Angstrom units. Band (21), working with bactericidal rays

in the spectrum of the carbon arc lamp, showed that there were~

two maxima: the first from 3600 to 3M00 Angstrom units; and

the second from 3000 to 2000 Angstrom units, with the greatest
point of destruction of the two resting at 2500 Angstrom units.
Gates (15) (1930), using measured monochromatic energy found a
striking maximum between 2600 and 2700 Angstrom units. gar
and Hollaender (11) in 193M and later Dreyfer and Campbell-
Renton (10) in 1936 confirmed the maximum found by Gates. Duggar
and Hollaender (11) used various wave lengths between the limits
of 2537 and 6120 Angstrom units and found that in general the
maximum lethal effect was at 2652 Angstrom units when using

Bacillus megatherium, Bacillus subtilis, and Serratia marcescens

 

 

 

as test organisms, although the spores of Bacillus megatherium

 

exhibited a greater sensitivity to a wave length of 289” Angstrom
units. In the experiment of Dreyfer and Campbell-Benton (10)
organisms were again exposed to varying wave lengths of light.
The bactericidal effect varied with the orga.ism exposed, but in
all cases the line 2655 Angstroms was most effective, followed in
order by the lines 2536, 280M, 2MS3, and 2700 Angstroms.

Other factors concerned in the bactericidal effectiveness of
ultrapviolet radiation have been the subjects of investigation.
Dreyfer and Campbell-Benton (10) showed through reducing the in-
tensity of light by screening that the time required for a given
bactericidal effect was inversely preportional to the intensity
of the light. Bachem and Dushhin (1) (1933) exposed Serratia

marcescens to ultrapviolet rays of varying intensity and for

 

varying leng he of time and obtained results confirming these,

as long as the sensitivity of the bacteria to ultranviolet re-

-4-

mained constant. However, they found that this sensitivity in-
creased rapidly for the first two hours after plating, then after
reaching a'broad maximum, decreased sharply up to ten hours. Henri
and Cernovodeanu (8) (1910) observed that the germicidal action of
the ultrapviolet rays deceased more rapidly than the inverse square
of the distance from the source.

Henri (8) also noted that different mibrobes varied in their
sensitiveness. Duggar and Hollaender (11) found that the level of
energy required to kill bacteria was far below that necessary for
any effect on the vine of tobacco mosaic; while the level of
energy required to give any particular survivtor value was greater
for spores than for vegetative cells, and the resistance of the

spores of Bacillus megatherium was greater than that of Bacillus

 

subtitlis.

There has been much conflicting-data presented as to the
action of ultrapviolet radiation on yeasts. Presenting data on
one side of the question are Ieuer and Tanner (13) (1920), who
found that yeast cells could live only a few seconds to a few
minutes longer than bacteria when a very thin layer of a water
suspension was exposed at a distance of twentybfive cm from the
source of ultra—violet; Buchta (7) (1911+), who found that _s_§._o_cp_-

oromyces cerevisiae and Saccharomyces ludwigii could not survive

 

 

more than three minutes exposure to ultrapvioletzp Maurain and
Warcollier (20) (1909), who found that ultrapviolet would com-
pletely arrest fermentation in cider which was exposed in a very
thin layer; Schnitzler and Henri (26) (1910), who obtained an

inhibition of the acetic acid fermentation of wine by'ultrapviolet

radiation; and Lanzillotta (18) (1920), who found that an exposure
of twenty minutes killed the cells. On the other hand De Fazi (12)
(1921) claimed that in hisexperiments he exposed brewer's yeast
for twelve hours to the ultra-violet rays from a 1200 candle power
lamp at a distance of twenty cm, and that not only was the yeast not
injured by this treatment, but that its fermentative activity was
actually increased. All of the bacteria in the yeast were destroyed
after a brief exposure. Lindner (21) (1923) found that the exposure
of yeasts under fermentation conditions favored activity of the yeasts,
but exposure of cells in a shallow layer of liquid was fatal, and
herein may lie the explanation.

Reports about molds are also conflicting. Some workers state
that they are killed by exposure to ultrapviolet radiation without
much, difficulty. Read (25) (193k) destroyed heavy infections of

Aspergillus, Penicillium, RhiZOpus, and Mucor on the surface of

 

loaves of bread in fortybfive seconds by means of lethal rays from
"C" carbons at a distance of eight inches. Read found that the
open Carbon lamps emitted a higher intensity of the shorter fungi-

cidal wave lengths than quartz-mercury lamps.

Experimental

A. The bactericidal and fungicidal powers of the Sterilamp.

The Sterilamp is an argon, neon and mercury vapor filled tube
producing rays of which approximately ninetybthree percent fall in
the ultrapviolet range while ninetyzone percent are 2537 Angstrom
units. It will be noted that this latter value coincides very
closely with the values found by-a majority of investigators to
be highly bactericidal, and by several, to produce the maximum
lethal effect. The lamp is the invention of Dr. Harvey C. Rent-
schler, Director of research of the Testinghouse Lamp Company,
and Dr. Hebert F. James of the same company. Drs. Rentschler and

James have reported that cultures of Eberthella typhi, exposed to

 

the emanations of the Sterilamp at a distance of four inches, were

killed in eight seconds, cultures of Staphlococci, in twenty-four

 

 

seconds, and cultures of Aspepgillus, in nineteen minutes. These
reported results, however, are not commensurate with the results

and suggested applications released in newspaper reports, which

give the lamp as killing bacteria in less than one second, instantly
sterilizing breaths and instantly killing the bacteria on any article
exposed to its emanations. The Sterilamp was reported as having been
tried and found effective in restaurants, bakeries for keeping food
sterile, manufacturing plants for both food and personal articles,
hen houses, dairies, and hogpens. Also used to keep down the danger' .
of infection in toilets. The lamp has been used in the Operating
rooms of three hospitals, Duke HOSpital at Durham, N.C., Mayo Clinic

at Rochester, Minn., and the New York Medical Center. Dr. Deryl

-7.-

Hart, surgeon-in-chief Of Duke Hospital at a meeting Of the American
Institute gave the results Of 800 Operations in air purified by the
ultra-violet light. He said the death rate in chest Operations was
cut from five and five-tenths per cent to two and.nine-tenths per
cent. Infections after hernia Operations were cut from three and
three-tenths per cent to zero.

The concentration of light at the wave length of 2537 Angstrom
units was reported to have produced a lamp which might be used
without danger to the eyes. Therefore, in the gathering Of data
for this paper, at first no protective device was used. It was
found, however, by several workers with the Sterilamp that exposure
of the eyes for more than a very few minutes to the emanations of
the lamp results in very badly inflammed eyes; so for the comple-
tion of the work, dark goggles were used which were so constructed
as to completely shield the eyes.

‘In these studies the tubes and transformers were furnished by
the Westinghouse Lamp Company and set up as they recommended.

In order to obtain as uniform an inoculum as possible through-
out the complete study the following steps were taken:

I. A twentyhfour hour culture of each organism grown in nutrient
broth was used.

2. This culture was uniformly diluted by placing one loopful
with a platinum wire lOOp four mm in diameter in ten cc. of nutrient
broth.

3. The diluted culture was smeared over the surface Of an area

of four square inches of an agar plate previously poured and allowed

to harden. This smear was made with a sterile cotton swab.

H. The smear was allowed to stand one-half hour at 37°C
before exposure to the Sterilamp so as to permit excess moisture
to evaporate and remove any possibility of the exercising Of a
protective influence by the broth in which the organisms were
suspended.

By removal of the petri dish cover the cultures so prepared
were exposed to the emanations of a single Sterilamp at a distance
of six cm ( 5 2mm) from the tube. (The fact that the cultures were
not exposed to any bactericidal action Of the emanations until the
cover was renoved is shown in table I) .A group of identically
prepared plates were Opened for equal periods of time without
exposure to the emanations from the Sterilamp, and these plates
were used as controls. All plates were incubated for twentysfour
hours at 37°C. As the colonies were largely confluent, it was
impossible to make exact counts, so the growth was recorded as
ranging from negative to four plus. Four plus growth was that
typical Of the control plates, two plus growth was approximately
one-half as dense; while one plus was defined as from ten to one

hundred discrete colonies and plus-minus, as less than ten.

Bactericidal
I. Unshielded lamp.

a. Non-spore-forming bacteria.

.A series of non-spore-forming bacteria of common occurrence
and representative nature were chosen as test organisms. These

were Staphylococcus aureus, Eberthella typhi, Escherichia coli,

 

 

 

Mycobacterium phlei, Pseudomonas aeruginosa and Aerobacter aerogenes.

 

-9.

The strains used were obtained from the stock cultures.

The time of exposure varied from five seconds to one minute.
There was a marked bactericidal effect from five seconds exposure
of all of these organisms, while fifteen seconds exposure reduced

the average count of each, with the exception of Mycobacterium phlei,

 

to less than ten. gchbacterium phlei appears slightly more resistant.

 

The differences in the average count Of these six bacteria at the
end of fifteen seconds exposure cannot be considered as particularly
significant, as it is practically impossible to Obtain exactly the
same number of organisms on each smear.

' b. Spore-forming bacteria.

(1) Bacillus subtilis and Bacillus mzpoides were selected
as test organisms, as well as an unidentified sporeéformer (x1),
isolated from a.plate previously exposed to the light. There was
no discernible bactericidal effect on any of the three organisms
from five seconds exposure. From fifteen seconds exposure there

was an appreciable lethal effect on Bacillus subtiles; while at

 

the end of thirty seconds exposure the plates showed only two plus

growth. The plates of Bacillus mycoides and (x1) were nearly ster—

 

ilized by thirty seconds exposure.
(2) To further demonstrate the effect of the presence of
spores on the bactericidal power of emanations from a Sterilamp, an

eight hour and a two months culture of Bacillus mycoides were exposed

 

to the unshielded Sterilamp for intervals of five, ten and fifteen
seconds. The cultures were examined microscopically prior to inocu-
lation, and the eight hour culture was found to be free from Spores,

while the two month culture contained 100 per cent spores. The

results indicate a greater resistance in the spore containing
culture, but show a marked bactericidal effect on this culture

at the end of fifteen seconds exposure. The reduction Obtained
was from the four plus growth of the control plates to two plus
growth, or a reduction of nearly one half in the number of Spores

which germinated.

II. Shielded lamp.

a. In a second series a variation was made in the technique
of exposure by the use of a device for the control Of the amount of
light emitted by the Sterilamp. The purpose of this device was to
make possible a.more equitable comparison of lamps of varying size
and consisted Of a metal shield in which there was a narrow Open—
ing (3mm wide and 35mm long) through which passed the rays from
the lamp. Control plates exposed under the shielded portion of the
lamp showed no diminution in growth, demonstrating the fact that
the metal was impermeable to the bactericidal rays and acted as an
effective shield. The distance from the lamp to the plate was
fifteen cm, and the periods of exposure were increased to from one
to seven minutes. Under these conditions an exposure Of two minutes
resulted in approximately the same degree of bactericidal action as
was effected by an exposure of five seconds to the unshielded light.

Eberthella typhi again appeared slightly less resistant to the rays

 

and Bacillus subtilis decidedly more resistant than.Escherichia coli

 

while Mycobacteriumgphlei did not show as great a relative resistance.

 

III. Dry plates.

To test the effectiveness of the Sterilamp on the bacteria

-I’-

when exposed on a dry glass surface, the same technique for
smearing was used as in I and II with the exception that the
smears were made and dried directly on the inner glass surface
of a sterile petri dish. The smears were then exposed to the
emanations of a shielded Sterilamp for intervals of from one to
seven minutes, nutrient agar was poured over the cultures, and
they were incubated at 37°C for twentyhfour hours. The results
showed no pronounced difference from those Obtained in II.

Staphyloccoccus aureus, Eberthella typhi, and Bacillus subtilus

 

 

appeared slightly more resistant when exposed on the dry glass.

Escherichia coli showed about the same degree of resistance as

 

when exposed on agar.

Fungicidal
I. Yeasts.
’0 cm! s ,
Bauer and Tannerap gmented yeaps to be more res1stant to
the action of ultrapviolet than White (13). 0f the three yeasts

selected, two Saccharomyces ellipsoideus and Saccharomyces cerevisiae,

 

 

are unpigmented, and the third, Torula rosea, produces a rose pig-
ment. The technique for exposing the yeasts was that described on
page seven with the exception of the replacement of nutrient agar

by dextrose agar, and the periods of exposure to the emanations of
the unshielded Sterilamp were five, ten and fifteen seconds. The
plates exposed for five and ten seconds showed a marked diminution

in growth; those exposed fifteen seconds a decrease of approximately
one half as compared to the control plate; and nearly all of the

organisms were destroyed when Saccharomyces cerevisiae was exposed

 

for thirty seconds. These results are comparable with those obtained

for the spore producing bacteria and there is no appreciable differ-

_/:..

ence between the effect on the unpigmented true yeasts, and the

pigmented false yeast.

II. Molds
The molds selected as being diversfied types and typical Of

the most common Offenders in food spoilage were Aspergillus niger,

 

Rhizgpus nigricans, Penicillium.italicum, Oospora lactis, and

 

two cultures isolated from eggs and known as X3 and X6. The pro-
cedure was changed slightly to conform with the difference in the
nature of the test organism. .

(l) A.three day Old culture grown on dextrose agar was used
so that the culture would be fully matured and contain both vegeta-
tive cells and fruiting bodies.

(2) The growth from the slant culture was suspended in sterile
saline. This suspension was smeared with a sterile cotton swab
over an area of four square inches on the inner surface of a sterile
petri dish, and allowed to dry at room temperature for one-half hour
before exposure to the rays Of the Sterilamp.

(3) After the molds were exposed tO the shielded Sterilamp,
dextrose agar was poured over the smears, and the plates were
allowed to incubate for twentybfour hours at room temperature.

As it was impossible to Obtain satisfactory growth of Oospora
lactis by this technique, this organism was spread on the surface
of an agar plate rather than on the dry glass surface and exposed
to the emanations from the unshielded Sterilamp. Table TI shows
that culture X3 and culture 16 were not effected by five minutes

exposure, and that thirty minutes exposure had only a slight effect

-l3—

on.Aspepgillus nigervand RhizOpus nigricans and none on Penicillium

 

 

 

italicum. Cultures of these organisms kept continuously irradiated
over a.period of eleven hours showed no signs of growth during Or
after this period of irradiation. The medium was moistened with
sterile saline to compensate for the loss of moisture during the
period, and half of the plates were reinoculated with the molds.

The newly inoculated plates grew well, demonstrating that the medium
was still suitable for growth.

Oospora lactis, which possesses a different type Of fruiting

 

body than the above molds, was shown to be less resistant to the
ultra-violet irradiation. Some effect was noted after fifteen
seconds exposure to the unshielded light; thirty seconds exposure
nearly sterilized the plates while sixty seconds exposure did
completely sterilize them. These results would show Oospora

lactis to possess about the same degree of resistance to the

Sterilamp as the spore-ferming bacteria.

-/y..

Table I. Bactericidal power of emanations of a
Sterilamp on organisms protected by a
petri dish cover.

 

 

 

 

 

Trig Unegposed as w t vs
1 1 4+ 4+
3 4+ 4+
3 4+ 4+
4 4+ 4+
Average 4+ 45+

./I.

Table II Bactericidal Power of Emanaticns from a
Sterilamp on organisms smeared on agar plates.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Trial 1 ime of ex osurme
o 1 17:125—- so 1 min
‘81
1 4+ + +
2 4+ + i (37‘ + 11?
3 1 4+ + + i: 3
‘ 4+ 3+ + i 9
5 4+ 2+ + t 9
Average 4+ 2+ 4- 4;
E. Typhi
1 W 4+ + 1 + * i“)
2 1 4+ + 1 + +
3 1 4+ + 1 1(6) t 1;
4 W 4+ + + + 1
5 7 4+ + 7 + {- 10}
7 4+ + - '1'. l
8 4+ + 1 ~ 32(2H ‘32 1
Average II- + t It __
Esch. 0011
1 4-!- l 1 c...“ 4.. .-
3 4+ 1 .. .. ..
3 4+ 1 - - --
4 4+ .. .. ..
5 4+ 1 3+1 - ..
6 4+ 3+ 1 -' -j
7 4+ 3+ + -'j
8 4+ + - -'
9 4+ 2+ +
10 4+ 2+ I 1‘10
11 4+ 3+ 4; 10
13 4a- 2+ W +
Ferage 4]. 2... i: ‘ .. .. .T

 

XNumber of colonies on plate.

 

 

 

 

 

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1 I 1% I 4+
2 I 4+ I 4+
3 I 4+ I 4+
4 I 4+ I 4+
5 I 4+ I 4+
6 I 4+ I 4+
7 4+ I 4+
8 4 5+ 5:
verage . 7E- In.
B. myccides
1 4+ 4»- i 3 ‘11. (1)
2 L 4+ I 4+ . 4.: 4 .-1
3 43- _ 41- r IE 6 -
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-’,..

Table III Effelt of presence of spores on the
bactericidal power of emanations from

 

 

 

    
 

 

 

 

 

 

 

 

 

a Sterilamp.
Til-51 me o osure inficonds

O 5 ___].§
1 I 4+ 4+ 2+ 7 + L 8 hr.cu1ture
3 4a» 3+ 3+ + ’
AL 4+ 3+ 8+ 4- '
Average 4+ 34- 2+ 4-
1 4+ 4+ 3+ I 2+ 2 mo. culture
2 J 4. l 4+ 3. J 2+ l
3 :4; 4+ 3+ 2+

r f I I I

Average 4.. 4+ , 3+ 3+ ,

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-/’-

Table IV Bactericidal Power of Emanation from a
Steril with a Controlled amount Of
light ob ained by passing the rays through
a narrow Opening on organism smeared on
surface of Agar Plates.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Trial Time of Ex ure in Minutes

0 .1- 2 I 3 4 5 6
1 4+ I Sprg‘ A age I + I I
2 4+ I 2"“ I + + I
3 4+ ‘ t ' i +
4 4+ I I -
5 4+ I 3+ 1+
6 Alt 3+ -_ la-
Average 4+ I 3+ ' + I at ‘1:

Eberthe typhi

1 4... + l 1(1)
2 4+ - l» I +, in)
3 l 4+ I l - - t 1 .
g t: ' * t "’ *
.6. 4:} 1(le -' 43
Average 4+ - t i: i 2':

"Number of colonies on plate.

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Table Iv

.10-

Cent. Bactericidal Power of lmanation from a
Sterilamp with a controlled amount of light
Obtained by passing the rays through a narrow
Opening on organisms smeared on surface of agar

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

plates.
Trial A Time of i osure in ginutes
O 1 2 g 4 5 6 A 7
lsIIheri Ihia CIli I I I
g 4* ~ I 4" I 3* I 3” I I I
3 | 4+ I I I I 3+ I + I+.(42III
4 I- 4+ I I I I + I + I- .
5 I I I I I I I
6 I 4+ I I I , I < +(37)
7 4* I I to)
3 I 4+ 4+ 3+ I 3+ , 3+ I
19 4-:- 44- 3+ I 2+ + I
0 4+ 4+ 3+ 2+ + I .
11 £1- 4» 3+ 3+ .+,, .
13 I 4+ I . I '-' I I
L3 4s» _ , ..
Average 49» 4+ 3+ . 2+ 3+ + t ;|:
nyco. Iphlei
g 3;; I I I iIi’I LEISI £151)
+ .. .-
4 4+ I "' - I
L _' it ' ‘-‘
Average I 4+ 4- «I; - -‘
B. subtilis (spores present) (24 hr. culture)
1 4+ 4+ 3+ I 3+ I I
3 I 4.4. I I. 3+ I I
4 4+ ~ I a 2+ I ' *
5 I 4-:- 3+ 2+ I I ,I
6 I 4+ R 4" I .I +
f? . 4+ «L
Average 4:- 4+ I 3+ + + +
xNumber of colonies on plate.

 

 

III 1.9.... I'."I'-I‘ "allt‘ 0"-..0’! I..." "!

.IIV“ 'l-'-lll-'.-l I.-"l ----. I‘"
1"...- "‘o".""' '.'l: a ‘i‘- -"-.
o
7.1!11‘ l'-"-"--00 ..--"‘ n-‘-' ---
II. $fll' I"-.$.-.1.I I! I. .'I. a :...1‘l|.. . II-..I u r r .o
.
i
.r. . I. I. ’3‘.-l..I.."-.’ +“.’l’ i ‘0"‘ ‘ie‘.
a
v
k
.0: II]. J Ll. lib".lvnll"ll..’ -“i-¥ ’1'.“ I...‘
I.
o!‘l| "O .3! {"9} .'I l’..' I .‘ri‘!’ ‘3’-.- -.lo-
I ..

32/-

Table V Relative bactericidal power of emanations

from unprotected Sterilamp and of a controlled
amount of light obtained by passing the rays
through a narrow Opening on Esch. oli.

 

Exposed 2 min

    

 

I Unexposed I mam 31w-

 

 

 

Trial with s it
I .
1 4+ I 2+ 2+
3 4+ I 2+ 3+
3 I 41- 3+ 3+
4+I- 3+ 8+

 

.g" I...

.22-

table VI. ‘Bactericidal Power of Enanation frcn.a Sterilamp with
a controlled amount of light obtained‘by‘passr:§_ths
rays through a narrow o ening- on organisns dri m
glass surface of petri shes.

 

 

 

 

 

 

 

 

 

 

 

 

1 II 4+ 4- ‘+
2 ‘; 4+ +I I,
i t f“ * II?
6 :I t: + :t
é
fwrageII'TI» + +
' EbertIh.
mm
1 4+ +
L
V'IESQT-%: I+
' Each»
coli
1 1+ 4+ ~+(1}I"' gzlg" :
‘733IB‘J 3: ;; 1;
Be nib-1'
. tilis
1 ‘+ 3+ .+
8 4+ 3+ 3+
3 4+ 3+
'IgsragpI%% gE?"F'Eh,

 

 

 

 

 

 

 

 

 

4617:... r... 3.; '- .4. a... any... .

”‘3‘

Table 711. Bactericidal Power of nuanations from a Sterilamp on
Yeasts Sneared on Agar Plates.

A.

 

 

 

_ 'r , M
Mr a
Torula roeea

Ia+ 2+ 2+
3+z+ 2.

 

 

fi++—%

Beech. e lipscideus

 

 

 

 

 

oueuma‘ gr...- 31...... g
I" I -
I
I
who.

 

 

 

 

 

 

 

 

a.

8+

2+

a .. ‘ -

3* i. 4; all"
1 +3

{Natalee If 0/»: 129.. 0» IA for

-ly-

Table VIII. Bactericidal Power of Emanations from a Sterilamp with
a controlled amount of light on molds dried on a
glass surface.

 

mu II...- gamma: if
' a I 39

 

 

 

 

 

Oul 'e 16
1 ~“I.
Tateraeo 341+

 

 

 

 

 

Oul pe 13
I z e
librage ‘iif %:
Asperfillus niger
1 4+ 3+
3 «4tl_ 3+
'Iverage 4+ 3;
Rhizopus nigricwls
I 4* l I a:
Wage % I 3:

Penicillium italimmm

1 2::
em. .

 

”t

 

 

 

-25-

Table II. Bactericidal Power of Emanations from a Sterilamp on
Oospora lactis spread on surface of agar plates.

 

 

 

 

 

 

 

 

 

T e in c 3
Trial I I'w
I __1.L___§2___,_92_,_1§9___1§h___
1 4+ 5 4+ 4+ I 3+ '-‘ I ‘-‘ *-‘
2 4+ 4+ 4+ 3+ '- x i,-_; -; .'_‘
3 4+ 4+ 4+ I 3+ .112) ._‘ j ,._. ..
mug. 4+I 1+ 4+ I *5; 4-. .. I ‘- ::

 

 

 

 

 

X Number of colonies on plate.

-1‘-

B. Action of the Sterilamp on media.
Browning and Russ (6) (1917) found that agar which has been
irradiated by ultrapviolet with a tungsten arc as source was not

inferior as a medium for the growth of Staphylococus aureus to

 

agar which had not been so irradiated. However, Coblentz and
Fulton (9) (192%) found that irradiation of agar by'ultra-violet

inhibited the growth of Escherichia coli on this medium and

 

Belford (2) (1927) corroborated this finding. Proks (2) (1933)
also reported that the irradiation of media makes it less suitable
for growth. Blank and Arnold (5) (1930) reported that the exposure
of any one of twenty carbohydrates and three carbohydrate deriva~
tives to rays of the wave length 2537 Angstrom units for periods
from one to five hours inhibited the growth of spores of Bacillus
subtilis when that carbohydrate was incorporated in the medium.
They also obtained similar results for agar and for agar-water
gels. Baumgartner (2) (1936) found that the irradiation of agar
gels or of sucrose sulution inhibited the growth of Bacillus

subtilis and of Escherichia coli if these substances were incor-

 

porated in the medium. Baumgartner reported that the irradiation
was accompanied by a marked production of acid, approximately one-
half of which was formic. When ten ml. of sterile nutrient agar
were exposed to ultrapviolet at a distance of five cm. from the
source for four hours, the pH drOpped from 7.2 to h.6. Neutraliza-
tion of this acid restored the ability of the culture to support
growth. Pratt (2M) (1936) irradiated agar with a Sterilamp at a

distance of four cm. for three to six hours and observed that three

-17..

hours irradiation had little effect on the growth of Bacillus
subtilis spores on this agar, but that six hours irradiation
almost entirely inhibited their growth. A mixture of spores and
vegetative cells would still grow on agar irradiated for eight

hours, and Escherichia coli, on agar irradiated for seven hours.

 

Irradiation of one per cent glucose solutions irradiated nine
hours by the Sterilamp drOpped in pH from 5.8 to less than 5.

It was necessary, therefore, to prove that the action of the
emanations was a direct one and was not due to changes produced
in the medium on which the organisms were placed. The effect
obtained from the exposure of organisms on glass surfaces served
as a partial control, but aside from this two types of control
experiments were run.

I. In the first of these, nutrient agar plates were exposed
to the emanations of a Sterilamp at a distance of six cm. for five

minutes and then inoculated in the usual way with Escherichia coli

 

or with Staphylococcus aureus. The same amount of growth was

 

obtained as was obtained on plates which had not been exposed.

2. Secondly, experiments were run to determine the effect of
exposure on the pH of the medium exposed. .A series of plates, each
containing fifteen cc. of nutrient agar, pH 6.7, were exposed at a
distance of six cm. At the end of five minutes and at the end of
thirty minutes plates were removed and the pH tested colorimetrically.
No change in pH was found.

Dextrose broth (initial pH 6.8) was exposed ( in 200 cc. amounts)
at a distance of six cm. and the pH tested at intervals. There was

no change in pH up to eight and one-half hours, but there was a drop

in pH to 6.65 at the end of thirty hours.

Table I. Bactericidal effect of agar eXposed to Sterilamp for
five minutes.

 

 

A ar inoculated Tgar Inoculated

    

 

 

 

 

Rial—J
l 4+ 4+ +
a 4+ 4+ all)“
3 4»- 4+ 1;.
Average 4» w 4-05 1.
Each. coli.
% 4+ 4+ -
4+ 4+ -f
3 40- 4» ‘-'
4 4+ 4+ I-I
Average ’ 4+ I!» 3-“

{Number of colonies on plate.

-19..

Table XL. Effect of emanations of a Sterilamp upon pH of agar.

 

 

 

 

 

 

Trial Time of mosure

___.Q _.nl__+5 n algae
l 6.7 6.7 6."?
2 6.7 6.”? 6.7

 

 

 

 

-30-

Table 111. Effect upon pH of dextrose broth of
irradiation by Sterilamp.

 

 

 

Wirradiation “Eff
:0: 67?
3% hours 6.8
8% hours 6.8
30 hours)! 6.65

—~

1* Experiment stapped at 30 hours due to marked growth
of bacteria in the broth.

-3]-

C. Practical limits of time and distance on the bactericidal
power of emanations from a Sterilamp.

If the Sterilamp is to be used in the practical fields which
have been suggested as possibilities,there should be some con-
ception of the distance over which it is an effective germicidal
agent and the time required for its action at varying distances.
Therefore plates were exposed at varying distances for five, ten,

fifteen and thirty minutes. The test organism used was Escherichia

 

gglié_and the plates were made as described on page seven. The
plates were arranged so as to be as nearly as possible in a position
vertical to the emanations of the lamp, and the distances were
measured from the center of the plate to the circumference of the
tube. It was found that if any article intervened between the lamp
and the plate in such a way as to cast a shadow over a portion of
the inoculated area on the plate, the bactericidal action on this
portion of plate was blocked out, and the shadow effect was evident
in the growth on the plate. So, evidently the bactericidal action v
of the Sterilamp, either through direct action of the emanations

or through a residual effect on the surrounding atmosphere possesses
no ability to turn corners.

At the end of five minutes exposure two out of three plates were
sterilized at a distance of nineteen inches; at the end of ten
minutes not more than one colony remained on any plate exposed at a
distance of twentyaseven inches; fifteen minutes exposure sterilized
three out of four plates at thirtyAfive inches, and thirty minutes
exposure sterilized four out of five plates at seventy—five inches.

The one plus growth appeared to be most consistent, so the distance

-32..

values at which this degree of growth was obtained were plotted
against the time necessary to obtain it.

In all probability, a battery of lamps would be necessary in
commercial use of the Sterilamp. Therefore, these experiments were
repeated using two lamps connected in series to determine the increase
in the 9%;fi2239- ratios. Distances were measured from the center of
the plate to a point midway between the two lamps. Not more than
two colonies deve10ped on any plate exposed for five minutes at a
distance of thirtybfive inches, and less than ten colonies deve10ped
on the plates exposed for ten minutes at fortyhfive inches and
fifteen minutes at eightyeone inches. Results shcwed a marked
increase in the distance over which a strong bactericidal effect

was obtained in a given time, but the bactericidal effectiveness

was not doubled by the use of two lamps.

_33—

100

80

 

Distan

in
60

inche

1+0

20

 

A A A

5 10 15 30
Time in minutes

 

EFFECT OF TIME AND DISTANCE ON BACTERICIDAL

POWER OF EMANATIONS OF THE STERILAMP

,A+ ONE LAMP

0 TWO LAMPS

-3‘y-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table XIII. Effect of time and distance on the bactericidal
power of the emanations of one Sterilamp ( as
shown) on Escherichia coli.

Distance 1 2 ' gnu 4 ’ 5
from 1m L
5 minutes exgosure
19 in. j .. j :(17' -..i
27 in. i j-JIOT +(15)* 1487'
35 in. i +(50)"' +(25)* 115?
Uneggosed ; 4+ r; 4+ 44:_
L . 10 minutes _eg._~gpeure
19 in. L 1(1) - ..
27 in. g 1|-_(1) £11) .-
35 in. L 1(2) 1(1) 1(1)
45 in. g H”) . +(30) +(38)
Unexgosed L 4-1: ; 4+ 4+
‘ L3 A J]_.I_5wminutes mute
19 in. . - - - -'
35 in. . t(1) - - -
45 in. ; 1(3) 1(3) 1X5)
62 in. I + + +
Unegposed L is- ; 4+ A 4+ 4+
___L _ L ' L Sojmigutes GXEOSIJIO
5 iv in. ‘ -‘ - -‘ - -
I? in. -’ - - - -
Esfi in. a - - 1(1) -
5 in. . - - g- + - -
93 in. I 147) 342) . 1(4) 510) -
115 in. 5+(37) +(16) +(20) +(25) +(34)
173 in. 1 2» 8+ L 2+ 2+ 8+
Qnexposed 'i 4L 4+ L_ 4+ ' 4+ 4&-

 

 

* ”an ‘er 4f :o/onl‘rJ a). [Xe/av

-353

Table XIV Effect of time and distance on the bactericidal
power of the emanations of two Sterilamps as shown
on Escherichia coli.

 

 

 

 

 

 

 

 

Trial
Distance from 1 2 3 u
lamp
5 minutes exposure
19 in. - - -
5 in. t - i- (2)”.
5 in. +(15) +(lh) +(29)
Unexposed h+ h+ h+
10 minutes exposure
19 in. 3(1) - '
27 in. :(h) z (2) -
as in. :( ) 3(1) -
5 in. :( ) t(6) 1(9)
62 in. gflzs) +(11) +(3h)
unexposed h+ 5+ N4
15 minutes exgosure
27 in. 't(l) - . -
33 111- 3(1) 2(2) - 1(1)
81 in. :(h) :(8) :(u) 1(3)
88 in. 2+ + 4
11% in. 2+ 2+ 2+ 24
unexposed h+ M+ ht hr

 

 

f/yam 6¢r of eo/nn'au or fi/afe.

-36..

D. Penetrability of various mediums to the emanations of the
Sterilamp.

.As ultra-violet irradiation has been a suggested means for the
sterilization of both milk and water, whole milk and saline were
two of the liquids selected for this study. The third, broth, was

selected as a clear liquid containing organic matter. Escherichia

 

ggli_was the test organism, and the cultures were prepared as on
page seven in deep culture dishes. The cultures were covered with
liquid to the desired depth and exposed for five minutes to the rays
of the Sterilamp, which was placed six cm. above the level of the
liquid. The liquid was carefully decanted, and the plates incubated
for twentyhfour hours at 37°C. Two sets of control plates were run
for each series, one which.was not exposed and one which was exposed
without a liquid covering.

There appeared a marked bactericidal effect through a thin
film of broth, and a noticeable one through a one mm. layer, but
-here penetration of the ultrapviolet rays appeared to stop. Through
whole milk there was found no evidence of any penetration. The rays
penetrated well through saline, however, sterilizing two out of four

plates which had been covered with saline to a depth of two cm.

-3 7..

Table IV Power of penetration of bactericidal emanations
from a Sterilamp through various mediums with
five minute emosure.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

W Dggth of broth
‘Oontro ' none ‘ thin film ' 2mm 1 3
l; I; a. + g I; %
a z: -' + :1: 2: a
4 4+ -‘ 4+ 4+ 4+ 4+
5 4+ - + 3+ 4+
6 4+ +(1Y‘ + 4+ 4+
7 4+ 4+ 4H-
8 4+ 44-
9 4+ 4+
10 4-1- 2+
11 4+ 3+
13 4|- 4+
13 4+ 4|-
lg 2: 4+
i‘verage 1+ - + 7% 4]. 4;;-
Depth of milk
1 4+ -‘ 4+ 4+
3 4H» - 4+ 4+
3 L 4i -’ 4i 4t
Average 4+ 2 r 4+ 4... '
Depth of saline
.Scm lom. 20m 30m 3.50m 40111
:21, 1': '1 F4 '1;
g 4H- - + 2'.’ 1 1(1) +
6 1: + +1
4 + .-
IVerage ‘4- -' - 1- t + _+

*Number of colonies on plate.

-3].

E. Comparison of the bactericidal power of the Sterilamp and
that of a quartz tube.

In order that a fair comparison of the two types of lamp,
which were very different in size, might be made, the amount of
light to which the plates were exposed was controlled by passing
the rays through the narrow Opening in the metal shield described
on page ten. Consequently the comparison is of the effectiveness
of the emanation from the same surface area of each lamp, and not

of each lamp as a complete unit. The organisms used were Escherichia

 

coli, Staphlococcus aureus, Eberthella typhi, Mycobacterium phlei,

 

and Bacillus subtilis, and upon three of these organisms there was

 

shown asslightly greater bactericidal effect by the quartz lamp
than by the Sterilamp. However, the Sterilamp demonstrated a

greater inhibitative effect upOn gycobacterium phlei than did the

 

quartz tube, and against Bacillus subtilis, the two lamps appeared

 

to have about the same degree of effectiveness.

In the spectra of the two lamps there is slightly more disper-
sion about some lines in the spectrum of the Sterilamp than about
the corresponding lines of the smaller tube, notibly about the most
intense line, that at 2537 Angstrom units. There is a.pronounced
band in both spectra at 2M85 Angstrom units and at 2655, and a
series of lines between 2810 and ESMO Angstrom units which are a
little more intense in the spectrum of the Sterilamp. The differences
are so slight, however, that the Spectra can be considered nearly
identical. Apparently the chief advantage of the Sterilamp would

lie in its much greater length.

-37..

The comparison of bactericidal effectiveness as carried out
in this experiment suggests a method of standardization of measure-
ment of the bactericidal power of ultrapviolet ray producing tubes,
using a standard tube as reference. The length of time required
to obtain either complete sterilization or a certain degree of
inhibition of growth by the emanations of a tube as compared to
the time required by the reference tube can easily be determined.
Accurate results can be obtained by preparing the plates carefully
according to a standard technique such as that described on.page
seven. By so controlling the amount of light, the bactericidal
effectiveness of the ultrapviolet radiation can be determined with-
out having as a variable the size and length of the tube.

Table XVI shows a comparison of three Sterilamps obtained in
this way. It will be noted that there is a greater variation in
results obtained for the same tube on different occasions than in
those obtained for the three lamps on the same trial. This might
be attributed to a difference in the density of the suspensions

used on different dates.

-yo—

 

 

 

 

 

 

 

 

Shield

A. Slit
3. Metal shield

O. Iboden support

-y/..

Table XVI Comparative bactericidal power of emanations

from a Sterilamp (l) and from a quartz tube (2)
with a controlled amount of light obtained by
passing the rays through a.narrow opening.

 

 

 

 

 

 

 

 

 

 

 

 

 

Lamp‘ Trial F TLme of ggposure in ginutgs
o 1 2 3 4 e ;-___
Esoh. coli
(1) 1 1T“ 3+
3 4+ 3+
3 4+ 4+ 3+ 3+ 1+
4 4+ 4+ 3+ 3+ +
5 4+ 4+ 3+ + +
6 4+ 4+ 3+
(3) 1 4+ +
3 4+ +
3 4+ 3+ + :51 + 5
g a a + £3
+ +
get 4:1- 21 o (a) 1'
mi}? 4» .4» a» 2+ 2+ +
(3) 4+ 2+ + + i i

1”Number of colonies on plate.

-y‘z-

Table XVI Continued

 

 

 

 

Lamp Trial Time of egposure in minutes
_ ap . gureus ' L

 

 

 

 

 

 

 

 

 

 

 

(1) d t +
+
a i 2:: .
Iver e
3%; 4* +‘
2 4+ -‘
E. typhi
(1) L :1. 2t.
(2) g 2: .1
Average .
(1) 4+ 1,
(2) 4» -‘
M100. h i
l 1 4+ i +
£23 A! 4+ LL, I 8+
Average ' 4+ '
2; 4+ 5+
p, subtilis
m a 2.: a
m L a: H a
Average ' ' ‘
$1; 4+ 3+
2 4+ 3+

p43...

 

 

 

'l'able XVII Comparison of three Sterilamps with a
controlled amount of light obtained by
passing the rays through a narrow opening
on organisms smeared on the surface of
agar plates.-

‘l‘ube Trial Time of e osure in minutes

0 3 4 L L 6

843 1 4+ 2».- + +

3 4+ 3+ + +
3 4* i: i r
876 1 L4». {8+ 5+
4+ 3+ +
3 4+ +
3 4+ +

937 1 4+ 4-

3 4+ + +

 

 

 

 

 

 

 

-yy;

Summary and Discussion
(A)

It was found that, in spite of claims to the contrary,
exposure of the eyes to the emanations of the Sterilamp for
more than a very few minutes caused a painful inflammation of
the eyes. Therefore, it is not advised that the Sterilamp be
used at any time unless the eyes are protected.

Of the non-spore-forming organisms exposed, no plate showed
more than ten colonies after fifteen seconds exposure to the

Sterilamp with the exception of Mycobacterium phlei, which

 

appeared slightly more resistant. Staphylococcus aureus was

 

killed in slightly less time and Eberthella typhi in a slightly

 

greater than that reported by Drs. Rentschler and James. The
instantaneous effects reported to the newspapers and popular
magazines were conspicuously absent.

White fifteen seconds exposure had an appreciable lethal
effect on spore-forming organisms, thirty seconds exposure was
necessary to obtain the same degree of killing obtained by
fifteen seconds exposure of non-spore-forming bacteria. .A

culture of Bacillus mycoides which contained spores was found

 

to be more resistant than one which did not.
The Sterilamp when partially shielded gave the same relative

results except with gycobacterium phlei, which did not show as

 

high a degree of resistance as formerly.
When the bacteria were exposed on dry plates, no marked

difference in results was obtained. Staphylococcus aureus,

 

E, tynhi, and B, subtilis were slightly more resistant; the

-y‘f.

results with.§, 32$} were approximately the same.

The results obtained from the exposure of yeasts were com-
parable to those obtained with spore-forming-bacteria. There
was a marked lethal effect at the end of ten seconds exposure, and
nearly all of the organisms were killed by thirty seconds exposure.
The pigmented yeast was not found to be more resistant than the
unpigmented.

Thirty minutes exposure was necessary to produce any lethal

effect on the molds exposed, with the exception of Oospo£a_lactis.

 

h
The extent of the lethal effect was very slight then altpugh this
is a much.longer period than that reported by Rentschler and James.
If the molds were irradiated continuously, mold growth was com-

pletely inhibited. Oospgra lactis showed about the same degree of

 

resistance as the spore-forming bacteria.

(3)

It was found that nutrient agar exposed to the unshielded
Sterilamp for five minutes was not inferior to unexposed agar
for the support of bacterial growth and that there was no change
in pH after one half hour's exposure. The pH of dextrose broth
was not affected by eight and one-half hour's exposure, but drapped
slightly at the end of thirty hours. These time periods were much
longer than.any periods of exposure in this work; so the bacterici-
dal effect must have been direct rather than because of any change

in the media.

(C)
The intervention of any article between the plate and the

lamp stopped bactericidal action; so there is apparently no

-6];-

residual effect of the emanations on the air surrounding the plate,
and any article to be sterilized should be in a direct line with
emanations from the Sterilamp without intervening objects. When
one Sterilamp was used, reduction to one plus growth was obtained
at thirtyefive inches on plates exposed five minutes, at fortybfive
inches after ten minutes, at sixtyetwo after fifteen minutes, and
at one hundred and fifteen after thirty minutes. The bactericidal
action obtained by the use of two lamps, connected in series, while

much greater, was not correspondingly twice as great.

(D)
Although many of the uses which have been suggested to the
public would presuppose some degree of penetration by the rays
of the Sterilamp into Opaque materials, this ability was not proven.
Through whole milk there was no evidence of any penetration; through
broth penetration stopped at one mm. Complete sterilization was

obtained, however, through saline with a depth of two cm.

(E)

In comparing the germicidal effect of the emanations of the
Sterilamp with those of a quartz tube, little difference was found.
The emanations from the same surface area of the quartz tube as of
the Sterilamp were more bactericidal for some organisms. The spectra
were nearly identical.

A.suggested method for controlling the amount of light to which
plates are exposed and for comparing ultra—violet ray producing tubes
is by means of a metal shield in which there is a small slit through
which the rays pass. With this at a given distance from the plate,

a standard method of preparing plates should be used. Much of the

confusion'because of varied results obtained by different workers

-y7v

is due to the variations in the technique of exposure.

10.

ll.

12.

_y{.

Literature Cited

Bachem, A and Dushkin, M.A.
Time factors concerned in the germicidal action of
ultrapviolet light.
Prat. 5“. 54,0. GJK and M04 30:700 073.!)

Baumgartner, J. G.
Ultrapviolet irradiated carbohydrates and bacterial growth.
Journ. Bact. 32: 75-77 (1936)

Bayne-Jones, S and Linden, J.S.
Bactericidal Action of ultrapviolet light.
Johns Hepkins 303p. Bull. 2:39 (1923)

Blank, I. H. and Arnold, W.
Action of radiation in the extreme ultrapviolet on B.subtilis
spores.
Journ. of Bact. 30:503 (1935)

Blank, 1.3. and Arnold W.
Inhibition of growth of B.subtilis by ultrapviolet
irradiated carbohydrates.
Journ. Bact. 30:50? (1930)

Browning and Russ
The Germicidal Action of Ultra~violet Radiation and
Its Correlation with Selective Absorption.
Proc. Royal Soc. London 90:33,(1917-18)

Buchta
Uber den Einfluss des Lichtes auf die sprossungder Hefe"
Cent. Bakt. Abt. M1 (II): juo (191M)

Cernovodeaunu, H andeenri, Mme. V.
Etude de 1'action des rayons ultraviolets sur les microbes.
Comptes rendus, October 151:72M,(l910)

Coblenta and Fulton
A radiometric investigation of the germicidal action of
ultrapviolet radiation.
Scientific Papers of the Bureau of Standards ##95 (192M)

Dreyfer, G. and Campbell, Benton
Proceedings of the Royal Society of London (series B)
Vol. 120: uu7-u72

Duggar, B. M, and Hollander, Am
Irradiation of plant vereises and of microorganisms with
monochromatic light, etc.
Journ. Bot. 27(3): 219—256 (193M)

DeFazi, Rm _
The action of ultrapviolet rays on the Saccaromycetes.
Journ. Ind. Eng. Chem. 13:265(1921)

13.

1h.

17.

18.

19.

20.

21.

22.

23.

eh.

I

-97..

Feuer and Tanner
Action of ultra~violet light on the yeast like fungi.
Journ. Ind. and Chem. Eng. 12(8): yuo-7u1 (1920)

Gates, F. L.
A study of the bact. action of ultra-violet light.
The absorption of ultrapviolet light by bacteria.
Journ. Gen. Physiol. 1M:32-h2 (1930)

Gates, F. L.
wave length and bacterial action.
Journ. of General Physiology 13:231-2h8 (1930)

. Gates, F. L.

The reaction of individual bacteria to irradiation
with ultrapviolet light.

501- 77(1997)= 350(1933)

Hertel, E.
Uber physiolog. Werkung von Strahlem verschiedener Lange.
Zeitschr. f. allg. Phys. 5:95 (1905)

Lanzillotta
Su11 uso dei raggi ultravioletti nella preparazione

dei vaccine. L
Ann. d Qgiene 30:2h5_25o (1920)

Laurens, H.
Physiological effects of radient energy.
Chem. Catalogue Co., N.Y. 1933

Maurain and Warcollies
Action des rayon ultraviolets sur lecidre enfermentation
Comp. Rend. Acad. Sci. 1h9:155-157 (1909)

Mayer, E.
Clinical application of sunlight and artificial radiation
Williams & Wilkins 00., Baltimore (1926)

Meier, F.
The Hicroscopic plant and animal world in ultrapviolet light.
An. Report of Smith. Inst. (1933)

Newcomer, H. S.
The Abiotic Action of Ultraviolet Light.
Journ. of Emp. Med. 26:shi,(1917)

Pratt, E. L.
The growth of microorganisms on media exposed to ultrap
violet radiations.
Journ. Bact. 32:613-619 (1936)

.5'0.

25. Read, J. W.
Destroying mold ppores on bread by'ultrapviolet radiation.
Cereal Chem. 11(1): 30-85 (193M)

26. Schnitzler and Henri
Die Werkungderultravioletten Strahlem auf die Essigsaurega—

rung des Weines
Biochem. Zeit. 25:263-271 (1910)

 

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