THESIS. BACTERIOLOGY OF THE SOIL. DW. €, Barnum, 1896. : kes anlar ke wcieldeamcade Fs y ee LR RA A Re A | cA RRA A [Ahh A RA AMAA AMAA A AAP ICHIGAN STATE UNIVERSITY LIBRARIES am mi 0163142 , 3 1293 00627 1005 LIBRARY | Michigan State niversity pe PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES retum on or before date due. DATE DUE DATEDUE DATE DUE jL-/ea4ues MSU Is An Affirmative Action/E qual Opportunity Institution c:\cire’ \datedue.pm3-p. 1 -- T-H-E-S-I1I-S8S &- on -: B-A-C-T-E-R-I-0-L-0-G-Y O-F T-H-E S-O0-I-L :- f - | é ° Wy Wi T. Barnum. -__ Au;;ust 13th, 1696. -1- BACTERIOLOGY OF THE SOIL. The giving of students of this college an opportun- ity to pursue the study of bacteriology, clearly shows tnat the subject is gaining a place of equal importance as the other sciences. It has been but little more than a decade since the subject has been considered of much importance, but in that time its rapid developement and its recognized impor- _ tance seem to have overwhelmed the slower progress of the other sciences. The confidence placed in hbactcriology seems to be fully justified. It has already accomplished much, but mo can be expected from it. In the medical world it has explai ed many mysteries. The cause of many diseases can now be pointed out. It has also been shown that bacteriology is intim- ately connected with agriculture, and it is in this connec- ticn thet we are most interested in it. It has been shown that the oxidation and reduction which takes place in nature --- such as the resolution of dead animal and vegetable matter, the breaking up of nitrogenous materials into the nitrates, the specific fermentation so important in articles of diet, and the many other purposes--- are caused by the growth of microbes. We can not appreciate the importance 93859 of bacteria on the farm. Until recently some of us never thought of the farm as being stocked with bacteria, but they are there. They are in the wells, the brooks, and the rivers, in the milk,the butter, and the cheese; and in the soll, the air, and the compost heap. Among most people bacteria are looked upon as some- thing to be dreaded. The reason for this seems to be that the earliest investigations showed that bacteria caused dis- ease. While it is true that certain bacteria cause disease, it is equally true that other bacteria are of great benefit to us. Take for example the changing of cider to vinegar. The cider contains alcohol and to become vinegar it must be converted into acetic acid by taking up oxygen. This is done by the growth of bacteria (mother of vinegar.) The bacteria in some way take the oxygen from the air and gives it to the alcohol. Again, it is to bacteria that the farmer owes that article of food produced by the silo. If the correct bac- teria growth is secured, the ensilage will become a very desirable article of food for stock. The butter-maker owes something to bacteria. They act as decomposing agents. As a result of this decomposit- lon of the cream, products are produced, which at first have @ pleasant odor and t:ste. If ti:e cream is churned at tnis period tne butter becomes flavored with ¢ cse products of decomposition. The lfavor is the aroma of food butter and it is the eift of bacteria. In cheese making it bacteria that breaks down the casin and create products of a pleasant taste, without which the cneese would te worthless. A tree falls to the sound and the trunk becomes softened into a mass of brown powder which after a time Sinks into the ,jound and dissapears. A bird dies, after a time tiie flesh underjoes putrefaction, cases are given off, and the rest sinks into the sournd and dissnpears. Tt is foroush the ‘mency of bacterial orsanisms that the tree dissapears and tnat tne ticsues of the hird are decomposed. It is throush their agency that the soil is inriched and the continuance of life rendered possible. An organism of snecial importance, because of its power to enrich tne soil, is the, "nitrifying organism." Plants can not feed uron such thinss as albumen. They must have nitrates. The "nitrifying organism" converts the album enous comrounds into nitrates by further decomposition, which the ordinary putrefyinzs perms will not accomplish. Then toq it is through bacteria thnt certain plants are able to derive nitrogen from the air. By the rrowtn of these bactcria we may hope for a continuance of the supply of nitrogen to the soil. Theremin nt be mentioned other processes that would show the benefit of the growth of bacteria to man, »ut these are sufficient to show some of the thinzs that bacteria do and that they are not altorether producers of evil. Definition. Bacteria may he defined as sin.:-le celled microscop- is plants, living on hisher organisms. Classification. Bacteria are classificd as to form into: micrococcus or spherical bacillus | or rod-shaped spirillum Or screw-shaped as to action into patho;enic or disease producing. non-pathorenic or not disease producing. Multiplication. The principal way in which germs multiply is by division. The cell hecomes elonrated and then divides into two by a transverse croove. The two parts may separate or remain torether. Bacteria under certain conditions con- tains spores. These possess a greater power of resistance than the gurm. Tie spores are freed by the destruction of the cell and, under favorable conditions, they again produce bacteria. Movement. Some bacteria herve the power to move about in liquids. This is done by tne developement of whip-like appendages wiich, by their vibrations, propel the ferm. Action of Microbes upon Media. Media are the materials in which the microbes are grown. In general, the microbes reduce the media into its lnor;;anic compounds. In gelatin the microbes may rapidly liquefy it, as a result of the developement of soluahble fer- ments; they may slowly liquefy it; or they may not grow in selatin at all. The same may be true of azar. Identification of Germs. Germs may be identified by watching they action in the different media. Observe whether or not they liqu- ify gelatin; coagulate milk; grow exposed to air; are path- ozenic or non-patho;enic; and whether or not they produce gases, acids, alkalies, colors, spores, o@ors, or phosphor- esence. Also notice the temperature at which they crow, rapidity of growth, action of the anilin dyes upon them, and the form of growth in the media. These observations app- lies to the description of the germ and its characteristics, as given by the text-book, will enable the worker to make the identification . How germs were srown. As cultrure media, galatin was first used. Tt wes mde by boiling 500g. of chopped lean beef in 1000C.C. of water, for 15 minutes. This miterial was then filtered and to the filtrate then was added 100g. of gelatin, 10 fg. of dry peptone, and 5 g. of common salt. This mixture was then ‘“eated in a water bath and filtered. The solution was then made neutral and nearly clear. Twenty-five ster- jlized test-tubes were then filled to a depth of about 1 uf inches. The gelatin hardened upon coolins. A sample of rond dust was then procured. It was pulverized and 5 c. of it weighed out. Tne gelatin in one of the test tubes was then melted by steam heat. When suf- ficiently cooled, but still liquid, the 5 c. of soil was poured in, this inoculated the gelatin. An "Esmarch Roll- tube Culture," was then made of the inoculated gelatin by rotating the tube in a nearly horizontal position under a Stream of cold water. This solidified the gelatin ina thin itayer over the inside of the tube. This was placed in a cool place for developement. In 48 hours colonies were deveolped, but the hot weather melted the gelatin and no results were obtained. With another sample of soil, from the freshly plow- ed garden, another test-tube of fselatin was inocultaed,. With this a "Petri-dish Culture" was made by pouring the contents of te test-tube into a sterilized petri-dish. The gelatin was solidified by placing the dish into a very shallow current of water. In 48 hours colonies had devel- Oped. The surface of the selatin apnveared pitted. From above many of tne colonies were white, circular in form, and had entire edges. By the aid of the "Colony Counter" it was estimated th:t tnere were from 6,000 to 7,000 colonics srowing. Each colony is said to represent one zerm, so there must have bcen six or seven thousand germs in the 5 c. of soil. An examination of these colonies was made by the aid of the microscope. In order to bring out the shape of t’:e microbes more distinctly,"Simple Stains"of them were made This was done by the use of the anilin dyes, centian violet being a favorite. Several different examinations of these colonies were made and it was found tnere were diffcrent kinds of germs present. One moment showed a fine exhibit of micrococcus. Three others showed bacilli, two of which were much alike. The others grew in the form of long bending threads. During the next 24 hours this gelatin was liquified by the srowth of the ferms. Pure cultures of these germs were not made. Gelatin is not a satisfactory media to work with during hot weather.