3l8 MICROBIOLOGY OF SOIL 



(Clostridium) paskurianus (or both), may come to the fore. The cleav- 

 age products then include alcohols, organic acids and carbon dioxide. 

 With B. {Clostridium) ffasteurianui butyric acid is one of the prominent 

 cleavage products. When combined nitrogen is also added to the 

 culture solution other organisms will develop prominently, notably 

 members of the subtilis group, butyric bacteria, aerogenes, etc. In the 

 soil itself the addition of sugar leads to a very marked increase in 

 number and, if acid production is favored, molds may subsequently 

 become prominent. In general it may be said that butyric, propionic, 

 acetic, formic and lactic acid, and ethyl, propyl, butyl and iso-butyl 

 alcohol are comnlon cleavage products. 



In the case of starch, pectins and pentosans, similar conditions hold 

 good. Diastatic enzymes seem to be produced by various bacteria, 

 as well, as molds and streptothrices. Members of the subtiUs group 

 and B. fluorescens seem to be able to transform starch into sugar with- 

 out difficulty. It needs hardly be added here that the vast quantities 

 of organic acids and of carbon dioxide thus formed must play an im- 

 portant r61e in the breaking down of the mineral constituents in the 

 soil. 



Fats and Waxes' 



Origin and DecotAposition. — Plant substances contain varying 

 proportions of fats and waxy materials. In the dry matter pf grasses 

 and cereal straw crude fat is usually present to the extent of 1.5 to 

 2.0 per cent. In hay made from clover and other legumes the proporr 

 tion of crude fat is rather more than 2 per cent. In cereal grains it 

 may range up to 4 or 5 per cent while in soy beans the content of 

 crude fat is 19 per cent, in germ oil meal 22 per cent and flax seed 

 meal 34 per cent. 



Under the influence of enzymes produced by molds, yeasts and 

 bacteria the fatty acids occurring as glycerides are decomposed into 

 glycerin and fatty acids. The extent of fat decomposition, brought 

 about largely by molds in the opinion of some, is shown by numerous 

 -experiments with peanut cake, olive press cake, cottonseed meal, 

 almond oil, corn meal, etc. In a number of these experiments Asper- 

 gillus niger seemed to be particularly efficient in decomposing fats. 

 Analogous decornposition processes may occur in the soil as proved by 

 the experiments of Rubner. 



