Classes of Manure Bacteria 319 



horse manure, Severin observed that in fresh samples 

 there "was a predominance of rod-shaped organisms, but 

 that the spherical forms began to predominate as the 

 manure grew older. A further change occurred in the 

 character and numbers of the bacteria in manure when 

 the latter was plowed into the soil. The rod-shaped 

 organisms then became proportionately fewer and the 

 spherical forms proportionately more numerous. 



It would seem, therefore, that some of the bacteria 

 prominent in the intestinal tract of domestic animals 

 are rapidly reduced in numbers in the manure pile. 

 Others hold out for a while, but are ultimately suppressed. 

 The colon bacillus is thus rapidly reduced in numbers, 

 while the members of the hay bacillus group, the so- 

 called proteus group, and of the cellulose-fermenting 

 group, increase in numbers to a greater or less extent. 



As the decomposition processes proceed and the 

 soluble organic substances disappear, the nitrous and 

 nitric ferments multiply more rapidly. Many of the 

 rod-shaped forms no longer find the conditions favor- 

 able for their growth and are gradually crowded out. 



Three stages of change, — There are, thus, three stages 

 in the bacterial characteristics of manure. During the 

 first, the intestinal bacteria are most prominent in num- 

 bers. During the second, the decay and putrefaction 

 bacteria come to the foreground. During the third stage, 

 when the organic matter is already partly mineralized, 

 the nitrous and nitric ferments become numerous and 

 lead to the accumulation of nitrates. The transition 

 periods from one state to another are gradual and their 

 length is determined by the composition of the excreta 



