TRANSFORMATIONS OF CARBON AND NITROGEN. 8 1 



Of the many species of bacteria associated with putrefaction 

 some are likely to be found under one set of conditions and 

 others under different conditions. Some are particularly com- 

 mon in decaying vegetable substances (Fig. 1 2) and others in 

 decaying animal tissues (Fig. 1 3), while some are most char- 

 acteristic in fermenting urea. No sys- 

 tematic attempt has been made by bac- 

 teriologists to classify this miscellaneous 

 host of putrefactive organisms, nor do 

 we know as yet to what extent the dif- 

 ferent kinds of putrefaction may be pro- 

 duced by the same species of bacterium Proteiis vulgar ts found in 



. caying animal tissue. 



under different conditions. We know 



that they include cocci, bacilli and spirilli. We know that 

 some of them produce their fermentation only when oxygen 

 is present, while others do so in the absence of oxygen, and 

 we know further that the by-products produced in the ab- 

 sence of oxygen are different from those produced in its 

 presence, since the former are more likely to be of a poisonous 

 nature. We know that these decomposition bacteria occur 

 practically everywhere in nature. They are in the air, in all 

 bodies of water and are present in extreme abundance in the 

 soil. They are so widely distributed and so abundant that 

 they are sure to be on hand to seize hold of any bit of nitrog- 

 enous organic matter, which, having become lifeless, can 

 serve them as food. Every bit of excreted urea, even that 

 secreted by the smallest insects, every dead animal body 

 whether small or great, eveiy bit of vegetable matter whether 

 it be leaf, branch or fruit, provided it contain proper moisture, 

 is sure to be appropriated as food by some of these ubiquitous 

 putrefactive bacteria. The material is used as food by the 

 bacteria, and, as a consequence, they multiply rapidly within 

 the decaying substances, developing vigorously for a time, 

 until they have used up the food ; then their growth is checked 

 7 



