ORGANIC NITROGEN. ITS DECOMPOSITION. 51 



tion that is far from complete. It is generally produced by bacteria 

 growing in the absence of oxygen, and hence by the anaerobic or 

 facultative anaerobic bacteria. These break down the proteids, 

 but do not carry the decomposition to its final stages, the final pro- 

 duct, thus formed, being still quite complex. Many of them have 

 unpleasant odors and many of them are poisonous. 



Decay. This is the type of complete decomposition that takes 

 place in the presence of oxygen. It is produced by aerobic bacteria, 

 and results in a very complete disintegration of the decomposing 

 body. The end-products are much simpler than in the case of 

 putrefaction, and the gaseous products arising have little or no odor. 

 CO 2 ,N and H 2 O are among these final products, and are all odorless. 

 Putrefaction and decay cannot be sharply separated from each other, 

 the former being in many cases only a step toward the latter. The 

 bad-smelling or poisonous products of putrefaction will, if exposed 

 to the air, undergo further disintegration until the decay is complete. 

 But, though not sharply distinct, the difference above noted is a 

 convenient method of designating the complete decomposition, 

 in the presence of air, from the incomplete decomposition in the 

 absence of air. 



Of the many species of bacteria associated with putrefaction 

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

 and others under different conditions. Some are particularly 

 common in decaying vegetable substances and others in decaying 

 animal tissues, while some are most characteristic in fermenting 

 urea. No attempt need be made here to classify this miscellaneous 

 host of putrefactive organisms. They include cocci, bacilli, and spiral 

 forms as well as yeasts and higher fungi (Figs. 14, 15). Some 

 of them produce their fermentation only when oxygen is present, 

 while others do so in the absence of oxygen, and the by-products 

 produced in the absence of oxygen are different from those produced 

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

 nature. These decomposition bacteria occur practically everywhere 

 in nature in the air, in all bodies of water, and in extreme abund- 

 ance in the soil. They are so widely distributed and so abundant 

 that they are sure to seize hold of any bit of nitrogenous organic 



