CHAPTER XIX. 

 PUTREFACTION, FERMENTATION, AND DECAY. 



PUTREFACTION, fermentation, and decay are in reality terms which 

 are essentially distinct although they have been greatly confused 

 and used synonymously even by professional men. As pointed out 

 by Kendall, this confusion is attributed partly to the use of terms 

 to designate certain processes which occur in nature* before these 

 changes were studied either biologically or chemically. 



Definitions. Fischer considers the term fermentation, as it should 

 be used in bacteriology, as the biochemical decomposition of nitro- 

 gen-free compounds, chiefly carbohydrates, due to the action of 

 microorganisms, and putrefaction as the biochemical decomposition 

 of nitrogenous organic compounds by the action of microorganisms. 



The distinction which is usually drawn between decay and putre- 

 factionas the decomposition of nitrogenous organic substances in 

 the presence of oxygen on the one hand, and the absence of oxygen 

 (or with a limited supply) on the other is not always sharply 

 defined. The end products in both cases may be quite similar. 

 Nencki found that in the decomposition of gelatin at 40 C. in the 

 presence of air, there were formed in four days for every 100 parts 

 of the original substance 9.48 parts of ammonia, 24.2 parts of 

 volatile fatty acids, 12.2 parts of glycocol, 19.14 parts of peptone, 

 and 6.45 parts of carbon dioxid, the other 28.53 parts being unde- 

 termined. Jeannert repeated these experiments with the exclusion 

 of air and found as the decomposition products of gelatin, carbon 

 dioxid, ammonia, a gas smelling like carbon bisulphid, acetic, butyric, 

 and valeric acids, glycocol, leucin, and a colloidin base-like substance. 

 He concluded from these and other experiments that (1) the decom- 

 position of nitrogenous substances and of carbohydrates may be 

 accomplished with access or exclusion of air; (2) in the latter case 

 the decomposition is considerably less rapid, and complete decompo- 

 sition requires a period six times as long; and (3) the more simple 

 chemical products formed are in the two cases identical. 



Nor is it a safe criterion to state that putrefaction is accompanied 

 by the formation of ill-smelling substances, for this is usually a 

 quantitative and not a qualitative difference. Moreover, Hirschler 

 has pointed out that the putrefaction of protein substances is modi- 

 fied by the presence of carbohydrates. The addition of various 

 carbohydrates, glycerin, and calcium carbonate changed the decom- 



