50 BIOLOGY AND TECHNIQUE 



cleavages is not entirely clear. It is believed, however, that most of 

 the cleavages are of an hydrolytic nature. 



In general, the action of the protein-splitting ferments is com- 

 parable to that of the pancreatic ferment trypsin, and they arc most 

 often active in an alkaline environment. They differ, among them- 

 selves, in the extent to which they are able to reduce the protein 

 molecule to its simple radicles, some types leading to a relatively 

 mild cleavage, while others, of the proteus type, yield ammo acids. 

 Many species of bacteria which are unable to secrete a proteolytic 

 enzyme, nevertheless produce erepsin-like ferments which readily 

 attack peptones or polypeptides, with the formation of amino acids. 



A distinction is occasionally made between the terms putrefaction 

 and decay, the former being used to refer to the decomposition 

 taking place under anaerobic conditions, that is, in the absence of 

 oxygen, a process resulting in the production of amino acids, H 2 S, 

 indole, skatole and particularly the mercaptans, which cause the 

 highly offensive odor characteristic of this type of decomposition. 

 The gases generated in such decomposition are largely made up of 

 C0 2 and hydrogen. The coincident presence, furthermore, of the 

 carbohydrate-splitting bacteria and of denitrifying microorganisms 

 renders the actual process of putrefaction a chaos of many activities 

 in which the end-products and by-products are qualitatively 

 determinable only with little precision, and which completely 

 defies any attempt at quantitative analysis. Decay is the term used 

 to signify decomposition under aerobic conditions, leading primarily 

 to the formation of amino acids, which are as a rule, changed further 

 to carbon dioxide, water and ammonia, often together with H 2 S and 

 less completely decomposed substances, such as indole and various 

 amines. Mercaptans are never formed and the foul odor of putre- 

 faction is not present in this aerobic proteolysis. 4 



Ptomaines. Very early in the study of the products of bacterial 

 growth, a number of well defined crystalline basic substances were 

 isolated from protein material which had undergone bacterial putre- 

 faction. These received, as a class, the name of ptomaines (from 

 TTTto/Aa, a dead body), and were shown to be toxic when fed to 

 or injected into animals. It was attempted, at the time of their 

 discovery, to explain the action of pathogenic bacteria on the basis 

 of a production of ptomaines or related substances. This soon 



4 Eettger and Newell, Jour, of Biol. Chem., xii, 1912, 341. 



