456 CONSIDERATION OF CARBON COMPOUNDS. 



ferments, or enzymes (false ferments) which are in most cases nitro- 

 genous substances closely related to the proteins. 



This classification was based on the belief that the living cell itself 

 was the acting agent. It has, however, been shown that this view is 

 incorrect and that the decomposing influence exerted by these fer- 

 ments is due to some substance produced by the living cell, from 

 which it may be separated or extracted in a more or less pure condi- 

 tion. It is consequently more in conformity with our present views 

 to apply the term enzyme to that agent which causes the decomposi- 

 tion. Enzymes are always products of the cell action of a living 

 organism, but this organism may be a micro-organism, such as the 

 yeast cell ; or it may be a highly developed plant, such as the almond 

 tree which produces emulsine, an enzyme which decomposes amyg- 

 dalin ; or it may be an animal or man, generating such enzymes 

 as ptyalin, pepsin, etc. (Enzymes will be more fully considered 

 later on.) 



The nature of the ferment generally determines the nature of the 

 decomposition which a substance suffers, or, in other words, one and 

 the same substance will under the influence of one ferment decom- 

 pose with liberation of certain products, while a second ferment 

 causes other products to be evolved. Sugar, for instance, under the 

 influence of yeast, is converted into alcohol and carbon dioxide, 

 while under the influence of certain other ferments it is converted 

 into lactic acid. 



The difference between fermentation and putrefaction is that the 

 first term is used in those cases where the decomposing substance 

 belongs to the group of carbohydrates, all of which contain the 

 elements carbon, hydrogen, and oxygen only, while substances be- 

 longing to the proteins, which contain, in addition to these three 

 elements, also nitrogen and sulphur, undergo putrefaction. The two 

 last-named elements are generally evolved as ammonia or derivatives 

 of ammonia and hydrogen sulphide, which gases give rise to an 

 offensive odor, the putrefying mass being generally designated as 

 fetid matter. 



As a general rule the oxygen of the air takes no part in either fer- 

 mentation or putrefaction, but the presence or absence of atmospheric 

 air may cause or prevent decomposition, inasmuch as the atmosphere 

 is filled with millions of bacteria, which may act as ferments when in 

 contact with organic matter under favorable conditions. 



