48 BIOLOGY AND TECHNIQUE 



cause of their action in rendering butter, milk, tallow, and allied prod- 

 ucts rancid, and are medically of interest for their action upon fats in 

 the intestinal canal. 



Enzymes of Fermentation {The Cleavage of Carbohydrates by Bacteria). 

 — The power to assimilate carbon dioxide from the atmosphere is 

 possessed only by the green plants and some of the colored algae, 

 and the sulphur or Thiobacteria. All other living beings are thus 

 dependent for their supply of carbon upon the synthetic activities 

 carried on by these plants to the same degree in which they are de- 

 pendent upon similar processes for their nitrogen supply. The return of 

 this carbon to the atmosphere is, of course, brought about to a large ex- 

 tent by the respiratory processes of the higher animals. The carbon, 

 which, together with nitrogen, forms a part of proteid combinations, is 

 freed, as we have seen in a previous section, by the processes of proteid 

 cleavage. That, however, which is inclosed in the carbohydrate mole- 

 cule, is set free by the action of yeasts, molds, or bacteria, by an enzy- 

 matic process simila.' in every respect to that described above for the 

 process of proteid cleavage. 



Fermentation. — The power of carbohydrate cleavage is possessed 

 by a large number of the yeasts and bacteria. The process, as has 

 been indicated, is of great importance in the cycle of carbon compounds 

 for the return of carbon to its simplest forms, and is, furthermore, as 

 will be seen in a later section, of great utility in the industries. In each 

 case the power to split a particular carbohydrate is a more or less specific 

 characteristic of a given species of microorganism, and for this reason 

 has been extensively used as a method for the biological differen- 

 tiation of bacteria. In the course of much careful work upon this 

 question it has been ascertained that the specific carbohydrate-splitting 

 powers of any given species are constant and unchanged through 

 many generations of artificial cultivation. Thus, differentiation of the 

 Gram-negative bacteria, the members of the pneumococcus-streptococ- 

 cus group, and the diphtheria group, can now largely be made by a study 

 of their sugar fermentations. 



In most of these cases, as far as we know, the cleavage is produced by 

 a process of hydrolysis. A convenient nomenclature which has been 

 adopted for the designation of these ferments is that which employs the 

 name of the converted carbohydrate adding the suffix " ase " to indicate 

 the enzyme. There are thus ferments known as amylase, cellulase, lac- 

 tase, etc. 



Amylase {Diastase or Amylolytic Ferment). — Amylases or starch- 



