VITAL ACTIVITIES OF BACTERIA I45 



teria are further decomposed and oxidized by the aerobes ; 

 they are thereby rendered, as a rule, inert and consequently 

 harmless. Some bacteria have adapted themselves to the ex- 

 clusive use of oxygen in combination, using those compounds 

 from which oxygen can be obtained, and others, the obliga- 

 tory aerobes, are able to live only in the presence of free 

 oxygen. The facts of anaerobiosis are of great importance 

 to technical biology and to pathology. Three types of chemi- 

 cal activity are recognized. 



1. "The bacteria develop their tissues. 



2. "The bacteria produce and liberate ferments or en- 

 zymes which tend to make the food stuff in their neighborhood 

 more assimilable. 



3. "The bacteria assimilate food and liberate it changed 

 to other material. These changes may be due to ferments re- 

 tained in the cells." 



Fermentation. Fermentation refers to the splitting up 

 or cleavage of a carbohydrate. This power is possessed by a 

 number of bacteria and yeasts. The variation in the action 

 on carbohydrates is of considerable value in differentiating- 

 species. In this connection it has been found that the specific 

 carbohydrate-splitting powers of bacteria are practically 

 constant through many generations. The cleavage process- 

 seems to be due to a process of hydrolysis. The ferments 

 causing the different fermentations have been named by 

 adding the suffix "ase" to the converted carbohydrate to in- 

 dicate the enzyme. Thus there are ferments known as amyl- 

 ase, cellulase, lactase, invertase, etc. 



Some writers refer all forms of decomposition due to 

 bacteria to fermentation, referring to the putrefactive fer- 

 mentation of albuminous substances; others limit the term to 

 the process when accompanied by the production of gas; 

 others, again, take fermentation to mean only the decomposi- 

 tion of carbo-hydrates, with or without gas-production. 



Park defines fermentation "as a chemical decomposition 

 of an organic compound, induced by the life processes of 



