62 BACTERIOLOGY. 



sufficient ease. The standard of availability is very 

 different for different bacteria. Life processes carried 

 on without oxygen do not effect any profound molecular 

 changes in the organic material which is broken up; 

 but in order that the living organism may obtain the 

 requisite quantities of energy from this mode of life, 

 a proportionately large amount of material must be 

 superficially disintegrated. Therein lies the mechan- 

 ical foundation for the power of a small amount of fer- 

 ment to cause the production of much alcohol or lactic 

 acid, and that parasites which have invaded the living 

 body can generate intensely poisonous substances out 

 of the body proteids. 



In the presence of oxygen the decomposition products 

 that are formed by the attack of the anaerobic bacteria 

 are further decomposed and oxidized by the aerobes; 

 they are thereby rendered, as a rule, inert, and conse- 

 quently harmless. Some bacteria have adapted them- 

 selves to the exclusive use of compound oxygen, using 

 those compounds from which oxygen can be obtained, 

 and others the obligatory anaerobes are able to live 

 only in the presence of free oxygen, The facts of anae'ro- 

 biosis are of great importance to technical biology and 

 to pathology. Since, under strictly anaerobic conditions, 

 any secondary oxidation of the primary decomposition 

 products is impossible, the latter accumulate without 

 formation of by-products. Many parasitic bacteria are 

 found to produce far more poison in the absence of air 

 than in its presence. 



Organized and Unorganized Ferments. All the chem- 

 ical effects of bacteria are largely dependent upon the 

 composition of the culture media. Thus many species 

 of bacteria which in albuminous media produce no 



