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 
Gedy can generate intensely porsonons substances out 
of the body proteids. 
In the presence of oxygen the decomposition products 
that are formed by the attack of the anaérobic bacteria 
are further decomposed and oxidized by the aérobes; 
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 anaérobes—are able to live 
only in the presence of free oxygen, The facts of anaéro- 
biosis are of great importance to technical biology and 
to pathology. Since, under strictly anaérobic 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. Thns many species 
of bacteria which in albuminous media produce no 
