VITAL PHENOMENA OF BACTERIA. 61 
present. A complete description of these chemical 
changes is at present impossible. Chemists can as yet 
only enumerate some of the final substances evolved, 
and describe, in a few cases, the manner in which they 
were produced. Bacteria are able to construct their 
body substance out of various kinds of nutrient mate- 
rials and also to produce fermentation products or 
poisons, and they are able to do these things either 
analytically or synthetically with almost equal ease. 
This ambidextrous metabolic power exists, according 
to Hueppe, among bacteria to an extent known as yet 
among no other living things. 
In the chemical building up of their body substance 
we can distinguish, as Hueppe concisely puts it, several 
groups of phenomena: Polymerization, a sort of doub- 
ling up of a simple compound; synthesis, a union of 
different kinds of simple compounds into one or more 
complex substances; formation of anhydride, by which 
new substances arise from a compound through the loss 
of water; and reduction or loss of oxygen, which is 
brought about especially by the entrance of hydrogen 
into the molecule. The breaking down of organic 
bodies of complicated moiecular structure into simpler 
combinations takes place, on the other hand, through 
the loosening of the bonds of polymerization; through 
hydration or entrance of water into the molecule, and 
through oxidation. 
The chemical effects which take place from the action 
of bacteria are greatly influenced by the presence or 
absence of free oxygen. The access of pure atmos- 
pheric oxygen makes the life processes of most bacteria 
more easy, but is not indispensable when available 
substances are present which can be broken up with 
