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 molecular structure into simpler 

 combinations takes place, on the other hand, through 

 the loosening of the bonds of polymerization; through 

 hyd ration 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 



