CHAPTER VIII. 

 BACTERIAL METABOLISM PRODUCTS. 



BACTERIA are able to bring about enormous changes in their 

 media in a very short time. This is due in no small measure to their 

 method of metabolism which differs from that of the animal, in 

 most cases, in being a process of incomplete oxidation, whereas that 

 of the animal is a process of complete oxidation. For this reason, 

 many of the organisms of especial economic importance often leave 

 products of considerable commercial value. 



Physiologic Classification. From a physiologic viewpoint Jordan 

 divides the substances produced by bacterial metabolism into four 

 classes : 



1. The secretions, or those substances which serve some purpose- 

 ful end in the cell economy. These may either be retained within 

 the cell or may pass out into the surrounding medium. 



2. The excretions, or those substances that are ejected because 

 useless to the organism; the ashes of cell metabolism. 



3. The disintegration products, or those bodies that are produced 

 by the breaking down of food substances. Their nature is deter- 

 mined partly by the chemical structure of the nutrient and partly 

 by the specific bacteria concerned in the disintegration. Some of the 

 most conspicuous, if not the most important, of bacterial products 

 belong to this class, enzyme activity being largely responsible for 

 their existence. 



4. The true cell substance. To this class belongs the cell proto- 

 plasm, those products which are being built up into cell protoplasm, 

 and those substances which are being broken down but have not 

 yet reached the stage where they are cast off from the cell. 



The great objection which may be brought against such a classi- 

 fication is that although many products can be definitely placed, 

 others, for instance pigments, cannot. 



Carbohydrate Metabolism. Products from carbohydrate metab- 

 olism vary greatly, depending upon the species of bacteria, age, 

 medium, and whether grown in the presence or absence of oxygen. 

 Some writers distinguish six types of microorganisms, depending 

 upon the change which they produce in their media, namely: 



1. Complete oxidation which occurs only to a limited extent 

 among bacteria and then only where there is a ready supply of 

 oxygen, as is the case in a well-aerated soil in filters or on the 

 surface of decaying substances. 



2. Partial oxidation is much more common among microorganisms 

 than is complete oxidation. The product formed is also often of 

 considerable commercial value. This is the case in the oxidation 



