GENERAL FOOD RELATIONSHIPS— METABOLISM 79 



Whether there is a special class of -phosphorus bacteria 

 remains to be discovered. That phosphorus is oxidized dur- 

 ing the activity of many bacteria is undoubted, but whether 

 this represents a source of energy or is the accidental 

 by-product of other activities is undetermined. 



Practically nothing is known about the metabolism of the 

 other elements as such. 



From the preceding brief review of the relation of certain 

 bacteria to some of the elements in the free state and from 

 the further fact that there is scarcely a known natural 

 organic compound which cannot be utilized by some kind 

 of bacterium, it is evident that this class of organisms has 

 a far wider range of adaptability than any other class, and 

 helps to explain their seemingly universal distribution. 



As to the metabolism loithin the cell, no more is known than 

 is the case with other cells, nor even as much. The materials 

 used for growth and as sources of energy are taken into the 

 cell, built up into various compounds some of which have 

 been enumerated and in part broken down again. Carbon 

 dioxide and water are formed in the latter process. What 

 other katabolic products occur it is not easy to determine. 

 Certainly some of the substances mentioned in the next 

 chapter-s are such products but it is not. always possible to 

 separate those formed inside the cell from those formed 

 outside. Perhaps most of the latter should be considered 

 true metabolic products. It would seem that on account 

 of the simplicity of structure of the bacterial cell and of the 

 compounds which they may use as food they would serve 

 as excellent objects for the study of the fundamental prob- 

 lems of cell metabolism. Their minuteness and the nearly 

 impossible task of separating them completely from the 

 medium in or on which they are grown makes the solution 

 of these problems one of great difficulty. 



When all of the environmental conditions necessary for 

 the best development of a given bacterium are fulfilled, it 

 will then develop to the limit of its capacity. This develop- 

 ment is characterized essentially by its reproduction, which 

 occurs by transverse division. The rate of this division 

 varies much with the kind even under good conditions. 



