62 CHEMICAL ENVIRONMENT 



kind and amount of food material available— a rich protein 

 pabulum increases the protein, a plentiful supply of carbo- 

 hydrates or of fat results in the storing of more fat especially, 

 and m'cc versa. These facts must be borne in mind in con- 

 sidering the chemistry of bacteria. 



Of the chemical elements known, only the following 

 seem to be essential in the structure of bacteria: (1) Carbon; 

 (2) hydrogen; (3) oxygen; (4) nitrogen; (5) sulphur; (0) 

 yhosphorus; (7) chlorine; (8) potassium; (9) calcium; (10) 

 magiiesiinn; (11) iron; (12) manganese. Other elements, 

 as sodium, iodine, silicon, aluminum, lithium, copper, etc., 

 have been reported by different analysts, but none of them 

 can be regarded as essential, except possibly in isolated 

 instances. 



These elements exist in the bacterial cell in a great variety 

 of combinations, of which the most abundant is ivater. The 

 amount of water varies in different species from 75 to 90 

 per cent of the total weight in growing cells, and is less in 

 spores. The amount of ash has been shown by different 

 observers to vary from less than 2 per cent to as much as 

 30 per cent of the dry iveight. The following table com- 

 piled from various sources will give an idea of the relative 

 abundance of the different elements in the ash: 



As to the form in which the last six elements in the table 

 exist in the cell, little is known. The sulphur and phos- 

 phorus are essential constituents of various proteins. The 

 high percentage of phosphorus points to nuclein compounds 

 as its probable source. 



The carbon and nitrogen, together with most of the 

 hydrogen and oxygen not united as water, make up the 

 great variety of organic compounds which compose the 

 main substances in the bacterial cell. 



