CHEMICAL COMPOSITION 71 



pabulum increases the protein, a plentiful supply of carbo- 

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

 and vice 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: carbon, 

 vJiydrogen, oxjjgen, nitrogen, sulphur, phogphoTus, chlorine, 

 potaBsfum, calcium, magnesium, iron, 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 water. 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 asA has been shown by different 

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

 30 per cent, of the dry weight. 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. 



It has already been stated that the essential structures in 

 the bacterial cell are cell wall and protoplasm, including 



