THE ENVIEONMENT OP BACTERIA. 59 



per cent, of water. The organisms which grow in water, 

 like algae and fish, contain a relatively higher per cent. 

 As indicated above bacteria live only in liquids and on 

 moist surfaces. They are, therefore, essentially aquatic 

 and, as such, they hold within their cells a large amount of 

 water. 



The chemical examination of various actively growing 

 bacteria shows that they contain about 85 per cent, of 

 water. The proteins, which are necessary constituents of 

 protoplasm, make up about 10 per cent. The amount of 

 fatty substances present will vary with different species. 

 On an average they may be said to contain about one per 

 cent, of fat. Certain bacteria, like those of glanders and 

 tuberculosis, are very rich in fats, which may constitute as 

 much as 40 per cent, of the dried cells. The carbohydrate 

 group, represented by cellulose, granulose or dextrin-like 

 compounds, is at times present. The inorganic or mineral 

 constituents make up about one per cent, of the living 

 organism. 



In addition to the above components of the bacterial 

 cell other substances may at times be present. The disease- 

 producing bacteria elaborate within their cells the specific 

 poison or toxin. All bacteria, moreover, contain one or 

 more soluble ferments or enzymes. 



Carbon. — The contents of the living cell are made out 

 of the food on which the organism lives. The majority of 

 bacteria differ from the higher plants in one marked 

 respect, and that is, that they do not contain chlorophyll. 

 It is by the aid of chlorophyll, in the presence of sun-light, 

 that the higher plant assimilates the carbonic acid of the 

 air. The carbon is retained by the plant while the oxygen 

 is, as it were, exhaled and returned to the atmosphere. 

 Consequently, the source of the carbon, present in the 

 higher plant as protein matter, cellulose, starch, fats, 

 etc., is the simple, inorganic compound, the carbonic acid 



