CHAPTER V. 

 COMPOSITION OF BACTERIA. 



THE elementary composition of bacteria is the same as that 

 of the higher plants. This is also true concerning the main chem- 

 ical constituents composing their body. But the proportions of 

 these latter at times vary quite widely. Moreover, some micro- 

 organisms contain constituents not found in higher plants. 



Elementary Composition. Bacteria on analysis yield carbon, hy- 

 drogen, oxygen, nitrogen, potassium, phosphorus, sulphur, calcium, 

 magnesium, iron, aluminum and manganese. As to whether the 

 last two are essential to normal development is not certain. In 

 some species they are known to be non-essential, whereas in others, 

 for instance the Azotobacter, they seem to play an important part. 



Moisture. Moisture is essential for all plant and animal life and 

 is always abundant in actively growing cells; hence, we expect, 

 and do actually find, large quantities of water in bacteria. The 

 quantity present in the actively growing cell varies from as low as 

 70 per cent, to as high as 90 per cent. Generally speaking, young 

 cultures contain less moisture than do older cultures; this appears 

 to be true until the spore stage is reached, after which the quantity 

 of water greatly decreases. The temperature at which the cultures 

 are grown also governs in a measure the quantity of water present, 

 this being less when grown at 37 C. than when grown at 20 C. 

 The cultural media undoubtedly play "a great part in determining 

 the moisture content of the cells. It is probably rather low in 

 bacteria obtained from alkali soil or from saline waters. 



Organic Constituents. The bacterial cell contains carbohydrate- 

 like bodies, proteins, extractives (fats, fatty acids, waxes and 

 lipoids), and enzymes. In addition to these some bacteria also 

 contain pigments, toxins and possibly ptomains. The quantity 

 and quality of each, especially of the last four, vary greatly with 

 the class of organisms and the conditions under which they are 

 grown. 



Carbohydrates are really conspicuous by their absence in most 

 bacterial cells, but the following members of the carbohydrate 

 group have been recognized in varying quantities in some bacteria : 

 cellulose, hemicellulose, dextrin, starch, glycogen and a number of 

 the sugars. 



Extractives, although found to a limited extent in all microorgan- 

 isms, are found in larger quantities in the tubercle bacillus and other 



