CHAPTER VI 



PHYSIOLOGY OF NUTRITION AND GENERAL PRINCIPLES 



OF CULTURE 



Chemical Composition of Bacteria (27). 



The substance of bacteria, like that of all other living organisms, 

 consists for the main part of water, which constitutes about 85 per cent, of 

 their weight {human body 65-70 per cent., green plants 60-80 per cent., algae 

 about 90 per cent.). The high proportion of water (shown also in the abun- 

 dance of sap-vacuoles) is due to the fact that they are aquatic, not terrestrial 

 organisms, inhabitants of liquid media. Analysis of the substance of pure 

 cultures freed as far as possible from the culture medium has given the 

 following results : — 



These two analyses give, of course, only a general idea of the composition 

 of the bacterial cell. Other cases would probably show greater differences, 

 for bacteria are, like all other organisms, dependent in their composition 

 on the nature of the food-stuffs ■ available. Like these also they are no 

 doubt capable of selecting their food to a certain degree. 



The quantity of the ash will be larger where the surrounding medium 

 is rich in salts, and there will be a higher percentage of proteids in bacteria 

 from a nutritious peptone culture than in those nourished on glycerine and 

 ammonium chloride. Still, on the whole, their composition is evidently not 

 widely different from that of other organisms, as the above analyses show. 



