CHEMICAL COMPOSITION OF BACTERIA 59 



COMPOSITION OF BACTERIA. 1 



It will be seen that from 75 to 86 per cent, of the bacterial celt is 

 water. The remainder of the cell consists chiefly of protein, carbo- 

 hydrate-like bodies, extractives (fats, fatty acids, waxes and lipoids), 

 and inorganic salts. Of these, the nitrogenous substances vary greatly 

 in amount, depending upon the composition of the medium in which 

 the organisms are grown. _ The extractives (fats, waxes, lipoids, and 

 fatty acids) are most prominent in the tubercle bacillus and the acid- 

 fast group. Some extractives, however, are found in all bacteria, 

 they being greater in amount on a medium containing carbohydrate 

 and protein than on one containing protein alone. The chemical 

 determination of the extractives is very unsatisfactory, partly because 

 of the difficulty in breaking up the cell sufficiently to facilitate the 

 entrance of the solvent. 



3. Chemical Composition of Bacteria. The percentages of the ele- 

 ments and various constituents of bacteria, as indicated in the above 

 tables, is at best only approximate. Other factors very markedly 

 influence the composition of the organisms. 



Of these, the age of the culture, the temperature at which it is 

 grown, and the composition of the medium in which the organisms 

 are grown are the most important. Generally speaking, young cul- 

 tures appear to contain rather more dry residue than older cultures, 

 and bacteria grown at 37 C. contain more dry residue than those 

 grown at 20 C. 5 The inorganic constituents of the broth influence 



1 Nicolle and Alilaire, Ann. 1'Inst. Past., 1909, xxiii, 547. 



2 Asporeless. 3 From acetone extract. < From CHCls extract. 



5 The decrease in dry residue observed in old cultures is partly attributable to auto- 

 lysis of bacteria ; this is usually observed earlier in cultures maintained at 37 C. than in 

 corresponding cultures kept at 20 C. Growth is more rapid at this higher temperature, 

 and recessive changes due partly to the accumulation of waste products are seen earlier. 



