TRAUGOTT BAUMGARTEL 15 



culture. It is clear that a particular kind of bacteria shows a different water content 

 according to whether one is dealing with a young, fully developed culture in liquid 

 culture medium or an old dying culture on solid medium. Especially rich in water are 

 the mucus-producing kinds of bacteria. Species which store lasting reserve material 

 like volutin, glycogen, or fat, and spores contain proportionately little water. 



THE DRY SUBSTANCE OF BACTERIA 



Differences in the water content of the bacterial cells lead to differences also in 

 their dry substance, in which the proportions can vary markedly between the com- 

 bustible ("organic") material and the non-combustible ("mineral") material. In gen- 

 eral, a particular kind of bacteria when cultivated on liquid medium contains more 

 water than when grown on solid medium. On the other hand, according to whether an 

 increased content of mineral salts or of carbohydrates is put into the liquid or solid 

 medium, sometimes the mineral part of the dry substance of bacterial growths is 

 greater than usual, sometimes the organic part is greater. In view of the high varia- 

 bility of the bacteria, no general statements can be made beyond this. So far as re- 

 liable researches have shown, 70-97 per cent of a bacterium's dry weight is made up of 

 organic substance, and correspondingly 30-3 per cent is mineral substance. 



THE ORGANIC DRY SUBSTANCE 



Doubtless the organic dry substance of bacteria consists of numerous compounds, 

 still in part wholly unknown, which on account of their common properties belong 

 chiefly to the proteins, carbohydrates, and fats. Like the water content of bacteria, 

 the chemical composition of the organic dry substance also varies and is different in 

 any one species according to the cultural conditions under which the colonies chosen 

 for analysis were grown. For example, it has been found that cultures of Bact. pro- 

 digiosum grown on potato contain almost 50 per cent more organic dry substance than 

 the cultures raised on yellow turnip, and that the cultures of the same species kept on 

 potato at 33° C. have more dry substance than similar cultures preserved at 16° C. 

 It is also demonstrable that four-to-six-day-old cultures on potato show a larger quan- 

 tity of organic dry substance than cultures thirteen to sixteen days old. 



Because in building their organic body substances the bacteria can adapt them- 

 selves, within definite but rather wide limits, to the nutrient medium on which they 

 are growing, there can be no generalization as to the results of chemical analysis 

 on the qualitative and quantitative composition of the organic dry substance. Ac- 

 cording to the findings in many studies, the protein content of the organic dry sub- 

 stance of most bacteria varies somewhere between 40 and 70 per cent, the carbohy- 

 drate content between 10 and 30 per cent, and the fat or lipoid between i and 10 per 

 cent. In general, therefore, proteins make up the greater part of the bacterial body; 

 then follow carbohydrates and fats or lipoidal substances. 



As is evident from precipitation and agglutination reactions, different kinds of 

 bacteria grown on the same nutrient medium and under conditions precisely similar in 

 other respects can be differentiated with respect to their proteins, so that with the aid 

 of the serological reactions they can be identified without further difficulty. Chemical 

 analysis, on the other hand, offers at present no method of distinguishing the different 



