58 ACTIVITIES OF BACTERIA. 



3. THERMIC ACTIVITY. 



The production of warmth during the metabolism of 

 bacteria is absent from our ordinary cultures because of 

 their limited size; even luxuriantly growing, fermenting 

 fluid cultures betray no appreciable warmth to the hand. 

 On the contrary, it is undoubtedly true that the heat ex- 

 hibited by decomposing organic materials, when stored in 

 a moist condition, as tobacco, hay, manure, etc. , depends, 

 at least in part, upon bacterial activity. With the high 

 temperature which thus occurs, the conjecture of Lydia 

 Rabinowitsch, that here the thermophilic bacteria are con- 

 cerned, seems very probable. Accurate investigations into 

 the causes of these high temperatures are still lacking. 

 (Compare Rabinowitsch, Z. H. xx, 154.) 



4, CHEMICAL ACTIVITY. 



The chemical activities of bacteria, accompanied par- 

 tially by the production of light and always by a minimum 

 amount of heat, are to-day, in spite of the very numerous 

 and satisfactory investigations of the last twenty-five years, 

 only known in the roughest outlines. We often know 

 only the principal products, without being accurately in- 

 formed regarding the mechanism of their origin, the inter- 

 mediate products, or the bodies occurring in small quan- 

 tities. 



The following three principal varieties of chemical 

 activity may be distinguished: 



1. The bacteria elaborate their own body substance. 

 Regarding this the most important points have already 

 been discussed in the proper place. 



2. The bacteria secrete ferments, intended to make the 

 nutrient medium in their neighborhood more suitable for 

 assimilation. The products which thus occur in the sur- 

 roundings of bacteria may be designated as metabolic 

 products. 



3. The bacteria assimilate materials and elaborate others 

 which are true metabolic products. It is wrong in 

 principle to make a division into fermentation and 

 metabolic products, as is still sometimes attempted, be- 



