BACTERIA AND THEIR RELATION TO DAIRYING. 



quantities of nitrogen for their development, while a 

 high nitrogen content in the substratum is an absolute 

 condition of life with others. As regards the need of 

 bacteria of salts (mineral matter) they behave usually like 

 ordinary fungi. It must be especially noted that alkali 

 salts are very important for the nutrition of bacteria. 



Bacteria and Moisture. Not only the chemical com- 

 position of the substratum : but also the degree of moisture 

 in the same is, as already mentioned, of importance for 

 the development of bacteria. Organic life is inconceiva- 

 ble without a certain content of moisture in the nutritive 

 substratum. We saw above that sporeless bacteria die 

 comparatively rapidly in the absence of moisture, while 

 the spores, on the other hand, retain their power of life 

 even a long time after the substratum is completely dried 

 out. 



Bacteria and Heat. Heat, this mighty spring in the ma- 

 chinery of organic nature, is also of great importance for 

 bacteria, although the various species have very different 

 demands in this respect. It may be said in general that 

 39 F. (4 0.) is the lowest temperature at which bacteria 

 can multiply and grow. Below this temperature they fall 

 into a torpor from which they are awakened only by in- 

 creasing temperature. 



"With most bacteria the torpor-like condition appears 

 even before this temperature has been reached. Some 

 species have been found in ocean water and in the 

 soil, however, which can multiply even at 0. While 

 the development of bacteria is arrested by a low tem- 

 perature, a large number of them are able to stand intense 

 cold without being destroyed. The bacteria of splenic 

 fever are said to live even after having been subjected to 



