288 APPLIED BIOLOGY 



means of electrical action. So far the nitrate fertilizers pro- 

 duced electrically are even more costly than the nitrate of 

 soda from Chile. 



(6) Bacteria in Milk. A number of kinds of bacteria 

 are useful in milk, butter, and cheese. The most common 

 bacteria in milk are those which produce lactic acid, which 

 causes milk to sour and coagulate. While this process may 

 be undesirable in milk intended for drinking, it is useful 

 in the making of certain kinds of cheese. Moreover, the 

 presence of the lactic bacteria in milk prevents the growth of 

 certain species which cause putrefaction. If milk be heated 

 to 70 or 75 C. (pasteurized), the lactic bacteria are killed 

 and others capable of producing putrefaction remain. This 

 fact leads to the belief that lactic bacteria are useful after 

 milk is taken into the stomach in that they oppose other 

 bacteria which may be harmful. There is no reason to 

 think that the lactic bacteria in milk are harmful when 

 taken into the digestive organs ; but, of course, most people 

 do not like to drink sour milk. In recent years, we have had 

 many newspaper articles on Professor Metchnikoff's pre- 

 pared milk for curing and preventing disease caused by 

 excessive development of decomposing bacteria in the in- 

 testines. Such bacteria produce poisonous substances which 

 may be absorbed by the blood and cause ill health (auto- 

 intoxication, meaning self-poisoning). The milk prepared 

 by the Metchnikoff method is believed to contain substances 

 secreted by certain bacteria whch will prevent excessive 

 multiplication of putrefying bacteria in the intestine. 

 These products of bacteria are sometimes concentrated into 

 tablets to be taken like pills or dissolved in milk before 

 drinking; but most of the tablets on the market are abso- 

 lutely valueless in physiological effect. In fact, physicians 

 are not yet agreed as to the medicinal value of such prepared 

 milk ; but one who wishes to try it should purchase the milk 

 in which the proper bacteria have been grown, for it seems 



