246 ESSENTIALS OF BACTERIOLOGY 



the plants in turn utilizing the nitrogen compounds created 

 by the bacteria. 



Soil Inoculation. Artificial help to soils deficient in nitro- 

 gen-fixing organisms has been the subject of much experiment. 



Nitragin. Pure cultures of legume bacteria under the 

 above name have been tried. Dried cultures under the name 

 of nitro-bacterine have likewise been marketed, but neither 

 of these methods has proved valuable; the matter is still in 

 the experimental stage. 



CHAPTER XXXII 

 BACTERIA IN MILK AND FOOD 



The Bacteria of Milk. Milk as secreted is sterile, but 

 at every step in its passage from the cow to the consumer it 

 is liable to contamination. Even the lower portion of the 

 teat is a source of infection, owing to the presence of stag- 

 nated milk from the former milking, and, as milk ready for 

 consumption usually contains thousands to millions of bac- 

 teria to the cubic centimeter, sterilization or pasteurization 

 and supervision of the dairies should always be enforced for 

 milk used for infant feeding. 



A standard milk should be free from pus and should not 

 contain more than 10,000 bacteria to the cubic centimeter. 



Leukocytes are normally found in milk, and only when 

 their number exceeds one million and pyogenic organisms are 

 also present can pus be said to exist. Pasteurization of un- 

 clean milk sometimes renders it more dangerous as a food 

 than untreated milk, because, by preventing the action of 

 lactic-acid formers, other bacteria are permitted to develop 

 and produce pathogenic toxins. 



Pure Milk. A pure milk is one that is obtained from a 

 healthy cow, well groomed, in a clean room, by a healthy, 

 clean person, in clean cans or bottles, and transported to the 



