228 ESSENTIALS OF BACTERIOLOGY 



evacuations of animals form the basis for their activity, whereby 

 nitrates, ammonias, and nitric acid result. The nitrogen 

 necessary for the growing plant is thus produced. The 

 nitromonas of Winogradsky belongs to this group. The soil 

 tends to destroy ordinary disease-bacteria in a short time, but 

 spores may remain dormant for a number of years as the 

 spores of anthrax. 



The Bacteria of Milk and Other Foods. 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 

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

 consumption usually contains thousands to millions of bacteria 

 to the cubic centimeter, sterilization or pasteurization and super- 

 vision of the dairies should always be carried out on 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 unclean 

 milk is sometimes 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 

 consumer in as short time as possible without further hand- 

 ling, keeping the container in the mean time at a low tem- 

 perature and protected from the air. Such treatment is safer 

 than any form of sterilization. 



Foods as a Source oj Injection. Foods eaten after little or 

 no cooking, such as fruits, salads, and the like, and also 

 oysters, are possible sources of bacterial diseases, and the not 

 infrequent so-called ptomain poisoning observed after the 



