632 APPLICATION OF METHODS OF BACTERIOLOGY 



appear in plates made after either of the above plans. The 

 special devices for their cultivation are described in the 

 chapter on Soil-organisms. 



BACTERIOLOGICAL STUDY OF MILK. 



The possibility of milk serving as a vehicle in which 

 disease-producing bacteria may be disseminated through- 

 out a community has long been recognized, and epidemics 

 of typhoid fever have been traced directly to infected milk, 

 while such diseases as diphtheria and scarlet fever are also 

 frequently regarded as being conveyed in the same manner. 



In recent years the detailed study of the milk of individ- 

 ual cows has revealed the fact that streptococcus mastitis 

 is not an uncommon occurrence in herds, and it has fre- 

 quently been observed that milk rich in streptococci may 

 prove dangerous when fed to infants and convalescents. 



Since milk is such a favorable medium for the growth of 

 a variety of bacteria it is not at all uncommon to find market 

 milk very rich in bacteria, especially if it has been collected 

 in a careless manner in dirty receptacles, in unsanitary 

 stables, and has been shipped long distances at comparatively 

 high temperatures. 



For these various reasons the bacteriological study of 

 milk has gained considerable prominence during the past 

 few years — so much so that in some localities an effort is 

 being made to establish a bacterial standard for market 

 milk — that is, milk containing more than a certain number 

 of bacteria is not regarded as suitable for use. Whether 

 such a standard can be maintained or not remains to be 

 demonstrated. The several milk commissions composed 

 of pediatrists in various large cities have established a 



