2 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE. 



•pasteurization of milk, when the process is properly performed, 

 iaffords protection from pathogenic organisms. Such disease-produc- 

 ing bacteria as Bacillus tuberculosis, B. typhi, B. diphtheric?, and the 

 dysentery bacillus, when heated at 140° F. for 20 minutes or more, are 

 destroyed, or at least lose their ability to produce disease. 



According to Mohler (l), 1 pasteurization offers protection against 

 foot-and-mouth disease. He makes the following statement : " Milk 

 which has been pasteurized for the elimination of tubercle and 

 typhoid bacilli will not prove capable of transmitting the disease 

 [foot-and-mouth] to persons or animals fed with it." In view of 

 the recent outbreak of foot-and-mouth disease in this country this 

 is of importance. 



Within recent years several epidemics of septic sore throat have 

 been traced to milk. In some of these epidemics it was found possible 

 by pasteurization to destroy streptococci which were isolated from 

 throats of infected people and which were believed to be the infective 

 agents. Pasteurization, properly performed, seems to protect against 

 epidemics of this kind, but until the organism which causes the 

 disease is definitely known it is impossible to say that it affords abso- 

 lute protection. 



Epidemics of scarlet fever have been traced to milk supplies, and 

 in such cases pasteurization has been resorted to," with apparently 

 satisfactory results, as a means of safeguarding the public health. 



Pasteurization is of value from a commercial standpoint so far as 

 it increases the keeping quality of the milk and prevents financial 

 losses by souring. As practiced at the present time, commercial 

 pasteurization, with reasonable care, destroys about 99 per cent of 

 the bacteria, and while it does not prevent the ultimate souring of 

 milk, it does delay the process. At the present time pasteurization 

 is the best process for the destruction of bacteria in milk on a com- 

 mercial scale. Many attempts have been made to destroy these bac- 

 teria by means of electricity, but its use commercially has not proved 

 satisfactory. Its action is usually indirect, the bacteria being de- 

 stroyed through the heat produced by the electric current or through 

 chemical substances produced by decomposition of the milk. It is 

 possible, however, that future research will develop some satisfactory 

 method of treating milk in this manner. 



The use of ultra-violet rays for the destruction of bacteria in milk 

 has not proved to be of value as a commercial process. Experiments 

 with these rays carried on by Ayers and Johnson (2) showed that 

 while the rays cause great destruction of bacteria in milk, when' 

 exposed under suitable conditions, the process in its present state 



1 See references to literature at end of paper. 



