BULLETIN/ 3a2j:U,. : S. DEPARTMENT OF AGRICULTURE. 



is bo^^oi^by.-'tliEesiXite-O'f the studies of Davis (13), who found 

 that streptococci isolated from cases of sore throat were readily killed 

 by heating at 140 F. for 30 minutes. He also found that none of 24 

 strains of pathogenic hemolytic streptococci of human origin resisted 

 heating at 140 F. for 30 minutes. He makes the following statement : 



I know of no evidence that strains of streptococci pathogenic to man can resist 

 the usual temperature of pasteurization, 145 F., for 30 minutes. 



Further evidence that pathogenic streptococci are destroyed by 

 proper pasteurization was presented by the results obtained by Ayers, 

 Johnson, and Davis (7), who found that 27 strains of these organisms 

 were always destroyed by heating at 140 F. for 30 minutes. 



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 assists in preventing 

 financial losses by souring. As practiced at the present time, commer- 

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

 of the bacteria (this percentage varies, depending upon the propor- 

 tion of heat-resistant bacteria in the milk), 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 commercial scale. 



ELECTRICAL AND ULTRA-VIOLET-RAY TREATMENT OF MILK. 



Many attempts have been made to destroy bacteria in milk by 

 means of electricity, but no process has been devised which has been 

 commercially applied to any great extent. 



Alternating currents have been most extensively worked with, be- 

 cause direct currents were found to produce undesirable chemical 

 changes in milk. While the proper application of suitable alternating 

 currents has resulted in bacteria reductions similar to those produced 

 by pasteurization, it appears to be an open question as to whether 

 the action of the electric current is due to the heat generated or to 

 the direct action of electricity on the bacterial cells. 



Thornton (28), who studied this question in England, came to the 

 conclusion that the destruction of bacteria must be regarded as due 

 largely to thermal changes rather than electrical, but thought his 

 results indicated some electrical action on the molecular structure of 

 the bacteria. Beattie (8, 9), also working in England on the same 

 problem, came to the conclusion that heat was not the principal fac- 

 tor in the destruction of bacteria by electricity, but found that to 

 obtain satisfactory results the temperature should not be below 145 



