4 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE. 
is borne out by the results of 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 
changesin 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° 
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