STATUS OF PASTEURIZATION OF MILK 
From the results achieved from the 
proper Pasteurization of milk it seems 
evident that the thermal death point 
of pathogenic streptococci, which 
cause septic sore throat, is relatively 
low. This belief is borne out by the 
results of the studies of Davis (13), 
who found that streptococci isolated 
from cases of sore throat were read- 
ily 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 re- 
sults obtained by Ayers, Johnson, and 
Davis (7), who fount- that 27 strains 
of these organisms were always de- 
stroyed 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 re- 
sorted 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 in- 
creases the keeping quality of the milk 
and assists in preventing financial 
losses by souring. As practiced at the 
present time, commercial Pasteuriza- 
tion, with reasonable care, destroys 
about 99 per cent of the bacteria (this 
percentage varies, depending upon the 
proportion 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 pres- 
ent time Pasteurization is the best 
process for the destruction of bacteria 
in milk on a commercial scale. 
ELECTRICAL AND ULTRA-YTOLET- 
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 Lave been most 
extensively worked with, because di- 
rect currents were found to produce 
undesirable chemical changes in milk. 
While the proper application of suit- 
able 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 bac- 
terial cells. 
Thornton (28), who studied this 
question in England, came to the con- 
clusion 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 factor 
in the destruction of bacteria by elec- 
tricity, but found that to obtain satis- 
factory results the temperature should 
not be below 145° F. In the United 
States an electric process has been in- 
vestigated by Anderson and Finkelstein 
(1). Their conclusion as to the cause 
of the destruction of the bacteria is as 
follows : 
The destruction of hacteria in the 
" process is apparently due to the 
heat produced by the electric current rather 
than to the electric current itself. The 
" " process furnishes a method for 
producing a very sudden high temperature 
for a brief period of time. 
It seems evident from a review of 
the literature that in the use of elec- 
tricity, as it has been applied, suffi- 
cient heat is generated by electricity, 
or a combination of steam and elec- 
tricity, to raise the milk to the Pas- 
teurizing temperature. Since the tem- 
peratures reached are in themselves 
destructive to most nonspore-forming 
bacteria, the problem of determining 
whether the effect of electricity is 
due to heat or direct electric action 
is a difficult one. 
The use of ultra-violet rays for the 
destruction of bacteria in milk has not 
proved to be of value as a commer- 
cial process. Experiments with these 
rays carried on by Ayers and Johnston 
(5) showed that while the rays cause 
great destruction of bacteria in milk, 
when exposed under suitable condi- 
tions, the process in its present state 
of development can not replace that 
of Pasteurization on a commercial 
scale. It is difficult to obtain the 
proper exposure of milk to the rays 
on a scale sufficient to permit of prac- 
tical operation and impracticable to 
secure suitable bacteria reductions 
without seriously injuring the flavor 
of the milk. 
EXTENT OF PASTEURIZATION IN 
THE UNITED STATES 
Pasteurization when first practiced 
by milk dealers in this country was 
