14 
BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE 
certain strains to survive a tempera- 
ture of 145 c F. for 30 minutes and to 
develop rapidly when the Pasteurized 
milk is held under certain tempera- 
ture conditions met during storage and 
delivery. Consequently the presence 
of a few colon bacilli in Pasteurized 
milk under ordinary market conditions 
does not necessarily indicate that the 
milk was not properly heated. The 
presence of a large number of colon 
bacilli immediately after the heating 
process indicates that the milk has not 
been heated to 145 c F. for 30 minutes 
and the test properly applied should 
be valuable in control work. Fermen- 
tation tubes can be used for making 
the test, but when gas formation is 
noted the presence of colon bacilli 
should be demonstrated by further 
tests. Often anaerobic spore formers 
are encountered which survive pas- 
teurization and give the typical fer- 
mentation tube test. 
PAST AND PKESENT THEOKIES 
OF PASTEURIZATION 
Pasteurization at present is looked 
upon with favor by medical men. sani- 
tarians, dairymen, and consumers, but 
the art has not been developed with- 
out opposition, and its value is not uni 
versally accepted. Most of the objec- 
tions to Pasteurized milk have been 
based on theory or on experiments in 
which milk was Pasteurized at high 
temperatures. In view of our modern 
theories they are of no great impor- 
tance. 
One of the greatest objections to 
Pasteurized milk has been that the 
heating destroyed the lactic-acid bac- 
teria and that putrefactive organisms 
were left, which, when relieved from 
the restraining action of the acid- 
forming bacteria, would develop, form- 
ing toxins and putrefactive products. 
It was believed that the milk, because 
it was not sour, would be consumed in 
that condition. This objection was 
based on experiments in which milk 
was heated to temperatures near the 
boiling point ancL can not be applied 
to milk Pasteurized at low tempera- 
tures. From the results of many 
years' work in the Bureau of Dairy 
Industry on commercial Pasteurized 
milk, it has been found that such milk 
sours, as raw milk does, but that the 
souring is delayed when compared 
with the souring (if the same grade of 
raw milk. Pasteurized milk sours in 
a manner similar to that of a high 
grade of raw milk, and there is no 
more reason to fear the overgrowth 
of putrefactive organisms than there 
is in any high-grade milk. Pasteuriza- 
tion for 30 minutes at temperatures of 
about 145° F.. as is generally prac- 
ticed in this country, does not destroy 
all the lactic-acid organisms, and those 
which survive play an important role 
in the souring of commercially Pas- 
teurized milk. 
Another objection to Pasteurized 
milk has been that bacteria grow faster 
in it than in raw milk. In spite of 
several experiments which seem to 
prove this point, it has never been 
thoroughly established. It has been 
found that the rate of bacterial in- 
crease is approximately the same when 
the comparison is made between raw 
milk and Pasteurized milk having 
about the same bacterial content. 
It is often stated that Pasteuriza- 
tion, even if it does destroy bacteria. 
does not destroy poisonous products 
of their growth. This can hardly be 
considered a real objection, for if they 
are present in raw milk they must be 
consumed with it, and if Pasteuriza- 
tion does not destroy them the Pas- 
teurized milk would be no worse than 
raw milk. 
The question as to whether Pasteur- 
ization destroys beneficial enzymes is 
still an open one. In the light of our 
present knowledge of the enzymes in 
milk and the part they play in the 
digestive process it is quite impossible 
to settle the question of their impor- 
tance. It is evident, however, that 
the low temperatures now in use in 
Pasteurization have little effect on the 
commonly recognized enzymes. 
The opponents of Pasteurization 
have raised an objection on the 
ground of its direct influence on the 
milk producer. It has been asserted 
that Pasteurization would cause lax 
methods of production on the farm, 
for the reason that farmers would 
know that the milk was to be Pas- 
teurized and, therefore, they could be 
careless in its production. There 
seems to be some basis for this objec- 
tion, but in any city where there is 
any inspection of the raw-milk supply 
the same inspection can and should 
be continued even though the milk is 
to be Pasteurized. 
From a chemical standpoint serious 
objections have been raised against 
Pasteurized milk, because the heating 
produces changes which render the 
milk less digestible, particularly in the 
case of infants. As has already been 
stated, however. Rupp (26) has found 
that milk Pasteurized at 145° F. for 
30 minute* does not undergo any ap- 
preciable chemical change. He found 
