PRESENT STATUS OF PASTEURIZATION OF MILK. 13 
thermal death point and, on account of the survival of a few cells, 
survive the pasteurizing process. 
The colon test as an index of the efficiency of the process of pasteur- 
ization is complicated by the ability of certain strains to survive a 
temperature of 145° F. for 30 minutes and to develop rapidly when 
the pasteurized milk is held under certain temperature conditions 
which might be 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 may, however, indicate 
improper treatment of the milk. 
_ If milk is pasteurized at a temperature of 150° F. or above for 
30 minutes, it 1s not to be expected that any colon bacilli will survive; 
consequently under such conditions the colon test for the effectiveness 
of pasteurization may be of value. It must be remembered, however, 
that a study of more cultures may reveal strains of colon bacilli that 
are able to survive this or even a higher temperature. 
MODERN THEORIES OF PASTEURIZATION. 
Pasteurization at present is looked upon with favor by medical 
- men, sanitarians, dairymen, and consumers, but the art has not been 
developed without opposition, and even now its value is not univer- 
sally accepted. Most of the objections to pasteurized milk have been 
based on theory or on experiments in which the milk was pasteurized 
at high temperatures and in view of our modern theories are of no 
great importance. 
One of the greatest objections to pasteurized milk has been that the 
heating destroyed the lactic-acid bacteria and that putrefactive organ- 
isms were left, which, when relieved from the restraining action of the 
acid-forming bacteria, would develop, forming toxins and putrefac- 
tive products (12). 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 and can not be applied to milk pasteurized at low tem- 
peratures. From the results of seven years’ work in the Dairy Divi- 
sion on commercial pasteurized milk it has been found that such milk 
sours, as raw milk does, but that the souring is delayed. Pasteuriza- 
tion for 30 minutes at temperatures of about 145° F., as is generally 
practiced in this country, does not destroy all the lactic-acid organ- 
isms, and those which survive play an important role in the souring 
of commercially pasteurized milk. 
Another objection to pasteurized milk has*been that bacteria grow 
faster in it than in raw milk. In spite of several experiments which 
