20 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE. 
THE COLON TEST FOR EFFICIENCY OF PASTEURIZATION. 
In a study (6) of the ability of colon bacilli to survive pasteuriza- 
tion it was found that certain strains could survive pasteurization at 
145° F. for 30 minutes. On examining 174 cultures of colon bacilli it 
was found that at 140° F., the lowest pasteurizing temperature, 95 
cultures survived; at 145° F., the usual temperature for pasteuriza- 
tion, 12 survived. In each case the heating period was 30 minutes. 
Considerable variation was observed in the thermal death point of 
the colon bacilli which survived at 145° F. When the cultures which 
withstood the first heating were again heated it was found that many 
did not survive, and in each subsequent heating different results 
were obtained. Colon bacilli have a low majority thermal death 
point but on account of the resistance of a few cells, they may survive 
the pasteurizing process. 
The colon test as an index of the efficiency of the process of 
pasteurization 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 tempera- 
ture conditions met during storage and delivery. Consequently 
the presence of a few colon bacilli in pasteurized milk under ordi- 
nary 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° F. for 30 minutes and the test properly 
applied should be valuable in control work. Fermentation 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 fermentation tube test. 
PAST AND PRESENT 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 its value is not universally ac- 
cepted. Most of the objections to pasteurized milk have been based 
on theory or on experiments in which the milk was pasteurized at 
high temperatures. In view of our modern theories they are of no 
ereat importance. j 
One of the greatest objections to pasteurized milk has been that 
the heating destroyed the lactic-acid bacteria and that putrefactive 
organisms were left, which, when relieved from the restraining action 
of the acid-forming bacteria, would develop, forming toxins and 
putrefactive products. It was believed that the milk, because it 
was not sour, would be consumed in that condition. This objection 
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