METHODS OF REDUCING THE GERM CONTENT 535 



survived at 60° C, 94.44 per cent, at 62.9° C, and 50 per cent. 

 at 68.3° C. At 73.9° C. all streptococci from milk and cream were 

 destroyed. Long-chained streptococci, which are considered by- 

 some authors to be pathogenic, were less resistant to heat than 

 short-chained ones. These tests were made under laboratory 

 conditions similar to commercial pasteurization and have, there- 

 fore, practical significance. 



It is interesting and important to note that Ayers and John- 

 son, in an experimental study of the thermal death-points of 

 pathogenic streptococci, found that none survived heating in 

 milk to 60° C. (140° F.) for thirty minutes. 



In another connection it has been mentioned that some strains 

 of Bacillus coli are able to survive pasteurization at 62.8° C. 

 (145° F.). Since lactic acid bacteria of both the B. coli and strep- 

 tococcus group survive, pasteurized milk will sour much as does 

 raw milk. The chief difference lies in the fact that in pasteurized 

 milk streptococci are more likely to gain ascendency over the Ba- 

 cillus coli group than in raw milk. Therefore sour pasteurized milk 

 will show the effect of Streptococcus lacticus more plainly than 

 raw milk. That is to say, the curd will be uniform, there will be 

 very httle gas, and the taste will be that of lactic acid. The 

 souring process will be delayed, of course, on account of the de- 

 struction of many lactic acid bacteria. The so-called beneficent 

 bacteria exist in pasteurized milk, and "nature's danger signal" 

 is in operation in pasteurized as weU as in raw milk. Peptonizing 

 bacteria survive, too, but the proportion of these is smaller than 

 in raw milk, so that the digestion of milk proteins rarely occurs. 

 There is less danger from peptonizing bacteria in pasteurized milk 

 than in raw milk, and a valid objection to pasteurization on this 

 score is not tenable. 



A common objection to pasteurization is the alleged alteration 

 that heat produces in milk. Appearance, taste, odor, and di- 

 gestibihty are said to be affected. It is true that boiling does 

 change the appearance, and that a cooked taste and odor are 

 acquired. In milk pasteurized at 145° C. for thirty minutes these 

 alterations, if there are any, are so slight as to be unnoticeable. 

 This subject has been discussed in detail on page 131. As to di- 

 gestibihty, it has been said that pasteurized milk is the cause of 

 scurvy and rickets. Milk is more commonly boiled in Holland, 

 France, and Germany than in this country, and still scurvy and 

 rickets are no more frequent in these countries "than here in the 

 United States. In reahty, these disorders are scarce everywhere 

 and yield readily to simple treatment. Freeman has analyzed 

 356 cases of scurvy investigated by the T^erican Pediatric 

 Society, with the following results: 60 per cent, were due to 



