MILK 19 



urged against pasteurization but the "holder" process does not attain 

 this temperature. After the germicidal stage is passed, the bacteria 

 increase continuously and with great rapidity. The practical impor- 

 tance of the germicidal period is that it may be turned to account by 

 promptly finishing the necessary handling and cooling of the milk. In 

 other words, milk has a temperature of about 100F. when taken from 

 the cow, and if allowed to stand around on a hot summer day or in a 

 warm room will not cool down very much, so that the germicidal period 

 may pass and rapid bacterial multiplication may actually set in before 

 cooling and bottling the milk is begun. 



Second Stage. The second stage extends from the end of the germi- 

 cidal period to the time of curdling. Once the germicidal period is 

 passed, the lactic acid bacteria, group 1, increase rapidly both in numbers 

 and relatively to the other germs which for a while may multiply, but 

 not so fast as the lactic acid organisms. Before long, the acidity which 

 this group of bacteria produces becomes so great that other forms are 

 checked except that microbes of group 2, the coli-aerogenes group, may 

 continue to develop unless the temperature of the milk is kept below 

 64 F. If this is done the true lactic acid organisms will crowd out prac- 

 tically all other organisms and increase to many millions at curdling. 



Third Stage. The third stage extends from the time of curdling to 

 the time acidity is neutralized. When loppering takes place, the acidity 

 is so high that the lactic acid germs begin to decrease and thereafter 

 continue to fall off. Oidium lactis, certain moulds and yeasts which have 

 been in the milk from the start, grow in the highly acid medium and 

 by attacking the proteins reduce it to a neutral or alkaline condition. 



Fourth Stage. Final decomposition changes are effected by liquefy- 

 ing and peptonizing bacteria that heretofore have been inactive. They 

 find the alkaline condition favorable for growth and assail the casein 

 with avidity, accomplishing the ultimate decompositional changes. 



Bacterial Decomposition of Milk Usually Harmless. All of this 

 must make it obvious that the development of bacteria in milk is a 

 perfectly normal process akin to others that take place wherever organic 

 matter is undergoing decomposition. It is evident, too, that the process 

 is not ordinarily fraught with danger to man. The harmless lactic acid 

 bacteria usually carry the disintegration to the point where milk becomes 

 inedible. It is relatively exceptional for putrefying or peptonizing 

 organisms to play the master part in milk decomposition and the germs 

 of communicable disease gain access to milk comparatively infrequently. 

 Still, experience teaches that there is a real danger in impure milk, and 

 in the United States and elsewhere it is customary to spend large sums of 

 money in seeing that adequate safeguards attend the production and 

 marketing of milk. Of those milks that are looked upon as being unsafe, 

 it is usual to distinguish two sorts, namely: (1) dirty and (2) infected milk. 



