DIRTY MILK 83 



kind of bacteria, moulds, or yeasts which happen to be 

 present and take part in the process. 



Milk either putrefies or ferments. Putrefaction and 

 fermentation are two general terms which include a great 

 variety of changes which take place when milk or any 

 other organic substance undergoes decomposition. By 

 putrefaction we understand more particularly the break- 

 ing-down of nitrogenous substances, while fermentation 

 deals more particularly with the breaking-down of the 

 sugars and starches. The two processes are not only ex- 

 ceedingly unlike, but have a very different health signi- 

 ficance. Putrefaction and fermentation do not, as a rule, 

 take place in the same substance at the same time. In a 

 mixture containing both albuminous substances and car- 

 bohydrate substances, fermentation takes precedence; that 

 is, the carbohydrates will ferment before the albumins pu- 

 trefy. In this sense the carbohydrates protect the proteins. 

 Hence milk, which contains both albumins and carbohy- 

 drates, almost always ferments and rarely putrefies. 



Some of the products of putrefaction are poisonous. 

 They are popularly called ptomaines. As a matter of fact, 

 ptomaines themselves are not really very poisonous, but 

 toxic substances whose composition is not clearly under- 

 stood are beUeved sometimes to be produced during the 

 putrefactive process. It is interesting to note that it is 

 almost always the intermediate products of putrefaction 

 that are dangerous, while the end products of putrefaction, 

 such as carbon dioxide, nitrates, etc., have no sanitary sig- 

 nificance in this connection. On the other hand, it is the 

 end products of fermentation, such as acids and alcohol, 

 which are poisonous in suflBcient concentration whereas the 

 intermediate products of fermentation have httle or no 

 poisonous action. i ' 



Putrid milk need not be decidedly foul. In fact, the early 

 stages of putrefaction, when the milk is only bitter due to 

 the formation of peptones, may cause nausea and vomiting 



