152 AGRICULTURAL BACTERIOLOGY 



bacteria that are introduced into the milk, as these organ- 

 isms do not pass from the intestine through the blood and 

 appear in the milk directly. They may, however, have an 

 indirect influence by changing the type of the bacterial 

 flora in the manure, some of which nearly always finds its 

 way into the milk from the dirty flanks of the animal. If 

 the feed is such as to make the manure more liquid than 

 usual, it is more difficult to keep the animals clean. 



The use of improper feed may, however, alter the taste 

 of the milk or its value as food. Cabbage, turnips, rape, 

 wild onions, and some weeds that may be eaten in the pas- 

 ture contain certain volatile principles which are absorbed 

 directly into the circulation and. may then appear in the 

 milk, just as the odor of onions appears in the exhaled 

 breath. Where such substances are eliminated in the milk, 

 the normal taste is changed. This, of course, does not in- 

 jure the healthfulness of the milk, but it decreases its com- 

 mercial value. Certain drugs, as mercury, arsenic, or 

 strychnine, if given to cows, may be eliminated with the 

 milk. The milk of an animal receiving medicine should 

 not be used for human food, and especially for the feeding 

 of children. Fats readily absorb any odors with which 

 they come in contact, and milk, by reason of its cream 

 content, thus absorbs some odors, such as that of bananas, 

 with especial avidity. In order not to injure the flavor 

 of the milk, it should be kept and handled in an atmos- 

 phere that is free from odors of all kinds. These absorbed 

 odors are often difficult to differentiate from those due to 

 the growth of bacteria in the milk. 



Contamination of other foods than milk. There are few 

 foods that are handled in such a condition as to make them 

 comparable to milk. Most of them are protected from the 

 invasion of microorganisms. Others, while subject to con- 

 tamination, do not permit the growth of the organisms that 



