BLASTS WHICB CAUSE DECAY .)( I 



disagrepable, it is preferable to pasteurize^ it, i. e., to 

 place the bottle of milk in water which is heated to 155° 

 F. for twenty minutes, and then cooled. In practice it 

 is usually more convenient to heat the water to 155° F. 

 and then set it aside to cool slowly. Treat several 

 bottles of milk in this way (they should be stoppered 

 with cotton, or well corked) . How long does it keep 

 sweet (a bottle once opened must be discarded) ; do 

 you detect any unpleasant flavor due to the heating ? 



Pasteurizing is a legitimate process, but the use of 

 formalin and other preservatives by milkmen is to be 

 strongly condemned ; milk so treated is especially 

 harmful to infants. A rough test for formalin which is 

 sometimes used is as follows : Pour ordinary com- 

 mercial (impure) suljahuric acid slowly into a glass of 

 milk, letting it run down the side of the glass. If a 

 purple color appears at the junction of the milk and 

 acid it indicates the presence of formalin, and the 

 milk should be taken to the health officer for a test. 

 Pat a little formalin in some pure milk and make the 

 test : how great a dilution will give the test ? 



We notice that the sulphuric acid curdles the milk : 

 this is due to the fact that the milk contains a proteid 

 called casein, which (like the white of an egg) is 

 coagulated by acids (cheese is made from the casein 

 of the milk) . The curdling of milk is caused t)y an 



' See an article in the Year-Book of the U. S. Dept. of Agriculture for 1894 

 by Schweinitz; for 1895 by Moore. 



