RELATION OF BACTERIA TO DAIRY PRODUCTS 567 



The advantages of the potassium iodide starch test are the 

 cheapness and ease with which the reagents can be procured. 

 Hydrogen peroxide is kept at every drug store and should cost 

 not more than 50 cents a pound. Potassium iodide is a com- 

 mon drug. The solutions can be procured from the druggist 

 or can be made at home. They keep well and will not need 

 to be renewed at very frequent intervals. 



The test can be applied to sweet or sour milk, buttermilk, 

 or whey. In the case of the latter, the color is not exactly like 

 that in milk, but is more of a greenish brown. It must be re- 

 membered that it is not the particular color that is to be noted, 

 but the development of any color whatever. 



The critical point for these tests is 176° F. Milk or other 

 products subjected to this temperature, or higher temperatures, 

 will not respond to the test. If the milk has been heated from 

 160° F. to 173-4° F., the color develops slightly more slowly 

 than in raw milk, becoming more slow in appearance as the 

 temperature approaches the critical point. In mixtures of raw 

 and heated milk, the same effect is noted. 



Some types of pasteurizing apparatus may fail to heat all 

 parts of the milk to the temperature indicated by the ther- 

 mometer. If any considerable portion of the milk is not being 

 heated sufficiently high, the use of the test should reveal the 

 same. Thus the operator will not be led into a false sense of 

 security by relying wholly on the thermometer. 



Infectious mastitis 



Not infrequently dairymen have serious trouble with in- 

 flammation of the udder which may be transmitted from one 

 cow to another. In stables where milking machines are used, 

 this trouble sometimes becomes very serious. This form of 

 udder inflammation is caused by certain types of bacteria 

 which probably gain entrance through the end of the teat. 



