PLATE 4. (a) BACTERIA PLATES 



High- and low-bacteria milks. The spots are bacterial colonies each of which 

 has developed, in the jelly-like medium, from a bacterium or group of 

 bacteria in a minute amount of the milk. Bacteria "counts" indicate the 

 numbers of colonies developing from precisely measured quantities of 

 milk, reduced to a basis of "bacteria per cubic centimeter." (Courtesy of 

 the New York Milk Committee and Dr. Chas. E. North.) 



(6) DIRT TESTS 



Dirt strained out of four kinds of milk by use of small cotton disks. The 

 dirt is mostly manure and contains great numbers of bacteria. Such 

 manure may contain the germs of bovine tuberculosis. This is a ready 

 practical method of demonstrating the results of dirty or careless milking, 

 though it cannot take the place of the far more searching tests of bac- 

 teriology. (Bull. 361, U. S. Dept. of Agriculture.) 



