SOURCES OF INFECTION- IN THE STABLE. 61 



bacteria in the milk were previously studied and found 

 to be different from the characteristic forms in the layer 

 of soil. After the straining the milk showed an entirely 

 different appearance under the microscope than before. 

 It now teemed with the same kinds of bacteria as those 

 found in the soil. In a sample taken after the straining 

 had continued for some time their number had, however, 

 greatly decreased, and soon the strained milk contained the 

 same kinds of bacteria as the unstrained milk, which 

 plainly showed that the soil particles had lost their high 

 bacterial content. By a bacteriological analysis of the 

 layer of soil this proved to be the case, as this now con- 

 tained only a very small number of bacteria. The strained 

 milk was therefore far richer in bacteria than before the 

 straining, and the keeping qualities of the milk were de- 

 creased by the straining process. We thus see that by 

 carelessness in straining germs of infection may be scat- 

 tered in the milk. The large impurities are removed 

 from the milk in the straining, but the most dangerous 

 components of these, the fermentation- starters themselves, 

 are washed into the strained milk. 



It is therefore very important to change the strainer 

 cloth often during the straining; or, if a metal strainer is 

 used, the operation should be changed occasionally by al- 

 lowing steam or hot water to pass through the strainer in 

 the opposite direction. The more unclean the milk the 

 more frequently the changing and cleaning process should 

 take place. 



In my straining experiments it was also shown that the 

 more violently the milk dropped on the strainer, the more 

 the strained milk was mixed with fine soil-particles and 

 cowbairs. The kind of strainer used also played an im- 



