Sterilizing the Utensils 387 



filters are evidently indispensable for retaining most 

 of the bacteria present in the stable air. 



In milk drawn by hand, the germ content may be 

 materially diminished and the keeping quality increased 

 by the use of pails with small openings. In clean stables 

 and with clean cows, the improvement in the keeping 

 quality of the milk is not proportionately as marked 

 as it is in filthy stables. This, of course, is what one 

 would expect. 



It becomes important to determine how a com- 

 paratively slight initial contamination of the milk pro- 

 duced in clean dairies may be made to interfere as little 

 as possible with the keeping quality of the product. 

 There are methods now by means of which milk may be 

 freed from all, or a part, of its living bacteria. These 

 have all been tested practically or experimentally. 

 They include the subjecting of milk to centrifugal 

 force; its pasteurization or sterilization by means of 

 heat; and its partial or complete sterilization by means 

 of chemicals. 



Pressure. — Pressures of one to four tons to the square 

 inch have failed to improve materially the keeping 

 quality of milk. Pressures of ten to fifteen tons exerted 

 through a period of several days, have given much better 

 results, although the disease germs introduced into the 

 samples were not all destroyed. The effect of pressure 

 has been studied throughout a range of 200,000 pounds 

 to the square inch. It has been found that some of the 

 germs survived them all. 



Milk kept under pressure in an atmosphere of carbon 

 dioxid has been found to remain sweet for weeks, in 



