BACTERIA IN MILK. 215 



should not be allowed to handle the milk ; (4) so far as pos- 

 sible the filth of the cow shed should be kept from the milk, 

 since this is probably the cause of the diarrhoeal diseases. 

 Two general rules may be given and easily followed. No milk 

 from coivs that hare auv form of udder disease should be dis- 

 tributed for drinking purposes. No person suffering from or 

 recovering from a contagious disease should be allowed to have 

 anything to do with the dairy that furnishes the public with 

 milk. 



STERILIZATION AND PASTEURIZATION OF MILK. 



The bacteria in milk are clearly the source of a large amount 

 of trouble to the dairyman. It was inevitable that the en- 

 deavor should be made to get rid of them. It is easy to add 

 to the milk various chemicals which will prevent the growth 

 of bacteria and consequently preserve the milk. Many such 

 substances have been used. There are quite a number of 

 "preservatives" on the market, which are sold to the farmer 

 to assist him in preserving his milk. The basis of most of 

 these is either boracic acid, salicylic acid or formalin. All of 

 these substances are injurious to man and their use should not 

 be allowed in preserving an article so freely used as milk. 

 Such " preservatives " are to be unhesitatingly condemned. 



A more legitimate method of obtaining the same result is 

 by the use of heat. All bacteria are destroyed by heat and it 

 is therefore possible, by this simple means, to kill the living 

 organisms in milk and thus preserve the milk from their sub- 

 sequent action. This has given rise to two chief methods of 

 treating milk, sterilization and pasteurization. 



To understand the meaning of these two processes it is nec- 

 essary to notice at the outset the ends aimed at in the treat- 

 ment. They are three in number. 



i. It is desired to reduce the number of bacteria present in 

 the milk so that it can be preserved longer without souring or 



