TRANSPORTATION PROBLEMS. 



171 



The Use of Preservatives. 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 methods are illegal, and are unhesitatingly to 

 be condemned. 



The Use of Heat. A more legitimate method of obtaining the 

 same result is by the use of heat. All bacteria are destroyed by heat 

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

 organisms in milk, and thus preserve the milk from their subsequent 

 action. This has given rise to two chief methods of treating milk 

 sterilization and pasteurization. 



i. Sterilization. This means the use of heat sufficient to de- 

 troy all bacteria at once. It is perfectly possible to do this, but since 

 milk always contains spore-bearing bacteria, sterilization requires a 

 high temperature for the purpose. A temperature of boiling will 

 not destroy the spores, so it is necessary to heat the milk to several 

 degrees above boiling. This involves the use of special apparatus, 

 in which bottles of milk can be inclosed in special vessels, sub- 

 jected to steam under pressure, and subsequently hermetically 

 sealed while still within the closed vessels. Such a procedure 

 inevitably 'makes the milk rather expensive. But milk thus pre- 

 pared is supposed to be germ-free, and, consequently, should keep 

 indefinitely. Unfortunately, even these temperatures do not al- 

 ways destroy all the spores, for some samples of milk thus treated 

 have subsequently undergone fermentative changes, due to the 

 germination of the spores that are left alive. Further, it has ap- 

 peared that these later changes, due to the resisting spores, are 

 frequently such as do not change the appearance of the milk to the 

 eye, so that such milk, though containing bacteria in quantity, will 

 be drunken as pure milk. The fermentation has, moreover, filled 

 the milk with bacterial products of more or less injurious nature, 



