PASTEURIZATION 



259 



by train, taken to the milk supply depot, bottled, and again taken 

 by delivery wagons to the consumers. During each successive 

 handling and exposure to the air the milk receives more bacteria. 

 When we remember that much of the milk used in San Francisco, 

 St. Louis, Chicago, New York, and other large cities is from twelve 

 to thirty-six hours old before it reaches the consumer, and when 

 we realize that bacteria grow very rapidly in milk, we see the need 

 of finding some way to 

 protect the supply so as 

 to make it safe, par- 

 ticularly for babies and 

 young children. This is 

 done by pasteurization, a 

 method named after the 

 French bacteriologist, 

 Louis Pasteur. To pas- 

 teurize milk the best 

 method is to heat it to a 

 temperature of not over 

 140° Fahrenheit for 

 twenty minutes. By 

 such a process all harm- 

 ful germs and most of the others are killed and the milk does 

 not sour so soon. Some large milk companies pasteurize their 

 city supply by a rapid method at a much higher temperature, 

 but this slightly changes the flavor and destroys the enzymes and 

 vitamins in the milk. 



Disinfection.^ — Frequently it becomes necessary to destroy 

 bacteria with chemicals. This process is called disinfection. 

 While sunlight, dry heat, steam, and electricity kill germs, we 

 commonly apply the term disinfectant to such substances as iodine, 

 potassium permanganate, chloride of lime, carbolic acid, formalin 

 or formaldehyde, lysol, and bichloride of mercury. Of these, the 



^ Experiment to determine the most effective disinfectants. Use tubes of 

 bouillon containing different strength solutions of formaldehyde, lysol, iodine, 

 carbolic acid, and bichloride of m.ercury or other disinfectants. Expose all 

 the tubes to the air for half an hour, then plug with cotton wool. Examine 

 after one week. Results. Conclusions. 



Pasteurization of milk. 



