152 PRACTICAL DAIRY BACTERIOLOGY 



sibly 10 minutes. Sometimes a temperature slightly above the lat- 

 ter is adopted, but maintained for a shorter time, not more than 

 a minute. Many machines and devices invented as pasteurizers 

 produce quite different temperatures, and the effect, as would be 

 expected, is very different with different methods. This must 

 be borne in mind in trying to explain the effect of pasteurization 

 on milk, and in determining its value. 1 



The chief effects of pasteurizing are: i. The maintenance 

 of pasteurizing temperatures destroys a large part of the lactic 

 bacteria. Inasmuch as these produce no spores they are quite 

 easily killed, and as a consequence pasteurized milk will not 

 ordinarily sour. When subsequently it shows signs of spoiling, 

 as it will always do in time, the changes which appear are quite 

 different from those in normal, unpasteurized milk. 2 2. The 

 temperatures adopted are generally sufficient to kill the germs 

 of specific diseases, excepting tuberculosis. Typhoid fever, 

 scarlet fever and diphtheria germs are all destroyed by com- 

 paratively low temperatures, and pasteurization is quite sufficient 

 to kill them. Five minutes exposure to 155 will kill typhoid 

 germs, and probably also those of scarlet fever and diphtheria. 

 Whether pasteurization will destroy the tuberculosis bacillus 

 will depend entirely upon its thoroughness. These organisms 

 can be destroyed by a temperature of 160 maintained for 10 

 minutes. 3 At lower temperatures a longer application of heat 

 is necessary. At a temperature of 140 the bacillus will be 

 destroyed,* if the temperature is maintained for a couple of 

 hours under conditions which prevent the formation of a scum 

 on the surface of the "milk." 5 Hence, the efficiency of pas- 



1 Freeman. Arch. f. Pediatrics, 1896. 

 Rogers. Bui. 73, Bu. An. Intl., 1905. 



2 Severin and Budinoff. Cent. f. Bact., II., xiv., p. 463, 1902. 



3 Bang. Rev. Gen. d'Lait, I., p. 425, 1902. 



Barthel and Stenstrom. Cent. f. Bact., I., xxx., p. 429, 1901. 

 * Smith. Jour. Exper. Med., p. 217, 1899. 

 5 Hesse. Zeit. f. Hyg., xxxiv., p. 346, 1900. 



Russell and Hastings. Rev. Gen. d'Lait, III., p. 34, 1903. 



Russell and Hastings. Ann. Rep. Wis. Exper. Sta., 1904. 



