22 



The American Public Health Association 



forms in milk produced and handled 

 under several of the most common 

 commercial conditions. Neither they 

 nor have others shown the relative 

 susceptibilities to pasteurization tem- 

 peratures of the two sub-groups. How- 

 e\'er, this information when available 

 may be of greater scientific than prac- 

 tical value, for if those of one sub- 

 group are shown to be more suscep- 

 tible to the heat than the other, the 

 practical fact would not be altered that 

 in an efficiently performed pasteuri- 

 zation operation none of either of 

 them should be found alive after the 

 minimum standard temperatures and 

 time periods of holding when the 

 standard method for determination of 

 them in 1 c. c. were used. 



It is to be strongly recommended 

 that similar quantitative tests be made 

 upon the raw milk just before pasteur- 

 ization and upon samples of the prod- 

 uct upon the completion of each of the 

 several important steps in the heating 

 and cooling processes, such as samples 

 from the first and last milks out of the 

 heater, and one or two intermediary 

 ones ; from the first and last milk from 

 the outlet of a continuous flow tank 

 or pipe holding system and several in- 

 termediary ones ; from the milk at the 

 beginning and at the end of each hold- 

 ing period from a batch pasteurizer; 

 from the first and last milks over the 

 cooler and at several intervals in be- 

 tween. 



Of special importance in this con- 

 nection have been the demonstrations 

 that substantially all market milks 

 produced under commercial conditions 

 and even the majority of certified 

 milks will show positive results in the 

 application of the standard tests for 

 the presence of members of the B. coli 

 group in 1. c. c. .innoculations. Ayers 

 and Clemmer have recently published 

 more elaborate studies on the occur- 

 rence and significance of the colon 

 count in raw milk and one of their 



conclusions is that "fresh milk pro- 

 duced under the best Conditions al- 

 ways contains some organisms of the 

 colon aerogenes group." While, there- 

 fore, it is recommended that in all 

 tests to determine the efficiencies of 

 pasteurization process by the use of 

 quantitative determinations of the B. 

 coli group, samples of the raw as well 

 as those of the fully and partially pas- 

 teurized product should be collected 

 and tested, it is evident that the results 

 of such testing of samples of the raw 

 and of the intermediary product are 

 not as necessary for final judgment as 

 are the results of the bacterial counts 

 of the same or similar samples when 

 only total counts are availa;ble. When 

 a fairly detailed history of the product 

 is available one farniliar with the sub- 

 ject can obtain much valuable infor- 

 mation and may even be able to express 

 a tentative conclusion of the first, last 

 and intermediary samples of the final 

 heated and held product even if no 

 such tests have been made of the raw- 

 milk. 



Streptococci in Relation to Pasteuri- 

 zation. With respect to the use of 

 tests for the presence of streptococci 

 in pasteurized milk, the Committee 

 knows of no published reports of 

 studies conducted under truly commer- 

 cial conditions. However, there have 

 been a number of intensive investiga- 

 tions conducted under laboratory and 

 semi-laboratory conditions. 



Davis* made extensive studies of the 

 streptococci found in various types of 

 milks, i. e., certified and pasteurized, 

 by both the flash and the holding sys- 

 tem. His work deals chiefly with the 

 haemolytic forms. His conclusion that 

 of the strains of the Streptococcus lac- 

 ticus some are haemolytic and some 

 not, although neither are virulent for 

 animals, is of importance. He found 

 the various haemolytic forms more 



*Davis, Journal of Infectious Diseases, 1916, in 

 p. 836, and 1918, 33, p. 569. 



