Pasteurization of Milk 



23 



often in certified milk than in the pas- 

 teurized. Some of them were of the 

 human variety as indicated by various 

 tests applied. 



Avery and Cullen** have divided the 

 haemolytic streptococci into two 

 groups by means of their final hydro- 

 gen ion concentrations. Their haemo- 

 lytic group includes both those of 

 human and of bovine origins. They 

 showed that substantially all of those 

 of human origin reached final concen- 

 trations of pH. of from 4.8 to 5.3, 

 whereas those of bovine types with 

 but few exceptions and those of more 

 or less doubtful bovine origin reached 

 Ph. of from 4.3 to 4.5. They propose a 

 method of rapid differentiation of these 

 two types. 



The most applicable researches to 

 the problem before us are those of 

 Ayers, Johnson and Davis.* They in- 

 vestigated a wide range of organisms 

 collected from many sources. By va- 

 rious tests both by cultural and animal 

 inoculation measures they divide them 

 into two groups. Those of Group A 

 were all haemolytic many of them 

 pathogenic and all had thermal death 

 points of 140 degrees F., (60 degrees 

 C), or lower — chiefly lower. The other 

 Group B., contained a very few con- 

 cerning the pathogenicity of which 

 there was some question, but they 

 were chiefly non-pathogenic and were 

 generally non-haemolytic, and the ma- 

 jority had high thermal death points. 



They likewise correlated the two 

 groups thus separated with a division 

 through the application of the results 

 of hydrogen ion determinations. Thus 

 the A. series gave Ph. figures of from 

 5.4-6, while the B. series showed from 

 4.5-4.7. They believe that pathogenic 

 streptococci (Group A. type) are de- 

 stroyed by the proper pasteurization 

 of milk at 140 degrees F. (60 degrees 

 C.) for thirty (30) minutes. They feel 



**Avery and CuUen, Journal of Experimental 

 Medicine, Vol. XXIX, No, 2. February 1, 1919, p. 

 215. 



*Ayers, Johnson and Davis, Journal of Infectious 

 Diseases, 1918, 23,« p. 290. 



it desirable to have their work con- 

 firmed before coming to any definite 

 conclusions. 



The Committee feels that while 

 enough has been done to indicate 

 clearly that a proper application of 

 heat to a temperature of 140 degrees 

 F. for a minimum period of thirty min- 

 utes will destroy substantially all the 

 pathogenic streptococci in milk still 

 they believe as already expressed that 

 a margin of safety for biological rea- 

 sons calls for the use of higher tem- 

 peratures of not lower than 145 degrees 

 F The Committee does not feel that 

 there has as yet been suggested any 

 easy and reliable bacteriological method 

 for the determination of pasteuriza- 

 tion efficiencies by tests for strepto- 

 cocci in the final product or by a com- 

 parison between the findings as to 

 these forms in the raw and pasteurized 

 samples. 



As to studies upon other groups of. 

 bacteria having pathogenic powers, 

 there is but little requiring comment. 

 In so far as bacteria of known patho- 

 genic properties is concerned, the op- 

 portunities for their use in determina- 

 tions of the efficiencies of commejr- 

 cially operating pasteurization proc- 

 esses will be very infrequent. Of ne- 

 cessity these bacterial forms must 

 have gained access to the milk acci- 

 dentally and have been found present 

 in the raw product and their approxi- 

 mate numbers there determined, be- 

 fore any failure to find them in the 

 pasteurized samples would have sig- 

 nificance. The epidemiological evi- 

 dence as to the relative infectivities of 

 the same milk, raw and pasteurized, 

 would of course, be far more valuable. 



The on!)- occasions in which it 

 would be warrantable for known 

 pathogenic types to be used would be 

 in instances where the apparatus was 

 experimental in character and the 

 milks to be treated in them were never 

 to be offered for human consumption. 



