20 



The American Public Health Association 



the real effect of the heating process 

 by introducing the results of the action 

 of the various other factors which have 

 altered the character of the product 

 itself. It is true that the character of 

 the raw product influences greatly the 

 results of the study of the heating 

 process, but the final results alone give 

 at best only clues as to causes pro- 

 ducing them. For example, a very 

 low count milk could be passed 

 through a bacterially clean, but other- 

 wise very poorly designed or operated 

 pasteurization system and yet yield a' 

 total count, which if taken alone might 

 be acclaimed as indicative of high pas- 

 teurization efficiency. On the other 

 hand, a high count milk might have 

 been passed through a modern, well 

 designed and efficiently operated pas- 

 teurizing plant and have given the 

 same results. Still further those who 

 make use of the final total counts as 

 indicative of pasteurization efficiency 

 or the lack of it, fail to consider the 

 fact that some of the most common 

 sources of high bacterial counts in pas- 

 teurized milk have no relation what- 

 ever to the efficiency of the heating 

 processes applied or the thoroughness 

 of their application, but are essentially 

 matters of the adequacy of the previous 

 cleaning of the cooling and bottling 

 systems through which the product has 

 passed after heating. 



Interpretations of ' Results. As a 

 means of estimating the general bac- 

 terial conditions and quality of pas- 

 teurized milks, the bacterial counts as 

 standards are, as has been indicated, 

 very useful, but reliance should not be 

 placed upon them as accurate indices 

 of the efficiency of pasteurization op- 

 erations. Here again, they would be 

 of more value if there were available 

 for correlation with them, the fully 

 detailed information covered by a his- 

 tory of the milk up to the time of heat- 

 ing and of testing. 



(c) Biological Demonstrations of 

 Efficiency, Procedure C. 



C. Another procedure employed in 

 the estimation of the efficiency of pas- 

 teurization operations, calls for the de- 

 termination in the pasteurized product 

 of the presence or absence and the 

 numbers if present of bacteria of the 

 B. Coli group. Rarely also are tests 

 made for the presence or absence of 

 streptococci. Still more rarely are 

 they made for species or groups of 

 pathogenic bacteria or other micro-or- 

 ganisms and then only if cultures 6i 

 them have been added to the raw milk 

 intentionally under experimental con- 

 ditions, or if they have been found to 

 be present in the raw milk. 



It is obvious that in all of these 

 cases too, it is quite essential to have 

 available for comparison the results 

 of quantitive determinations of the 

 presence of the same types in the raw 

 milk, for otherwise any negative re- 

 sults in the tests of the pasteurized 

 product have but little significance. 



These quantitive determinations in 

 the raw and the pasteurized products 

 yield far more valuable results for pur- 

 poses of judgment of the effectiveness 

 of the heating process than the com- 

 parative total bacterial counts on the 

 same products, for the reason that 

 members of these groups are more uni- 

 form in their respective susceptibili- 

 ties to heat, and in fact to all alterations 

 of environment, than are the various 

 types of bacteria of all sorts. More- 

 over, these groups and species number 

 among their members, races and 

 strains which are themselves pos- 

 sessed, at times at least, with the 

 power of producing human disease. 

 They furnish therefore the means for 

 a closer judgment of the probable ef- 

 fects of the processes studied upon the 

 wider range of pathogenic bacteria of 

 the non-spore forming types if the lat- 

 ter had happened to be present in the 

 product under the conditions of the 



