2 3 o MILK AND THE PUBLIC HEALTH CHAP. 



bacteria per unit of volume is really only possible with an 

 exactly denned procedure, and is meaningless when applied as a 

 statement referable to milk generally and without regard to 

 a rigidly denned laboratory procedure. It may be urged that 

 these objections can all be answered by the provision of a 

 uniformly accepted, easily performed, and exactly defined 

 laboratory procedure. While this would greatly increase the 

 practical utility of bacterial milk counts it is not possible to 

 eliminate all variants and to obtain absolute uniformity of 

 procedure. Chemicals vary, the reactions of media alter 

 with time, etc. These and other slight variants prevent any 

 absolute uniformity. 



(&) A second objection to this measure of pollution is that 

 it makes no distinction between bacterial pollution before and 

 that after the milk leaves the cow. It has been shown that 

 milk, as delivered from the teats, frequently contains large 

 numbers of staphylococci, and, to a lesser extent, streptococci 

 and other organisms. We have no evidence that such organ- 

 isms are harmful, or any reasonable grounds for demanding 

 that milk containing them should be rejected. Every pre- 

 caution in regard to milking may be taken to prevent external 

 contamination, but they will still gain access and be counted 

 as so many bacteria in the milk. The measurement is not 

 purely one of external contamination. It is not the presence 

 of large numbers of bacteria as such which is bad, but numer- 

 ous bacteria are objected to because their presence shows that 

 the methods of obtaining and handling milk used are such as 

 permit undesirable bacteria-laden matter to gain access, matter 

 which may contain harmful organisms. 



(c) A third objection only applies to vended milk. While 

 the general bacterial estimation, in spite of the above draw- 

 backs, is capable, under rigidly defined conditions, of being 

 used as a fairly accurate measure of the amount of pollution 

 in samples collected at the farm, it cannot under present con- 

 ditions serve to gauge the outside pollution of samples of milk 

 collected as vended. An ordinary sample of vended milk 

 obtained under reasonably clean conditions, and with but little 

 outside bacterial pollution, may show, owing to multiplica- 

 tion of the bacteria, a much higher bacterial count than an- 

 other sample collected under conditions of gross neglect, but 



