THE RELATION OF MICROORGANISMS TO MILK. 333 



use of both the numbers and the species present in determining the 

 quality of the milk supply. 



VALUE OF BACTERIOLOGICAL MILK STANDARDS AND ANALYSES. 



Regarding the value of bacteriological standards for milk there is still 

 some difference of opinion among milk bacteriologists. The germ con- 

 tent of any lot of milk is largely dependent upon three factors: the 

 number of organisms getting into the fresh milk; the temperature at 

 which it is kept; the age of the milk when analysis is made. 



The high bacterial count in any lot of milk may be the result of any 

 one of these conditions or a combination of them. A high count means 

 that there has been carelessness either in the production, resulting in high 

 initial contamination, or in the subsequent handling permitting a rapid 

 multiplication of the organisms, or that the milk is old. 



On the other hand milk with a low germ content can be obtained only 

 where the original contamination is small and it has been held at low 

 temperatures. A low count, therefore, means care both in the production 

 and later handling of the milk. 



While the germ content may be regarded as a general index to the 

 care the milk has received, it may not at all indicate its wholesomeness. 

 A high count may be the result of the rapid growth of the lactic bacteria, 

 in which case the milk may be perfectly safe and wholesome. On the 

 other hand the count may be quite small but contain pathogenic species. 

 The bacteria count is valuable as showing the sanitary conditions of 

 production and handling, but much care should be used in the interpreta- 

 tion of such results. In some ways a direct microscopic examination of 

 the milk sediment is much more satisfactory. The skilled analyst can 

 recognize certain types which may indicate the sanitary quality of the 

 milk. With sufficient experience one can recognize streptococci, other 

 groups and leucocytes. The presence and abundance of one or more 

 of these groups may indicate the nature of the original contamination 

 and the existence of diseases in the udders of cows. If rightly interpreted 

 the information thus obtained is of much value. The weakness of this 

 method lies in the fact that it is not always possible to recognize the above 

 types of organisms. In a smear preparation it is not possible to differenti- 

 ate between pathogenic and non-pathogenic streptococci or between 

 B. coli and certain other types. The presence of unusual numbers of 



