DIRTY MILK 65 



method, seven hundred thousand bacteria by' the Stewart-Slack 

 method, and five million bacteria by the direct method of micro- 

 scopic examination). . 



(c) In determining the total number of bacteria in milk, the 

 microscopic examination is far more accurate than the plate 

 method, since it gives practically all of the bacteria present, while 

 the plate method gives only those that grow in special media 

 under special conditions. The microscope, however, fails to dis- 

 tinguish between living and dead bacteria. 



(d) The Stewart-Slack method of examining milk is of great 

 practical use in those cities which have a bacterial standard of five 

 hundred thousand, since it quickly detects mUk which contains 

 bacteria more than this limit, without the necessity of making 

 a plate count. For samples that contain about five hundred 

 thousand or less, it is necessary to make a plate count in order 

 that the result may be reliable. 



(e) Insufficient data are as yet at hand to determine the factor 

 by which the milk could be condemned by the Prescott-Breed 

 method. Data at present at hand would seem to indicate that 

 nearly all samples of milk would approach or surpass this limit 

 when the bacteria are determined by the direct method of exam- 

 ination of Prescott-Breed. 



(/) No constant ratio can be found between the number of 

 bacteria disclosed by the microscope and the number found by 

 the plate count. There is a general parallel, but with many ir- 

 regularities. 



No method has yet been suggested for accurately distinguishing 

 between the pus cells and other cells that may be in the milk that 

 do not have an origin in inflammatory conditions. Some regard all 

 noticeably clumped cells as indicating pus, stating that, upon 

 proper incubation, all such dumpings may be found to be accom- 

 panied by chain-forming streptococci. Others regard all poly- 

 morpho-nuclear neutrophilic cells as pus. Most, however, at the 

 present time fail to recognize any method of clearly distinguish- 

 ing pus from tissue cells. 



A general consensus of opinion has been reached that a high 

 cell count should not alone condemn milk, although it is a matter 

 for suspicion. The cell count varies with the same cow upon dif- 

 ferent days, and it may be increased by simply manipulating the 



