64 THE MILK QUESTION 



course very greatly increases any error that may appear in the 

 observation, and introduces an error the extent of which cannot 

 yet be stated accurately. It may in a measure be met by making 

 the examination in duplicate and by averaging a large number 

 of plate counts. 



The chief advantages derived from the microscopic examination 

 of milk are due to the quickness of the method. 



(a) It makes possible the rapid discarding of poor samples of 

 milk, since reports upon it are possible within a very short 

 tune. 



(6) The quickness with which an examination can be made 

 makes it possible for a single laboratory to examine many more 

 samples of milk than by the older plate method, one person being 

 able to examine and report upon fifty to one hundred samples in 

 a half-day, and to make the reports upon the same day that the 

 milk is collected. 



The microscopic study of milk gives information upon the fol- 

 lowing points: 



(a) The abundance of cells which are present in the milk. 



(6) The clumping of these cells, which is frequently notice- 

 able in the centrifugal slime, but which is rarely if ever seen hi 

 milk that is examined by the direct method above mentioned. 



(c) The bacterial count. 



(d) The presence of chain-forming streptococci. (In this re- 

 port when the term "streptococci" is used, reference is made 

 to chain-forming organisms with at least six elements in a 

 chain.) 



(e) General information concerning the nature of the dirt and 

 the source of the bacteria in the milk. With a little experience, 

 one can distinguish certain types of bacteria which come from 

 farm dirt from those that come from unclean vessels. 



The estimation of the number of bacteria in milk by the micro- 

 scopic study has the following advantages and disadvantages : 



(a) It is of no value when the number of bacteria in the milk is 

 low. 



(6) The microscopic examination gives numbers of bacteria 

 vastly higher than those given by the plate method (in a series 

 of twenty comparative tests, by one member of the committee, 

 there was found an average of five thousand bacteria by the plate 



