182 



PRACTICAL DAIRY BACTERIOLOGY 



SIGNIFICANCE OF DIRECT MICROSCOPICAL STUDY 



Other facts can be determined by microscopic study which 

 give information of value concerning the milk besides the de- 

 termination of the numbers of bacteria. It will commonly be 

 found that the specimen prepared as described in experiment 



No. 17 will show a number 

 of rather large, irregular 

 cells (Fig. 59). These rep- 

 resent cells from the cow 

 and are commonly spoken 

 of as leucocytes. If, how- 

 ever, the udder should have 

 any affection by which pus 

 is being discharged, the pus 

 will also appear in the milk 

 and appear identical with 

 the leucocytes. Does the 

 presence of leucocytes in 

 milk, therefore, indicate 



MICROSCOPE pus formation in the ud- 



That it does not nee- 



FIG. 59 SEDIMENT FROM CENTRIFUGAL- 

 IZEU MILK AS IT APPEARS UNDER THE 



The large cells are leucocytes; the smaller der ? 



ones bacteria ., , . , . . 



essanly do so is indicated 



by the fact that practically all milk shows some leucocytes. 

 They are identical with blood cells, and some of them appear 

 at all times to pass through the milk gland into the milk where 

 they cannot be distinguished from pus cells. Their presence 

 does not, therefore, mean the formation of pus. But if they are 

 especially abundant, it is believed to indicate pus formation and 

 to make the milk suspicious. 



Different observers have attempted to give some estimate as 

 to the number of these cells that may be found in pure milk so 

 as to make a standard by which it may be judged. But the 

 number given as a standard has varied with the method adopted 



