122 BACTERIOLOGICAL METHODS 



bining the use of an eye-piece micrometer scale with that of the 

 hemacytometer, and it is suggested that such a combination be 

 used, not only for milk examination, but also for making many of 

 the cytometric counts of food products. 



A practical method for determining the fat content of milk by 

 means of the compound microscope was worked out in the bacterio- 

 logical laboratory of the California College of Pharmacy. The pro- 

 cedure is as follows: Make dilutions of the milk from 1-150 to 

 1-200, using distilled water or normal salt solution (0.6 per cent.) 

 and count the fat globules by means of the hemacytometer or the 

 special counter above suggested. Numerous counts made have 

 shown that 578,100,000 fat globules in i cc. of milk corresponds to 

 i per cent, of butter fat. This number was obtained by comparing 

 the fat globule count with the fat determination by the standard 

 chemical method (combined with the use of the centrifugal 

 machine). The following are a few comparisons as they were ob- 

 tained in the laboratories of the California College of Pharmacy. 



1,383,000,000 fat globules per cc. corresponded to 2.30 per cent, of butter fat. 

 933,000,000 fat globules per cc. corresponded to i . 60 per cent, of butter fat. 

 566,000,000 fat globules per cc. corresponded to i . 10 per cent, of butter fat. 

 470,000,000 fat globules per cc. corresponded to 0.80 per cent, of butter fat. 



Dividing the sum total of the several counts of fat globules 

 made by the sum total of the corresponding percentages of butter 

 fat, gives 578,100,000 the average number of globules in i cc. of 

 milk corresponding to i per cent, of butter fat. From this it will 

 be seen that in round numbers, 2,000,000,000 fat globules per cc. 

 represent a fair quality of milk, that is, milk having somewhat over 

 3.50 per cent, of butter fat. According to comparative tests made, 

 the microscopical method is fully as accurate and reliable as the 

 chemical methods. The microscopical method is not recom- 

 mended for routine procedure in dairying establishments but it 

 is certainly a most valuable adjunct to the food laboratory 

 methods. It could at all times be employed as a substitute for 

 the chemical fat determination if for any reason the latter method 



