MUNICIPAL HYGIENE 709 



8 to 10 per cent, by bulk in ordinary milk, or very much 

 higher, as in the case of certain breeds of cattle. One part 

 of cream corresponds roughly to 0'2 of fat. 



To ascertain the amount of fat in milk, a definite quantity 

 of the fluid after well mixing so as to distribute the oil 

 globules, is dried as above, and the fat extracted by ether 

 in a special apparatus. It is then weighed after thorough 

 drying. 



The dried milk from which the fat has been extracted 

 may be carefully incinerated, and the amount of ash thus 

 obtained weighed. 



The fat may be ascertained by Babeock's method which 

 is very simple. A known bulk of milk is introduced into a 

 special tube with a narrow graduated neck ; sulphuric acid 

 is added and the mixture centrifugalized, which causes 

 the fat to collect in the neck where the amount can be read 

 off. 



The above simple analysis gives the total solids in the 

 milk, the fat, ash, and the solids not fat. Beyond that it is 

 hardly necessary to go ; the determination of any alteration 

 in the proteids of milk might be desirable information in 

 udder disease, but would be a much more complex proceed- 

 ing than the above ; alterations, on the other hand, in the 

 proportion of sugar are readily determined by Fehling's 

 Solution. 



Sources of Contamination. 



The microscopical examination of milk should normally 

 only reveal the milk globules, but epithelium, hair, and 

 fragments of vegetable fibre are met with in milk which is 

 not pathogenic. The epithelium is derived from the teats, 

 the hair from the udder, and the vegetable fibre from 

 anything which has dropped off the udder into the pail, 

 ranging from fragments of food to portions of faeces. In 

 pathogenic cases blood and pus cells and casts of the milk- 

 ducts may be seen microscopically. 



Whether the milk be normal or pathogenic, innumerable 

 organisms may be seen by allowing it to stand sufficiently 



Digitized by Microsoft® 



