708 VETEEINAEY HYGIENE 



course, quite distinct from ordinary milk both in colour 

 and composition. 



The milk should be inspected in a tall glass measure, by 

 which its colour can best be observed, while any deposit 

 can be secured for microscopical examination. 



The reaction of normal milk is alkaline, but some speci- 

 mens may give both an acid and alkaline reaction, due to 

 the presence of acid phosphates and carbonates of the 

 alkalies. By warming the milk the alkaline reaction is 

 rendered more pronounced, but it has no effect on the acid 

 reaction. 



The specific gravity varies from 1030 to 1033, but this 

 presupposes that the temperature at which the examina- 

 tion is made is 60° F. Eoughly speaking, a rise of ten 

 degrees above 60° F. corresponds to a fall of one degree 

 in the specific gravity. A correction has therefore to be 

 made for temperature, unless the milk is warmed or cooled 

 to the required degree. A lactometer is generally employed 

 to ascertain the specific gravity, but greater accuracy can 

 be obtained by the use of the specific gravity bottle. 



The specific gravity may be higher or lower than that 

 given above, which are the means of a large number of 

 observations of mixed milk : that from single cows is more 

 liable to variation, and may be as low as 1026 or as high 

 as 1038. 



The specific gravity is often used as a test of adulteration ; 

 fat has a lower specific gravity than water, and the solids 

 not fat have a higher. A high specific gravity may mean 

 the milk has had its fat removed. A low specific gravity 

 might mean either that water had been added to the milk, 

 or on the other hand, that it was unusually rich in fat. 

 No definite statement can be based on the specific gravity 

 alone. 



The total sohds can only be obtained by evaporating a 

 definite amount of milk, and drying it for some hours at 

 212° F. until the weight becomes constant. 



The fat in milk exists as an emulsion, and on standing 

 rises to the surface as cream, of which there may be from 



Digitized by Microsoft® 



