202 MILK HYGIENE 



sometimes be used with advantage for large herds, al- 

 though there is seldom cause, even in this case, to 

 apply it. 



In taking a herd sample, the feeding and the care of 

 the animals should not be varied in any respect, the 

 milking should be conducted by the usual persons at the 

 usual times and in the usual way ; less thorough milking 

 gives lower fat content, while particularly thorough 

 milking raises the percentage of fat. The quantity of 

 milk for the day must be mixed together and the sample 

 taken from the whole. As transitory changes occur in 

 the composition of the milk, surer results will be gained 

 from daily examinations for several days than from but 

 one examination. 



d. Determining the specific gravity of milk and whey. 

 Various instruments are used for this purpose : different 

 areometers, the pycnometer or the hydrostatic scale. 

 The areometer method is the simplest and, at the same 

 time, it is sufficiently accurate, so there is no occasion to 

 describe more in detail the other methods, which require 

 weighings. 



Quevenne's lacto densimeter, in some one of its sev- 

 eral modifications, is the areometer in common use. 

 This is made like an ordinary areometer and divided 

 into degrees which correspond to a specific gravity from 

 1.014 to 1.040, or only from 1.022 to 1.038, since, by the 

 latter division, a greater space is gained between the 

 different degrees, without unduly lengthening the in- 

 strument. From such a lactodensimeter one can easily 

 read off four decimal places. 



The milk whose specific gravity is to be determined 

 is well shaken and poured into a high glass cylinder of 

 suitable diameter; the areometer is dropped in slowly, 

 in order to prevent its bobbing up and down. [The bulb 

 should be free from adhering air bubbles.] The figures 



