172 ORGANISED FLUIDS. 



The specific gravity test of the purity and richness of milk 

 is, then, one which is fallacious, and therefore but of very 

 little value. 



It has been proposed by M. Quevenne, not merely to esti- 

 mate the specific gravity of milk, but also to measure the 

 layer of cream which forms upon it by repose. This in- 

 genious method is scarcely more to be depended upon than 

 the preceding, and is put at fault by the fact that the addi- 

 tion of water favours the ascension of the cream. 



Thus, the layer of cream formed on milk to which water 

 has been added will be thicker than that of unadulterated 

 milk, this effect being the consequence of the lessened specific 

 gravity resulting from the addition of the water. 



Donne has made the statement, which is borne out by the 

 analyses of MM. Peyen and Peligot, that the globular or 

 buttery element of the milk stands in relation, in the milk of 

 the same species or animal, though not in different species, 

 with the other nutritive ingredients of milk, the cheese and 

 the sugar. 



The analyses referred to are the following : 

 Milk of woman analysed by M. Peyen. 



Butter - 5-16 5-18 5-20 



Sugar and cheese - 7'80 8-10 9'80 

 Milk of asses analysed by M. Peligot. 



Butter - - 1-55 1-40 1-23 1-75 1-51 



Sugar and cheese 10-11 7-97 7'84 8-25 7'80 



Donne, therefore, proposes to estimate the purity and the 

 richness of milk by means of the globular element contained 

 within it. The eye alone will, in some measure, indicate the 

 number of globules contained in the milk; for, since the 

 opacity of milk is due to the presence of the globules, it may 

 be concluded that the milk which is white and opaque is 

 rich in globules, while that which is watery and transparent 

 is poor in the same. 



The microscope, however, is a more certain means of de- 

 termining the number of the globules, although by means of 

 this instrument we can only arrive at an approximative 

 knowledge of their amount. 



