ABOUT MILK IN GENERAL. 377 



Ayrshire, the Jersey and the Dutch, those large black-and- 

 white cattle from Holland. Although these discoveries are 

 probably of universal application, yet in this paper the con- 

 clusions will bo confined to the results of my own examina- 

 tions, which have been fairly complete with reference to the 

 Ayrshire and Jersey milks, but more limited with the Dutch. 



Milk in General. 



The globules in milk are of varying sizes, some so small as 

 to appear as granules under a mngnifj'ing power of 800 diam- 

 eters, others very much larger. The small globules, — for an 

 increased power has invariably defined them as such, — I shall 

 for convenience term granules. As 2Y5o¥ ^'^^"^^ ^*' ^^ith my 

 micrometer, a convenient division, I shall speak of all glob- 

 ules less than this fissure as oranules, and all alcove as glob- 

 ules. Every sample of milk I have yet examined has shown 

 these granules, yet in some milks much more abundant than in 

 others. In the skim-milk the granule has always been readily 

 found, even when rare in the cream. These glol)ules being 

 composed of various fats surrounded by a pellicle, are inti- 

 mately' mixed with the milk as it comes from the cow, but 

 their position soon becomes changed as they come under the 

 influence of gravity ; they rise to the surface of the milk to 

 form cream. As the weifjht of the coverino- to the fat ji^lob- 

 ule, which is heavier than water, increases proportionately to 

 the volume of fat as the sphere is diminished in diameter, the 

 various globules show difference in physical action. When 

 the weight of the covering is just or nearly sufficient to bal- 

 ance the low specific gravity of the fats, the globules remain 

 nearly stationary in the fluid; w'.:eii, however, the globule 

 is large, the specific gravity of the mass is so much less than 

 that of the fluid in which it occurs, that it speedily reaches the 

 surface. It therefore fo.lows that the upper layer of the 

 cream is composed of larger globules than the lower layer, 

 or, giving expression to a general f\ict, the further you go 

 from the surface of milk which has been at rest the smaller 



the milk-globule. 



Experiment T. 



Three drops of milk were taken from a vessel containing 



milk which had been undisturbed for fourteen hours : — 



48 



