20 SCIENCE AND PRACTICE OF DAIRYING. 



The fat globules are not surrounded with a membranous en- 

 velope. Owing to the action of molecular force, the little globules 

 are surrounded by a thin watery covering of serum, and act very 

 much as if they were actually surrounded by a membrane. The 

 influence of the molecular force, manifested in all emulsions, 

 explains why the fat globules in a layer of cream, at ordinary 

 temperatures, do not cohere, and explains why the application of 

 a not inconsiderable force in churning is required to bring them 

 together, and why they offer some resistance to the solvent action 

 of ether. 



As the specific gravity of fat is less than that of milk serum, 

 all the fat globules are under the influence of a force which compels 

 them to ascend to the surface. It has been calculated that this 

 influence acts very rapidly. Thus by keeping a layer of milk 10 to 

 20 cc. in depth for a day and a night, at rest and at ordinary tem- 

 perature, about four-fifths of its total fat comes to the surface. The 

 smallest globules containing the rest of the fat do not experience a 

 motion of their own, because their tendency to rise is no longer 

 sufficient to overcome the opposition offered by the friction of the 

 coagulated casein in which they are enveloped. 



The use of separators has done much to increase the yield of 

 fat. By their aid all the fat may be extracted to within 5 per cent 

 from the milk or cream treated. It is in the highest degree probable 

 that the fat globules, both in milk and cream, are present in a liquid 

 form at ordinary temperatures, and that they are only converted 

 into a solid form by the action of churning. 



The superior digestibility of milk-fat, when partaken of in the 

 form of milk, cream or butter, may be traced to the extreme 

 minuteness of its state of division. 



The composition of the fat of milk does not resemble that of fat 

 obtained from other sources. It is of a much less simple chemical 

 nature than that of other fats. Butter is distinguished from them 

 by its more agreeable taste. The soft condition of butter fat at 

 ordinary temperatures renders it in a special degree suitable for 

 spreading on bread. As is the case with other organic substances 

 of complex composition, it is readily liable to change, is less easily 

 preserved than the other edible fats, and quickly loses its fine flavour 

 under unfavourable circumstances. These special properties of 

 milk-fat render butter the most valued and the most highly prized 

 of all fats. 



