556 ANNUAL REPORT OF THE Off. Doc. 



Tile proportions of these constituents of milk-fat vary somewhat 

 and this variation influences the character of the milk-fat. 



(2.) Melting Points of Constituents of Milk-Fat. — In order to under- 

 stand more fully some of the properties of milk-fat. we will briefly 

 notice some of the jnore important properties of the abore-mentio«ed 

 compounds. 



Palmitin has a rather high melting point, 144 degrees F. 



Myristin melts at 129 degrees F. 



Olein and butyrin are liquid at ordinary temperatures. Olein has 

 the important property of being able to dissolve and hold in solu- 

 tion the less easily melting palmitin and myristin, above certain 

 temperatures. 



Palmitin and myristin tend to produce hardness in butter; olein 

 and butyrin, softness. 



(3.) Glycerin is present, chemically combined with acids, in all 

 fats. It forms, on an average, about 12..5 per cent, of pure milk-fat 

 or butter-fat. 



(4.) Physical Properties of Milk-Fat. — Milk-fat, in pure, fresh con- 

 dition, appears at ordinary temperatures as a soft, white to yellowish 

 mass, with mild taste and very slight odor. It easily takes on a 

 granular structure. It melts easily and is lighter than water. 



Our knowledge of the color of milk-fat is very limited. Whether 

 the color is a property of some one of the compounds of milk-fat, 

 or whether it belongs to &ome special substance, mechanically held 

 by the milk-fat, we can not say positively, but the latter supposi- 

 tion is probablj' nearer the truth. It is well established that the 

 color of milk-fat varies with individual cases, with breeds, with ad- 

 vance of lactation and with the food. 



(5.) Milk-Fat m Form of Globules. — Milk-fat is present in milk in 

 the form of very small, transparent globules, too small to be seen 

 by the unaided eye. The sizes most commonly met with are be 

 tween 1-2500 and 1-15000 of an inch in diameter, and the average 

 diameter is not far from 1-10000 of an inch. Some globules are as 

 large as 1-1500 of an inch and some as small as 1-40000 of an inch. 

 The smaller fat-globules are more numerous than the larger ones. 

 In one drop of average milk there are about 150,000,000 fat globules. 



Formerly it was very generally believed, and is still held by some, 

 that fat-globules of milk are surrounded by a membranous covering. 

 In some respects, fat globules behave as if they were enclosed in 

 a membrane. The theory also has been advanced that the fat- 

 globules are surrounded by a semi-solid membrane of slime. With- 

 out going into details to state the reasons, we may accept it as es- 

 tablished beyond reasonable doubt that fat-globules have no special 

 covering, but are simply minute particles of fat floating free in 



