THE PHYSICAL PROPERTIES OF MILK 63 



Kinds of colostrum. Specific gravity. 



Human... .. 1.024-1.034 



Cow's... .... 1.030-1.059 



Goat's 1.028-1.054 



When colostrum stands, the cream often appears in two layers. 

 The upper layer contains the large fat globules, characteristic of 

 colostrum, and is yellow, while the lower layer is composed of 

 true milk-fat. 



Colostrum milk contains a large number of cellular elements, 

 known as colostrum corpuscles, and which have been described 

 before. They disappear five to eight days after parturition, but 

 reappear after the close of lactation and during lactation if the 

 milk is not promptly removed, a thing which may happen when the 

 child is unable to use as much milk as the glands secrete. A large 

 number of corpuscles in the colostrum milk has been considered 

 an indication of profuse milk secretion. 



Besides corpuscles there are mono- and polynuclear leukocytes 

 and lymphocytes in colostrum. 



PROPERTIES OF NORMAL MILK 



Normal milk is an opaque fluid, ranging in color from yellow- 

 ish-white to nearly white, the color due partly to a yellow pigment 

 in the fat, partly to the reflection of light by the fat globules, and 

 also to the colloidal casein. 



The pigment, lactochrome, is associated with the fat and is 

 different both qualitatively and quantitatively in the milk from 

 different animals. It is yellow in cow's milk, for example, and 

 red in human milk. The amount varies in the milk from the 

 same animal, according to the season. In the spring there is 

 more coloring-matter in the fat than later in the summer, and 

 during the winter there is but little, so that butter is more highly 

 colored during the spring than at any other time of the year. In 

 the winter butter is nearly white. The kind of food is probably 

 the cause of this variation. 



According to Palmer and Eckles the pigment of bovine milk- 

 fat is composed of carotin and xanthophyls. Carotin is the more 

 important one of the pigments and belongs to the hydrocarbon 

 group. It is widely distributed in green plants and especially 

 so in grass. Both pigments are contained in the food of cows and 

 are transmitted through the mammary glands to the butter-fat. 

 l$y giving food rich in carotin and xanthophyl the authors were 

 able to intensify the color of the butter-fat. This w r ork explains 

 the heightened color of butter in early summer and the reduction 

 of color in winter, when food poor in pigments is given. 



The light is reflected by the globules in all directions, so that 



