COMPOSITION OF MILK. 



615 



cumstances only occurs after parturition, if we except the 

 slight secretion which takes place in the latter months of preg- 

 nancy, is effected by the epithelial cells lining the ultimate 

 follicles of the mammary gland. The process does not differ 

 from secretion in glands generally (see p. 321), and need not 

 here be particularly described. 



Under the microscope, milk is found to contain a number 

 of globules of various size (Fig. 247), the majority about 



$* 



Microscopic appearance of human milk with an intermixture of colostric 

 corpuscles. 



an nc n diameter. They are composed of oily 

 matter, probably coated by a fine layer of albuminous material, 

 and are called milk-globules; while, accompanying these, are 

 numerous minute particles, both oily and albuminous, which 

 exhibit ordinary molecular movements. The milk which is 

 secreted in the first few days after parturition, and which is 

 called the colostrum, differs from ordinary milk in containing 

 a larger quantity of solid matter ; and under the microscope 

 are to be seen certain granular masses called colostrum-cor- 

 puscles. These, which appear to be small masses of albumin- 

 ous and oily matter, are probably secreting cells of the gland, 

 either in a state of fatty degeneration, or, as Dr. Gedge re- 

 marks, old cells which in their attempts at secretion under the 

 new circumstances of active need of milk, are filled with oily 

 matter ; which, however, being unable to discharge, they are 

 themselves shed bodily to make room for their successors. 



The specific gravity of human milk is about 1030. Its 

 chemical composition has been already mentioned (p. 200). 



