36 MILK 



the nucleus, and with this ring the nucleus" moves toward that 

 part of the cell which faces the lumen of the milk ducts and finally 

 appears in it, leaving the cell behind. After the Nissen corpuscle 

 has been discharged the- cell regenerates and resumes activity. 

 Some observers beheve that the Nissen corpuscles are the origin 

 of casein, while others argue that they are not formed in sufficient 

 number to account for the amount of casein present in milk. 



There is possibly some connection between leukocytes and milk 

 secretion, and while this view is sometimes advanced it has not 

 found much support. There is really a constant influx of leuko- 

 cytes into the secretion, especially during the colostrum period and 

 at the close of lactation. The significance of leukocytes is not 

 understood, but has given rise to the idea, mentioned in another 

 connection, that milk secretion is a pathologic process or at least 

 comparable to one. 



At the present state of our knowledge — which is very rudimen- 

 tary — the most acceptable idea about milk secretion is that the 

 cells of milk glands are not destroyed, but that since milk secretion 

 is an intensive process the cells are unusually active, age rapidly, 

 and therefore may degenerate (Ottolenghi). 



Relation of Colostrum to Secretion 



During the last days before and the first days after parturition 

 the secretion is different from normal milk in chemical, physical, 

 and biologic properties. This secretion is the colostrum milk — 

 a yellowish, sticky fluid, rich in protein and containing extra- 

 ordinarily large numbers of cellular elements — commonly called 

 colostrum corpuscles. The function of these cells has been the 

 subject of much speculation, but, as stated above, the view held 

 at present is that they are not concerned in milk secretion. They 

 are regarded rather as being actively engaged in reconstructing 

 tissues to restore the condition preceding actual lactation. For 

 this reason colostrum cells are present immediately before and 

 after lactation has commenced and -at its close. Corpuscles have 

 actually been seen in sections of mammary glands after milk secre- 

 tion has ceased. They probably act on the remnants of milk 

 constituents and render them available as food for the maternal 

 system (Czerny). This function is similar to the phagocytic ac- 

 tion in pathologic processes, and the immigration of leukocytes 

 during milk secretion has given rise to the comparison of milk to 

 pus. Through their phagocytic action the ingested milk constit- 

 uents are prepared for reabsorption by the system. The presence 

 of these cells, therefore, indicates an incomplete condition account- 

 ing for their appearance "both at* the commencement and the close 

 of lactation. 



