CHAPTEE IV. 



COMPOSITION OF MILK AND ITS BIOLOGICAL, CHEMICAL 

 AND PHYSICAL CHARACTERISTICS. 



There is very little known with, absolute certainty relative to 

 the development of the individual constituents of milk. The 

 theories in this regard are almost entirely hypothetical. It is 

 certain that milk constitutes the specific product of cell activity of 

 the glandular parenchyma, and does not represent a simple trans- 

 udation of the constituents of blood, with a mixture of broken down 

 products of cells (nuclear masses of leucocytes and epithelia, and 

 fatty detritus), nor the fatty breaking down of the epithelium 

 (Reinhardt, Virchow, Skanzoni, Koelliker), nor partial epithelial 

 degeneration of the parts lying adjacent to the lurnen (Heiden- 

 hain), nor transformation of leucocytes and lymph cells (Rauber). 

 None of these is the basic pheonomenon in the formation of milk, 

 but it is due instead to the assimilating activity of the cells, which 

 send their secretion into the lumen of the cell tube (Ottolenghi). 

 A breaking down of cells of course occurs to a greater or lesser 

 extent, in accordance with their increased activity, and therefore 

 the milk contains cells and cell fragments in varied quantities, 

 without this throwing off of cells or breaking down of cells having 

 anything to do directly with the secretion proper. The throwing 

 off of useless material, and its natural replacement by functionat- 

 ing elements are only signs that the organ desires to maintain itself 

 in a condition capable of continued secretion. 



Our attention has previously been directed principally to the 

 functions and activities of the milk gland from a physiological point 

 of view; the morphological condition of the udder and some con- 

 stituents of the secretion have also been noted. In this chapter the 

 chemical qualities of the milk will be considered, as far as this is 

 necessary for the most ordinary conception of these properties. 



The quality of the milk in the broadest sense adjusts itself 

 to the requirements of the young. The milk gland offers it nutri- 

 tive and protective material in a form which most favorably meets 

 the requirements of the off-spring. 



In order to give only a few examples attention should be directed to the estab- 

 lished facts, which show that there exist absolute relations between the time required 



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