MAMMAEY SECEETION. 



625 



The weight of the milk-gland is not more than 4.8 kilos, with 24.2 per 

 cent, solids, including all the glandular tissue (vessels, capsule, connective 

 tissue, etc.), or 1.16 kilos solids. Consequently, the gland must renew 

 itself 2.09 times dail}* to furnish this amount of organic matter if derived 



M 



ms 



FIG. 260. SECTION OP THE UDDER AND NIPPLE OF THE Cow. (ThanTicffer.) 



Ma, gland-substance : B, nipple; ms, acini of gland; tj, milk-ducts ; C, milk-cistern ; r, folds in wide 

 milk-ducts ; z, section of sphincter muscle ; kb, external skin ; ki, narrow milk-duct in the nipple. 



solety from the secreting cells. This would, however, require an incred- 

 ibly rapid cell growth, and we are compelled to assume that although the 

 growth and disappearance of the secreting cells is of the greatest im- 

 portance in furnishing the organic constituents of the milk, these sub- 

 stances are not derived solely from the breaking down of the cells, but 



40 



