LACTATION 



589 



In the .seeretmy cells (if the lactating maiumary gland an active 

 and a resting condition can lie distinguished. In the latter the 

 Inmina of the alveoli are wide, and the cells of the lining eiiitheliuni 

 form a single fiat layer with centrally situated nuclei. Tn the active 

 condition tlie epithelial cells are long and columnar, and jiroject into 

 the lumina, and some of them have two nuclei. 



In these cells numliers of granules and ghjlmles accumulate, the 

 former being pniliahh' of a protein nature, and the latter of a fatty 

 composition. (Iradually the alveoli Jiecome chargeil with a fluid 

 containing detached cells and fatty glolmles. The detached cells are 

 usually filled with granules, staining with osniie acid and seemingly 





Fig. 102. — Section of mannnarv gland of \yonian. (From Sharpey 

 SL'hafei', after de .Sinetv.) 



f', Lobule of gland ; /<, acini lined by cubical epithelium ; s duct ; 

 ?, connective tissue. 



identical with the colostrum corpuscles which have been (ibserved to 

 occur in milk in the first few days after parturition, and occasionall)' 

 also at other times. These colostrum corpuscles have been seen to 

 exhibit amodjoid movements, and so are proliably leucocytes which 

 have wandered into the lumina of the alveoli.^ The secretory fluid 

 also contains cells which are supposed to have been detached from 

 the epithelium, liut, as will lie seen presently, there is some doubt 

 regarding this point. 



The alveoli secrete milk during lactation, not merely \\hile 

 suckling is going on, but also at other times, so that milk tends to 

 collect in the ducts and especially in the reservoirs. It has been 



1 Sliarpey Schafer, "The Mechanisnt of the Secretion of Milk,'' Text-Bonk 

 of Physiohx/ii, aoI. i., Edinburgh, 1898. 



