SECRETORY FUNCTIONS IN HUMAN PLACENTA 515 



of regression, who could explain the reason why this kind of 

 'regressive' cell actually appears in so high a degree within the 

 tissues of the placenta and the decidua at a certain period of 

 pregnancy, and especially in the first half of pregnancy when 

 the tissues should grow in a most vigorous manner? There- 

 fore, I am confident that not only is it wrong to deem such 

 vacuolar formations a death phenomenon of the cell, but also 

 they should rather be taken for a quite significant phenomenon 

 which shows a certain function of the cell concerned. And, 

 as regards the actual existence of such a function, I am in- 

 clined to assert from their closest resemblance to the structures of 

 many other glandular cells, as a result of my histological ob- 

 servations, that a secretory function is existent in these kinds 

 of cells. However, as the problem is of such a provisional 

 character I will, for the present, reject all hasty assertions, but 

 instead will consult literature widely and make general reference 

 to the previous interpretations of many authors on the struc- 

 tures and secretory processes of the various glandular cells in 

 the organs in which secretory functions are definitely known, 

 so that the most deliberate considerations can be given my 

 histological observations and their functional significance, which, 

 being compared and discussed under impartial criticism, it is 

 hoped, will help toward making the original nature of the func- 

 tions clear. 



Since the relations between glandular histology and secre- 

 tory functions were early dwelt upon by R. Heidenhain ('68, 

 '75, '80) with his penetrating eyes, the subject has aroused the 

 interest of many excellent physiologists and histologists, and 

 the studies of the subject have since followed so quickly one 

 after the other, that it would be difficult to enumerate them 

 here. The following are the principal authors who have studied 

 the subject, and the materials chosen by them for investigations 

 were chiefly pancreas, salivary glands, gastric glands, lacrimal 

 glands, skin glands, and pelvic glands, all of which are usually 

 known as representative glands in many kinds of animals classed 

 above the amphibians : Schultze, Fr. E., '64 and '67; Langhans, 

 '69; Pfliiger, '71; Schwalbe, '71; Ebner, '73; Nussbaum, '78 to '82; 



