1534 



HUMAN ANATOMY. 



Fig. 1288. 



The serous glands are distinguished by cells which are distinctly granular, 

 generally pyramidal in form, with nuclei situated in the vicinity of the centre. The 

 secretion elaborated by such glands is thin and watery. The general appearance of 

 the cells depends upon the number and size of the granules stored within their cyto- 

 plasm, and changes markedly with the variations of functional activity of the gland. 

 When a serous gland is in a condition of rest, the cells are loaded with secretion, 

 and appear, therefore, larger and coarsely granular. After active secretion, on the 

 contrary, the cells are exhausted and smaller and contain little of their product, often 

 exhibiting differentiation into a clear outer zone, free from granules, and a darker 

 inner zone, next the lumen, in which the granules still remain. 



The mucous glands elaborate a clear, viscid, homogeneous secretion, which, 

 when present in considerable quantity, as during rest, distends the cells, crowding 

 the nuclei to the periphery against the basement membrane, and gives to the glandu- 

 lar epithelium a clear and 

 transparent appearance in 

 marked contrast to the 

 granular character of the 

 elements of a serous Mand. 

 During rest, when loaded 

 and distended with mucoid 

 secretion, the transparent 

 cells possess well-defined 

 outlines, and present a nar- 

 row peripheral zone con- 

 taining the displaced nuclei 

 and granular protoplasm. 

 After prolonged activity the 

 exhausted cells contain rela- 

 tively little mucoid secre- 

 tion, and hence the threads 

 of spongioplasm are no 

 longer widely separated, but 

 lie closely ; in consequence 

 of these changes the cells 

 lose their former transpar- 

 ency and resemble the 

 elements of serous glands, 

 becoming smaller, darker, 

 and more granular than 

 the cells of the quiescent 

 mucous gland. 



The alveoli of mucous 

 glands often contain small 

 crescentic groups of small 

 granular cells lying between 

 °^'""""^ the usual larger clear ele- 



ments and the basement 

 membrane ; these are the 

 crescents of Giamizzi, or demilunes of Heidenhain, the interpretation of which has 

 caused much discussion. The older view regarded the crescents as groups of cells 

 differing from the surrounding ones only in their stage of activity and not in their 

 essential characters, all the cells within the alveolus being of the same nature. The 

 opposite view, advanced by Ebner over a quarter of a century ago, has received sup- 

 port from more recent critical studies by Kiichenmeister, Solger, Oppel, R. Krause, 

 and others, who have shown that the cells composing the crescents differ from the 

 mucus-containing elements, elaborate a special secretion, and are similar to, if not 

 identical with, those filling the alveoli of serous glands. According to these observers, 

 the crescents are groups of serous cells compressed and displaced by the predomi- 

 nating mucous elements, but not excluded from the lumen of the alveolus, as was 



Demilune of 

 serous cells 



Duct 



Mucous cells 



Section of human sublingual gland, showing serous cells arranged as demi- 

 lunes. X 300. 



