412 MUCOUS GLANDS. [BOOK n. 



readily with the usual dyes; the rest of the cell-body consists of a 

 transparent material, which does not stain readily, and which occu- 

 pies the spaces or meshes of a very delicate meshwork continuous 

 apparently with the staining protoplasmic cell -substance around 

 the nucleus, and with a thin sheet of similar material forming the 

 wall of the cell. This transparent material is either mucin, which 

 we have seen to be a conspicuous constituent of submaxillary 

 saliva (in the dog), or a substance which can be easily converted 

 into actual mucin, that is to say an antecedent of mucin; hence 

 the name 'mucous cell.' A resting or loaded mucous cell then 

 consists largely of mucin (or its antecedent) lodged in the meshes 

 of the protoplasmic cell-substance which over the greater part 

 of the cell exists, in a hardened gland at any rate, as a delicate 

 meshwork or reticulum, but is gathered into a compact mass in 

 a small area immediately around the nucleus. 



In many alveoli may be seen, generally lying on the basement 

 membrane between the diverging bases of the mucous cells, other 

 cells which, generally small, differ from the mucous cells inasmuch 

 as the whole cell stains readily with staining reagents. They often 

 assume a half-moon shape, and are spoken of as demilune cells. 

 They appear to be albuminous cells (of which we shall speak 

 presently), occurring sparsely among mucous cells and compressed 

 by these. 



In the ' discharged,' or as it is often called the ' active ' phase, 

 the mucous cell has a different appearance, especially if the 

 activity of the gland has been great. The cell is now smaller, 

 and thus gives rise to a more distinct lumen in the alveolus, 

 a larger portion of the cell stains, especially on the outer side, 

 and sometimes the whole cell stains ; the nucleus, now spherical 

 even in hardened specimens, occupies a more central position. 

 The transparent, non-staining mucin has in large part or wholly 

 disappeared, its place has been taken by ordinary staining proto- 

 plasmic cell- substance, and the distinction between the demilune 

 cells and the proper cells of the alveolus is much less distinct. 

 We shall presently have to discuss the nature and meaning of this 

 change from the loaded to the discharged cell. 



217. A small duct of the submaxillary gland, even when cut 

 transversely in the section so as to present like many alveoli a 

 circular outline, has an appearance very different from that of 

 an alveolus. The duct is lined by a single layer of epithelium, 

 but these are slender, narrow, columnar cells leaving in the centre 

 a relatively wide lumen, and the outside of the duct is not so 

 sharply denned by a conspicuous basement membrane as is the 

 case in an alveolus. Each cell, which bears an oval nucleus placed 

 vertically in the cell at about the middle but rather nearer the 

 base, consists of a protoplasmic cell-substance which on the inner 

 side of the nucleus towards the lumen has no special features, but 

 on the outside, towards the basement membrane or connective 



