THE STKUCTUEE OF THE SALIVARY GLANDS. 



209 



Florence flask, and several of them usually open into one intermediary part of a duct. Each 

 alveolus is bounded by a basement membrane, with a reticulate structure made up of nucleated, 

 branched, and anastomosing cells so as to resemble a basket (D). There is a homogeneous 

 membrane bounding the alveoli in addition to this basket-shaped structure. Immediately out- 

 side this membrane is a lymph-space, and outside this again the network of capillaries is 

 distributed. [The extent to which this lymph-space is tilled with lymph determines the 

 distance of the capillaries from the membrana propria, The interalveolar lymph-spaces com- 

 municate with large lymph-spaces between the lobules, which in turn communicate with 

 perivascular lymphatics around the arteries and veins. ] The lymphatics emerge from the gland 

 at the hilum. 



The secretory cells vary in structure, according as the salivary gland is a mucous 

 [sub-maxillary and sub-lingual of the dog and cat], a serous [parotid of man and 

 mammals, and sub-maxillary of rabbit], or a mixed gland [human sub-maxillary 

 and sub-lingual]. 



Mucous Acini, The secretory cells of mucous glands, and the mucous acini of mixed glands 

 (fig. 156), are lined by a single layer of " mucin cells " (fig. 155, B,'c), which are large cells dis- 

 tended with mucin, or with a hypothetical 

 substance, mucigen, which yields mucin. The 

 mucin cells are more or less spheroidal in 

 shape, clear, shining, highly refractive, and 

 nearly fill the acinus. The flattened nucleus 

 is near the wall of the acinus. Each cell has a 

 fine process which overlaps the fixed parts of 

 the cells next to it. Owing to the body of 

 each cell being infiltrated with mucin, these j 

 cells do not stain with carmine, although the 

 nucleus and its immediately investing proto- 

 plasm do. Another kind of cell occurs in the 

 sub-maxillary gland of the dog. It forms a 

 half-moon-shaped structure lying in direct 

 contact with the wall of the acinus (Gianuzzi). 

 Each "half-moon" or "crescent" consists 

 of a number of small, closely packed, angu- 

 lar, highly albuminous cells with small oval 

 nuclei, which, however, are separated only 

 with difficulty. Hence, Heidenhain has called 

 them "composite marginal cells" (B, d). 

 They are granular, darker, devoid of mucin, 

 and stain readily with pigments. [In the 

 sub-maxillary gland of the cat, there is a 



complete layer of these " marginal " carmine- -gig 156 



staining cells lying between the mucous cells _ ,. . , * . ^ 



and the membran? propria. ] Section of a human sub-maxillary gland. On 



[Serous Acini. In true serous glands the left is a group of serous alveoli, and on the 

 (parotid of man and mammals) and in the n g nt a g rou P of mucous alveoli, 

 serous acini of mixed glands, the acini are lined by a single layer of secretory columnar finely- 

 granular cells, which in the quiescent condition completely fill the acinus, so that scarcely any 

 lumen is left. Just before secretion, or when these cells are quiescent, Langley has shown that 

 they are large and filled with numerous granules, which obscure the presence of the nucleus. 

 As secretion takes place, these granules seem to be used up or discharged into the lumen ; at 

 least, the outer part of each cell gradually becomes clear and more transparent, and this con- 

 dition spreads towards the inner part of the cell.] 



[In the mixed or muco-salivary glands (e.g., human sub-maxillary) some of the alveioli are 

 mucous and others serous in their characters, but the latter are always far more numerous, and 

 the one kind of acinus is directly continuous with the others (fig. 156).] 



143. HISTOLOGICAL CHANGES DURING THE ACTIVITY OF THE 

 SALIVARY GLANDS. [The condition of physiological activity of the gland-cells 

 is accompanied by changes in the histological characters of the secretory cells. 

 Changes in serous glands have been carefully studied in the parotid of the rabbit, 

 but the appearances vary somewhat, according as the glands are examined in the 

 fresh condition or after hardening in various reagents, such as absolute alcohol. 

 When the gland is at rest, in a preparation hardened in alcohol, and stained with 

 carmine, the cells consist of a pale, almost uncoloured substance, with a few fine 







