64 PRACTICAL HISTOLOGY. 



SALIVARY GLANDS. 



The salivary glands do not all possess the same structure, nor do corresponding glands in 

 different animals exactly resemble each other ; hence the necessity for examining the various 

 glands of different animals. There are three kinds of salivary glands, which differ in structure 

 and in the nature of their secretion : 



(a] True Salivary Glands as the sub-maxillary gland of rabbits and the parotid of man 

 and some mammals. 



(b] True Mucous Glands as the sub-maxillary glands of cat and dog, and the human 

 sublingual. 



(c] Muco-salivary Glands as the sub-maxillary gland of man and guinea-pig. 



They are all compound tubular glands, made up of branched tubes of varying lengths. 

 The ducts in all are practically the same. They are lobulated and supported by a connective- 

 tissue framework. The nature of the lumen, and the characters of the epithelium lining 

 the alveoli, constitute the chief differences between them. In the true salivary glands (a) the 

 lumen of the alveoli is small, and they are lined by a single layer of low columnar epithelial 

 cells, each with a nucleus near its attached end. These cells are markedly ' granular,' and, 

 as Heidenhain has shown, they vary in appearance during rest and when they are secreting. 

 In true mucous glands (U] there are two kinds of cells one, mucous cells, moderately tall, 

 clear columnar epithelial cells, each with a small nucleus pushed quite out to the membrana 

 propria of the alveolus. They are in fact not unlike goblet-cells, and contain a fine network, 

 whose meshes are filled with mucigen (Heidenhain) ; this yields mucin, which stains deeply 

 with logwood. Outside these, at various parts between them and the alveolar walls, are the 

 ' crescents ' (Gianuzzi), or parietal granular cells. They are small nucleated polyhedral cells. 

 In muco-salivary glands (<:) are found alveoli, which present the characters of true salivary 

 glands, and others exactly like those of mucous glands. 



PREPARATION (a). Place the sub-maxillary glands of a dog and rabbit in absolute 

 alcohol for forty-eight hours. Make transverse sections. Stain with logwood, and mount 

 one in dammar and another in Farrant's solution. This is the best method for a general 

 survey. 



() Harden another gland in chromic acid and spirit mixture for a week, and stain sections 

 with logwood and mount in Farrant's solution. 



(c) Small pieces, the size of half a pea, may be hardened in a quarter per cent, osmic acid, 

 and small pieces teased in glycerine, or sections may be made and mounted in glycerine. 

 It brings out the ' crescents ' very clearly in the mucous glands. 



Sub-maxillary Gland of a Dog. EXAMINATION (L). Observe the lobulated character of 

 the section ; the fibrous capsule sending septa into the gland, and containing blood-vessels, 

 lymphatics, and nerves. Notice the alveoli or gland-substance cut in every direction, and in 

 the interlobular septa here and there a large duct lobar cut into. (H). Study a transverse 

 section of a large lobar duct. Notice the columnar epithelium lining it, with vertical lines due 

 to the longitudinal arrangement of the fibrils, and the nucleus placed about the middle of the 

 cell. Within a lobule may be found sections of an intra-lobular duct, which have a small 

 lumen lined by columnar epithelium. 



Study an Alveolus. Observe the secretory epithelium lining it. The epithelium may be 



