XX] SALIVARY GLANDS 163 



This cork replaces the first cork in the bottle, it is left for a day. 

 The pieces of tissue are then placed in absolute alcohol for a day or 

 longer ; imbedded in paraffin and cut. The sections are stained for 

 a day in methylene blue in 75 p.c. alcohol, and mounted in balsam. 



If the sections are placed in alcohol about 70 p.c. or any lower 

 percentage, the mucous granules swell up, they may then cohere, or 

 they may be only pressed together into an apparently continuous mass, 

 returning to the spherical form when placed once more in strong 

 alcohol ; in the latter case they should be stained in aqueous solutions 

 of methylene blue. 



They are also more or less preserved by hardening a small piece 

 of gland in absolute alcohol, imbedding in paraffin, and staining the 

 section on the slide in alcoholic stains. 



Variations of mucous glands. The orbital gland of the dog is best 

 for showing a typical mucous gland, the sub-maxillary gland of the 

 dog has more serous cells, that of the cat still more. A few mucous 

 alveoli are generally present in the parotid of the dog. 



Varieties of serous glands. In some glands more than one kind of 

 secretory cell is present. Thus in a piece of fresh sub-maxillary 

 gland of the rabbit, the ends of the ductules and first cells of the 

 alveoli (transition cells) have distinct granules, whilst the rest of the 

 alveolar cells are only faintly granular. In sections of osmic acid 

 hardened gland, the transition cells are stained darker than the rest. 

 In the serous part of the sub-maxillary gland of the rat, curving tubes 

 with large granules will be seen amongst the mass of faintly granular 

 alveoli ; they are easily preserved by reagents and stained. 



If a resting and an active serous gland be preserved in 1 p.c. osmic 

 acid, and the sections compared, it will be seen that cells of the 

 active gland stain a darker tint than those of the resting ; the granules 

 are not usually preserved by osmic acid so that the distinction of 

 zones in the active gland, readily seen in the fresh state, is not usually 

 seen in the sections. 



The sub-lingual gland differs from the typically mucous and from 

 the typically serous glands. It is more obviously tubular, some of 

 the tubes are entirely mucous, some entirely serous, some contain 

 both mucous and serous cells; some have cells with a mucin inner 

 and proteid outer zone. 



Glands both serous and mucous not uncommonly contain some 



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