258 PRACTICAL HISTOLOGY. [XXIII. 



and nuclei stain readily with the ordinary dyes, while the clear 

 part does not do so. 



In some mucous glands, e.g. dog, but not in all mucous glands, 

 here and there between the bases of some of these cells, and the 

 basement membrane, are groups of smal], granular, nucleated cells, 

 the group having a somewhat crescentic shape ; they are called 

 demilunes or crescents of Gianuzzi (fig. 250). They stain readily 

 with dyes, and are darkened by osmic acid, and contain two or 

 more nuclei. 



In the discharged or active gland, the acini are smaller, the 

 lumen wider, the clear part of the cell diminished in volume, while 

 the outer part of the cell is wider, and appears to have encroached 

 on the clear part. The nucleus is usually spherical, and placed 

 nearer the centre of the cell. 



In serous or albuminous glands the chief differences are in the 

 cells lining the alveoli. In serous alveoli there is but one layer of 

 cells, and nothing corresponding to the demilunes. The cells are 

 somewhat smaller than mucous cells ; they are more granular, and 

 stain more uniformly with dyes. The nucleus is spherical, and 

 placed nearer the centre of the cell. The differences between 

 active and passive phases are not so marked as in mucous acini. 



During activity the cells become smaller, and the "granules" 

 disappear from the outer part of the cell ; the cells become more 

 sharply defined, while the nuclei are large and spherical. 



N.B. In all cases examine the acini of the glands in the fresh 

 condition. 



A. Mucous Salivary Glands. These must be prepared in 

 several ways. 



Methods. (i.) For the general structure of salivary glands : 



Harden small piece ; for 2 or 3 days in the following mixture : 

 3 parts 90 per cent, alcohol and 2 parts .5 per cent, chromic 

 acid. To see the finer points after staining mount the sections 

 in glycerine (Langley). 



(ii.) Small pieces of a perfectly fresh dog's sub-maxillary gland 

 are placed for an hour in 75 per cent, alcohol, then for five hours 

 in absolute alcohol, which is then changed, and the hardening is 

 completed in fresh absolute alcohol in twenty-four hours. Sections 

 of the unstained gland are apt to fall to pieces, although the small 

 pieces show the structure sufficiently well. A part of the alcohol- 

 hardened gland should be stained " in bulk " in borax-carmine, and 

 cut in paraffin. In this way the relative position of the parts is 

 retained. 



(iii.) Harden very small pieces in i per cent, osmic acid 

 (24 hours) ; wash thoroughly, and complete the hardening in 

 alcohol. 



