352 A MANUAL OF PHYSIOLOGY 



abundance, can be obtained, without the introduction of any food 

 into the stomach, either by the process of sham feeding (p. 374) or 

 by psychical stimulation of the gastric glands when food is shown 

 to an animal. 



Changes in Mucous Glands during Secretion. In the mucous 

 salivary and other mucous glands similar, but apparently more 

 complex, changes occur. During rest the cells which line the 

 lumen may be seen in fresh, teased preparations to be filled with 

 granules or ' spherules.' After active secretion there is a great 

 diminution in the number of the granules. Those that remain 

 are chiefly collected around the lumen, although some may also 

 be seen in the peripheral portion of the cell ; and there is no very 

 distinct differentiation into two zones. That a discharge of 

 material takes place from these cells is shown by their smaller 

 size in the active gland. That the material thus discharged is not 



FIG. 141. Mucous CELLS (FROM SUBMAXILLARY OF DOG) IN REST 

 AND ACTIVITY (LANGLEY). 



A, B, fresh ; A', B', after treatment with dilute acetic acid ; A", B", alveoli 

 hardened in alcohol and stained with carmine. A, A', and A" represent the 

 loaded ; B, B', and B", the discharged condition. 



protoplasmic is indicated by the behaviour of the cells to proto- 

 plasmic stains such as carmine. The resting cells around the 

 lumen stain but feebly, in contrast to the deep stain of the 

 demilunes, while the discharged cells take on the carmine stain 

 much more readily. Further, when a resting gland is treated 

 with various reagents (water, dilute acids, or alkalies), the 

 granules swell up into a transparent substance identical with 

 mucin, which fills the meshes of a fine protoplasmic network. 



In ordinary alcohol-carmine preparations only the network and 

 nucleus are stained ; the nucleus, small and shrivelled, is situated 

 close to the outer border of the cell. When a discharged gland is 

 treated in the same way there is proportionally more ' proto- 

 plasm ' (or ' bioplasm ') and less of the clear material, what 

 remains of the latter being chiefly in the inner portion of the 

 cell, while the nucleus is now large and spherical, and not so 

 near the basement membrane (Fig. 141). 



