THE SECRETION OF THE DIGESTIVE JUICES 375 



the blood or lymph. It was pointed out in favour of this view that 

 when, instead of sodium chloride, sodium bromide is given in the food, 

 the hydrochloric acid in the stomach is to a large extent replaced by 

 hydrobromic acid. And it was argued that this cannot be due to the 

 decomposition of the bromide by hydrochloric acid, since it occurs in 

 animals deprived for a considerable time of salts, and in ' salt-hunger ' 

 the stomach contains no acid (Koeppe). It may be, however, that 

 even in ' salt-hunger ' the presence of sodium bromide in the stomach 

 stimulates the secretion of hydrochloric acid, which then decomposes 

 the bromide, with the formation of hydrobromic acid. The sodium 

 chloride formed in the double decomposition might be re-absorbed, 

 and the stock of chlorides in the blood remain undiminished. It is in 

 any case a decisive objection to this now defunct theory that a copious 

 secretion of gastric juice, containing hydrochloric acid in abundance, 

 can be obtained, without the introduction of any food into the stomach, 

 either by the process of sham feeding (p. 395) 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 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 sub- 

 stance 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 ' protoplasm ' (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. 158). 



Everything, therefore, points to the granules in what we may now 

 call the mucin-forming cells as being in some way or other precursors 

 of the fully-formed mucin ; manufactured during ' rest ' by the proto- 

 plasm and partly at its expense, moved towards the lumen in 

 activity, discharged as mucin in the secretion. It has been asserted 

 that not only is the protoplasm lessened in the loaded cell and re- 

 newed after activity, but that many of the mucigenous cells may be 

 altogether broken down and discharged, their place being supplied 

 by proliferation of the small cells of the demilunes. This conclusion, 

 however, is not supported by sufficient evidence. The cells of the 

 crescents contain fine granules, but none which can be changed into 



