28 SECRETION 



from those entirely mucous to those entirely albuminous. 

 The demilunes of Heidenhain in mucous glands are albuminous 

 cells. The two types of cells differ not only histologically, 

 but also in the character of their products. The secretion from 

 albuminous cells contains, besides enzymes, water, salts, and 

 albumin, while that from mucous cells contains mucin, which 

 makes it stringy and viscid. 



The activity of secretory cells is well shown by the salivary 

 glands. During secretion the granules which are present 

 gradually disappear from the outer side of the cells, and a 

 clear non-stainable material is substituted. The nuclei become 

 more spherical and lie nearer the centre of the cell body, which 

 shrinks in size. The granular material is apparently used up 

 in the formation of. the secretion, and since the enzymes formed 

 are specific substances, the former are taken to be their source 

 and designated as zymogen granules. The forerunner of ptyalin 

 is called ptyalinogen; of pepsin, pepsinogen, etc. 



The pressure in the duct of the submaxillary has been observed 

 at 190 mm. Hg, while the blood pressure in the carotid at 

 the time was but 112 mm. Hg. The question of the amount 

 of heat given off during the activity of the gland is still un- 

 settled. Ludwig and Spiess originally determined the saliva 

 to be 1 warmer than the blood in the carotid. Heidenhain, 

 by the thermo-electric method, found the difference to become- 

 greater on stimulation of the sympathetic. The electrical 

 changes in glands are analogous to the action currents in 

 muscles. The current may be ingoing, outgoing, or diphasic 

 in character. 



Nervous Factors. The salivary glands have a cranial and a 

 sympathetic nerve supply, whose influence may be illustrated 

 by the results obtained from the submaxillary of the dog. 

 When the chorda tympani, whose fibers are cranial in origin, 

 is stimulated with weak induction shocks, the saliva obtained 

 is relatively abundant, thin, and watery, containing not more 

 than 1 to 2 per cent, of solids. The gland becomes redder in 

 color, the veins are distended, and the blood shows a distinct 

 pulse, indicating a dilatation of the small arteries and that 

 the chorda tympani carries dilator fibers. Stimulation of the 

 sympathetic fibers produces a scanty secretion, which is thick 

 and turbid, and may contain 6 per cent, of solids. The gland 



