752 PHYSIOLOGY 



almost entirely to the inner margin of the cell. Activity is thus 



associated certainly with a discharge of granules, and probably 



with some increased building up of protoplasm. We may regard the act 



f secretion as determined by the alteration of the granules and their 



discharge, together with water and salts, to form the specific secretion 



the gland. During rest the granules are re-formed by precipitation 



m or modification of the protoplasm surrounding the nucleus We 



have evidence that although the granules form the secretion, they 



represent, not the secretion itself, but a precursor of some at any rate 



of its constituents. Thus if acetic acid be added to the saliva obtained 



FIG. 328. Sub-maxillary gland of rabbit. (ScHAFER after E. MUM.ER ) 



6 fdfch? S T U t, are k different functio ^l states : a, a loaded cell ; 

 'charged cell; c, a secretory canaliculus penetrating into a cell. 



from the sub-maxillary gland, the mucin is precipitated as threads 

 If the granules in the secreting cells also consist of mucin 

 we should expect acetic acid to have a coagulating effect upon them 

 nnd, on the contrary, that on allowing acetic acid to flow over 

 a section of the fresh gland the granules at once swell up and burst 

 We must regard these granules therefore, not as mucin, but as a pre-' 

 cursor of mucin, mucigen. The effect of ordinary hardening reagents 

 such as dilute alcohol up to 70 per cent, or Miiller's fluid, is to cause 

 these granules to swell up so that the cells become filled with a mass 

 iucin giving the typical hyaline appearance of ordinary sections of 

 e glands. In the case of the serous gland the granules (Fig. 328) are 

 apparently protein in nature. Where ptyalin is a constituent of 

 3 saliva we are probably justified in assuming that it is contained 

 to pre-formed or more probably as a precursor in the granules 

 fn the glands of the stomach we have evidence that the granules are 

 pepsm-the characteristic ferment of gastric juice-but a pre- 

 this substance, namely, pepsinogen. It is very customary 



