174 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



striction of the pancreas prevents the action of the secretory nerves upon it. 

 Thus stimulation of the sympathetic gives usually no effect upon the secretion, 

 because vaso-constrictor fibres are stimulated at the same time, but if the sym- 

 pathetic nerve is cut five or six days previously, so as to give the vaso-con- 

 strictor fibres time to degenerate, stimulation will cause, after a long latent 

 period, a distinct secretion of the pancreatic juice. 



Accepting the theory of secretory and trophic fibres proposed for the sali- 

 vary glands, the experiments upon the variations in pancreatic secretion follow- 

 ing upon stimulation of the vagus and sympathetic respectively seem to indi- 

 cate that in the sympathetic trophic fibres are more abundant, and in the vagus 

 the secretory fibres proper. The long latent period elapsing between the time 

 of stimulation and the effect upon the flow is not easily understood. The 

 authors quoted give no satisfactory explanation of this curious fact, but sug- 

 gest that it may be due to the presence of definite inhibitory fibres to the 

 gland, which are stimulated simultaneously with the secretory fibres and thus 

 hold the secretion in check for a time. No independent proof of the presence 

 of inhibitory fibres is furnished. 



Histological Changes during Activity. The morphological changes in 

 the pancreatic cells have long been known and have been studied satisfac- 

 torily in the fresh gland as well as in preserved specimens. The general 

 nature of the changes is the same as that described for the salivary gland, 

 and is illustrated in Figures 75, 76, and 77. If the gland is removed from 

 a dog which has been fasting for about twenty-four hours and is hardened 

 in alcohol and sectioned and stained, it will be found that the cells are filled 

 with granules except for a narrow zone toward the basal end, which is marked 

 off more clearly because it stains more deeply than the granular portion (Fig. 

 75). If, on the contrary, the gland is taken from a dog which had been fed 



FIG. 75. Pancreas of the dog during hunger ; preserved in alcohol and stained in carmine 



(after Heidenhain). 



six to ten hours previously, the non-staining granular zone is much reduced in 

 size, while the clearer non-granular zone is enlarged (Fig. 76). The increase 

 in size of the non-granular zone does not, however, entirely compensate for 



