SECRETION. 233 



vasoconstriction 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 sympathetic nerve is cut five or six days previously, so as to give 

 the vaso-constrictor fibres time to degenerate, stimulation will cause, after a 

 long latent period, a distinct secretion of the pancreatic juice. A similar 

 result may be obtained from stimulating the undegenerated nerve if mechani- 

 cal stimulation is substituted for the electrical. 



The long lateut period elapsing between the time of stimulation and the 

 effect upon the flow is not easily understood. The authors quoted do not 

 give an entirely satisfactory explanation of this curious fact, but suggest 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. The existence of inhibitory fibres is rendered 

 probable by several interesting experiments, for an account of which the 

 original sources must be consulted. 1 



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 chauges is the same as that described for the salivary gland, 

 and is illustrated in Figures 58, 59, and 60. 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. 

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



Fig. 58.— Pancreas of the dog during hungei : preserved in alcohol and stained in carmine 



(after Heidcnlmin). 



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

 size, while the clearer non-granular zone is enlarged (Fig. 59). The increase 

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



1 Pawlow: Die Arbeit der Venlaiuiv/jxiiriisen, p. 78, Wiesbaden, 1898. 



