SECRETION OF PANCREATIC JUICE AND OF BILE. 



287 



nervous mechanism. The details of this mechanism have, however, not as 

 yet been satisfactorily worked out. 



The pancreas derives its nerves, which reach it along its bloodvessels, 

 from the solar plexus of the splanchnic system, but the ultimate origin of 

 the fibres have not been traced out ; some of them, however, certainly come 

 through the plexus from the right vagus. 



Stimulation of the medulla oblongata, or of the spinal cord, will call forth 

 secretion in a quiescent gland, or increase a secretion already going on. 

 From this we may infer the existence of a reflex mechanism, though we 

 cannot as yet trace out satisfactorily the exact path of either the afferent or 

 the efferent impulses ; all we can say is, that the latter do not reach the 



FIG. 88. 



2j 3| 4 I 5 I 6 I 7 |8 I 9 1 10 I 111 12 1 13 I H 1 15 |lG i 1 I 2 I 3 I 4 I 5 I 6 I 7 I 8 I 9 llO 



Diagram illustrating the Influence of Food on the Secretion of Pancreatic Juice. (N. 0. 

 Bernstein.) The abscissae represent hours after taking food ; the ordinates represent in c.c. the 

 secretion in ten minutes. A marked rise is seen at B immediately after food was taken, with a 

 secondary rise between the fourth and fifth hours afterward. Where the line is dotted the obser- 

 vation was interrupted. On food being again given at C, another rise is seen, followed in turn 

 by a depression and a secondary rise at the fifth hour. A very similar curve would represent the 

 secretion of bile. 



pancreas by the vagus, since stimulation of the medulla is effective after 

 section of both vagi. 



A secretion already going on may be arrested by stimulation of the cen- 

 tral end of the vagus, and the stoppage of the secretion, which has been 

 observed as occurring during and after vomiting, is probably brought about 

 in this way. This effect, which, however, is not confined to the vagus, stimu- 

 lation of other afferent nerves, such as the sciatic, producing the same effect, 

 maybe regarded (in the absence of any proof that the result is due to reflex 

 constriction of the pancreatic bloodvessels unduly checking the blood-supply) 

 as an inhibition of a reflex mechanism at its centre in the medulla, or in 

 some other part of the central nervous system, much in the same way as 

 fear inhibits at the central nervous system the secretion of saliva following 

 food in the mouth ( 196). But if so, then we must regard the secretion of 

 pancreatic juice as closely resembling that of saliva, inasmuch as it is called 



