58 INTERNAL SECRETION 



effect, which, however, is not confined to the vagus, stimulation 

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

 effect, may be regarded (in the absence of any proof that the 

 result is due to reflex constriction of the pancreatic and local 

 vessels 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. But if so, then we must 

 regard the secretion of pancreatic juice as closely resembling 

 that of saliva, inasmuch as it is called forth by a reflex act. Yet 

 it is stated that, unlike the case of saliva, the secretion of 

 pancreatic juice continues after all the nerves going to the gland 

 have been divided, an operation which would do away with the 

 possibility of reflex action. Such an experiment, however, 

 cannot be regarded as decisive, since it is almost impossible to 

 be sure of dividing all the nerves." 



It is interesting to note how the one single observation 

 (secretion after severance of all nerves), which at this period 

 had to be opposed to the theory of reflex stimulation, was dealt 

 with by Michael Foster. At this date, then, and for some time 

 later the prevailing view was that the flow occurring when the 

 acid chyme passed into the duodenum is due to the action of a 

 reflex arc ; but the observations of Bernard, Heidenhain and 

 Pavlov, incorporated in the above account by Foster, were 

 inconclusive, and the results obtained in different experiments 

 were by no means constant. In more recent years Pavlov and 

 his pupils have multiplied ingenious experiments and developed 

 a wonderful technique, have struggled hard to reconcile the 

 conflicting statements of different observers, and with infinite 

 ingenuity have sought to establish on a firm basis the theory of 

 nervous action. In searching for the channels of the reflex, 

 Pavlov showed that, if certain precautions be taken, one can 

 bring about a flow of pancreatic juice by stimulating the vagus 

 HI splanchnics. 



A great step in advance was made by Popielski and by 

 Wertheimer and Le Page. These observers proved conclu- 

 sively that introduction of acid into the duodenum still excites 

 pancreatic secretion after section of both vagi and both 

 splanchnic nerves or destruction of the spinal cord, or even 

 after ri.inplete extirpation of the solar plexus. Thus it was 



