An introduction to the study of secretion / by Swale Vincent.

  • Vincent, Swale, 1868-1934.
Date:
1924
Catalogue details

Licence: In copyright

Credit: An introduction to the study of secretion / by Swale Vincent. Source: Wellcome Collection.

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    food has been taken, does not reach its maximum till two or three hours have elapsed. This is at a time when the greatest quantity of food is passing from the stomach into the duodenum. As to the precise causal relationship between the passage of food into the duodenum and the flow of pan- creatic secretion, there is still much to be learnt. M. Foster in his text-book of 1889 says : “ Stimulation of the medulla oblongata or of the spinal cord will call forth secretion in a quiescent gland, or increase a secretion 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 pancreas by the vagus, since stimulation of the medulla is effective after the section of both vagi. “ A secretion already going on may be arrested by stimu- lation of the central 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 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.” We have seen in the case of the submaxillary gland, that a secretion (“ paralytic ”) will flow when the chorda has been cut, and it is conceivable that the same kind of thing might