Page:Proceedings of the Royal Society of London Vol 69.djvu/368

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It has long been known that the introduction of acid into the duodenum causes a flow of pancreatic juice, and it has been shown recently by Popielski, and by Wertheimer and Le Page, that this flow still occurs after nervous isolation of duodenum and pancreas.

Wertheimer also mentions that the flow can be excited by injection of acid into the jejunum, but not by introduction of acid into the loAver part of the ileum.

These authors conclude that the secretion is a local reflex, the centres being situated in the scattered ganglia of the pancreas, or, in the case of the jejunum, in the ganglia of the solar plexus (Wertheimer).

The secretion excited by introduction of acid into the jejunum cannot be reflex, since it occurs after extirpation of the solar plexus and destruction of all the nervous filaments passing to the isolated loop of jejunum. It also occurs after intravenous injection of O01 gramme atropin sulphate. It must therefore be due to direct excita- tion of the gland cells by a substance or substances conveyed to the gland from the bowel by the blood stream.

The exciting substance is not acid. Wertheimer has shown that injection of 0'4 per cent. HC1 into the blood stream has no excitatory influence on the pancreas.

The secretion must therefore be due to some substance produced in the intestinal mucous membrane under the influence of the acid, and carried thence by the blood stream to the gland.

This conclusion was at once confirmed by experiment.

When the mucous membrane of the jejunum or duodenum is exposed to the action of 0'4 per cent. HC1 a body is produced which, when injected in minimal doses into the blood stream, produces a copious secretion of pancreatic juice. This body, which for the present we may term secretin, is associated with another body with a pronounced lowering effect on the blood pressure. The two bodies are not identical, since acid extracts of the lower end of the ileum produce the pressure- lowering effect, but have no excitatory influence on the pancreas.

The action of the acid is to split off the secretin from a precursor,