The influence of the intestinal contents upon the movements of the gut was discussed as long ago as 1750 by Foelix.[10] Among the later authors to treat of this subject is Bokai. In addition to indigestible and irritating substances taken in with the food, there are certain substances ordinarily formed in the intestine by decomposition which cause peristaltic movements. Among these are CO_{2}, CH_{4}, and H_{2}S. All of these gases which are more or less constantly formed help in keeping up the normal movements of the intestine. Certain faecal constituents have also the same effect. Bokai mentions among these a number of organic acids--lactic, succinic, butyric, formic, propionic, acetic, caproic, and caprylic acids. There is no doubt also that the salts taken in with the food exert a considerable influence. The intestine is to some extent also under the influence of extrinsic nerves. As shown by Pflüger,[11] the splanchnic nerves exert an inhibitory action on the intestine, so that their section causes intestinal movements and their stimulation brings about a cessation of peristalsis. This has been ascribed by some authors to the vasomotor action of the nerves. Concerning the action of the vagus there has been difference of results. Many experimenters have found that stimulation of this nerve causes contractions of the intestine. Others have obtained no results. If, however, the splanchnics be cut and the inhibitory impulses abolished, stimulation of the vagus gives constant results consisting of a slight inhibitory action followed by an increase of the rhythmical contractions of the intestine. B. _Normal Secretion Into the Intestine._