CHYMIFICATION. 577 



The ordinary course and direction of the revolutions of the food, 

 according to Dr. Beaumont, 1 are as follows: The bolus, as it enters 

 the cardia, turns to the left; passes the aperture; descends into the 

 splenic extremity, and follows the great curvature towards the pyloric 

 end. It then returns in the course of the lesser curvature, and makes 

 its appearance again at the aperture, in its descent into the great cur- 

 vature to perform similar revolutions. That these are the revolutions 

 of the contents of the stomach, he ascertained by identifying particular 

 portions of food; and by the fact, that when the bulb of the thermome- 

 ter was introduced during chymification, the stem invariably indicated 

 the same movements. Each revolution is completed in from one to 

 three minutes, and the motions are slower at first than when chymifi- 

 cation has made considerable progress. In addition to these move- 

 ments, the stomach is subjected to more or less succussion from the 

 neighbouring organs. At each inspiration it is pressed upon by the 

 diaphragm; and the large arterial trunks in its vicinity, as well as the 

 arteries distributed over it, subject it to constant agitation. 



It has been already remarked, that the peristaltic action of the sto- 

 mach, and the action extends likewise to the intestines, is effected 

 by the muscular coat of the organ. It is, however, an involuntary con- 

 traction, and appears to be little influenced by the nervous system ; 

 continuing, for instance, after the division of the eighth pair of nerves; 

 becoming more active, according to M. Magendie, 2 as animals are more 

 debilitated, and even at death ; and persisting after the alimentary 

 canal has been removed from the body. MM. Tiedemann and Gmelin, 3 

 however, affirm, that by irritating the plexus of the eighth pair of 

 nerves situate around the oesophagus with the point of a scalpel, or 

 touching it with alcohol, the peristole of both stomach and intestines 

 can be constantly excited ; and Valentin and Dr. John Reid state, 

 that distinct movements may be excited in the stomach by irritating 

 the pneumogastric. This involuntary function, as well as that exerted 

 by the heart and other involuntary organs, affords us a striking instance 

 of the little nervous influence, which seems to be requisite for carry- 

 ing on many of those functions that have to be executed independently 

 of volition through the whole course of existence ; and which appear to 

 be excited at times, in a reflex manner, by the presence of appropriate 

 excitants ; of food, in the case of the peristaltic action of the stomach ; 

 of blood, in that of the heart, &c. ; and yet may be carried on in the 

 absence of all nervous influence, as in the cases of the intestinal canal, 

 and the heart, which may contract for a long time after they have been 

 removed from the body. In the intestinal canal, the movements are 

 doubtless influenced by the spinal cord, probably through the sympa- 

 thetic by means of the fibres which the canal derives from it ; but 

 although influenced by the spinal cord, they are not dependent upon it 

 for contractility. As Dr. Carpenter has remarked, the canal is ena- 

 bled to propel its contents by its inherent powers ; but as in other 

 instances the nervous centres exert a general control over even the 



1 Op. citat, p. 110. a Precis Elementaire, ii. 20. 



3 Die Verdauung, u. s. w. or French edit., Recherches sur la Digestion, Paris, 1827. 



VOL. i. 37 



