ACTION OF THE INTESTINAL TUBE. 335 



resisted, then allowed to pass, and then grasped by the muscular parietes 

 beyond, so as to be drawn in : whence it is evident that the contraction has 

 for its object, to resist the passage of solid bodies into the pyloric extremity of 

 the stomach, at this stage of digestion, whilst the matter which has been 

 reduced to the fluid form is pumped away (as it were) by the action of that 

 portion of the viscus. These peculiar motions continue, until the stomach is 

 perfectly empty, and not a particle of food or chyme remains. Of the degree 

 in which they are dependent upon the influence of the Nervous System, some 

 idea has been already given ( 235) ; there is yet much to be learned, how- 

 ever, especially in regard to the degree in which the movements may be 

 checked or altered, by impressions transmitted through the nervous system. 

 It is stated by Brachet that, in some of his experiments upon the Par Vagum, 

 some hours after the section of the nerve on both sides, the surface only of the 

 alimentary mass was found to have undergone solution, the remainder of the 

 mass remaining in the condition in which it was first ingested ; and if this 

 statement can be relied on, it would appear that the movements of the stomach, 

 like those of the heart, can be readily affected by a strong nervous impression. 

 It may be partly in this manner, therefore, and not by acting upon the secre- 

 tions alone, that strong Emotions influence the process, as they are well 

 known to do. On the other hand, the moderate excitement of pleasurable 

 emotions may be favourable to the operation, not only by giving firmness and 

 regularity to the action of the heart, and thence promoting the circulation of 

 the blood, and the increase of the gastric secretion, but also in imparting firm- 

 ness and regularity to the muscular contractions of the stomach. 



IV. Action of the Intestinal Tube. 



446. The pulpy substance to which the aliment is reduced, by the me- 

 chanical reduction and chemical solution it has undergone in the mouth and 

 stomach, is termed chyme. The consistency of this will of course vary in 

 some degree with the quantity of fluid ingested; in general it is grayish, 

 semifluid, and homogeneous ; and possesses a slightly acid taste, but is other- 

 wise insipid. Dr. Beaumont describes it as varying in its aspect, from that 

 of cream, which it presents when the food has been of a rich character, to 

 that of gruel, which it possesses when the diet has been farinaceous. The 

 passage of the chyme through the pyloric orifice is at first slow ; but when 

 the digestive process is nearly completed, it is transmitted in much larger 

 quantities. From the time that the ingested matter enters the intestinal 

 canal, it is propelled by the simple peristaltic action of its muscular coat, which 

 is directly excited by the contact either of this matter, or of the secretions 

 which are mingled with it ;* and all that is not absorbed is thus conducted to 

 the rectum, its expulsion from which is due to an action of a distinctly reflex 

 kind, excited through the nervous centres ( 202). During its progress 

 through the intestinal tube, the product of the gastric operation undergoes 

 very important changes. The chyme is mingled in the duodenum with the 

 biliary and pancreatic secretions, which effect an immediate alteration both in 

 its sensible and chemical properties. The nature of this alteration can be best 

 estimated, by mingling bile with chyme removed from the body. This has 

 been done by several experimenters on the lower animals ; and by Dr. Beau- 

 mont in the case already referred to, which afforded him the means of obtaining 

 not only chyme, but bile and pancreatic fluid. The effect of this admixture 



* The bile seems to have an important share in producing this effect; since, when the 

 ductus choledochus is tied, constipation always occurs. The action of mercury as a 

 purgative appears to take place through the increase of the hepatic and other secretions 

 which it induces. 



