ACTION OF THE INTESTINAL TUBE. 501 



vourable 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 firmness and regularity 

 to the muscular contractions of the stomach. 



660. Action of the Intestinal Tube. The pulpy substance to which the 

 aliment is reduced, by the mechanical reduction and chemical solution it has 

 undergone in the mouth and stomach, is termed chyme. The consistence of 

 this will of course vary in some degree with the quantity of fluid ingested ; 

 in general it is greyish, semifluid, and homogeneous ; and possesses a slightly 

 acid taste, but is otherwise 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 ( 391). 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 eft'ec't an immediate altera- 

 tion both in its sensible and chemical properties. The nature of this altera- 

 tion 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. Beaumont 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 was to separate the chyme into three distinct parts, a red- 

 dish brown sediment at the bottom, a whey-coloured fluid in the centre, 

 and a creamy pellicle at the top. The central portion, with the creamy pelli- 

 cle, seems to constitute the chyle absorbed by the lacteals ; the creamy matter 

 being chiefly composed of oily particles; and the wheyey fluid having pro- 

 teine-compounds, saccharine and saline matters, in solution : the sediment, 

 partly consisting of the insoluble portion of the food, and partly of the biliary 

 matter itself, is evidently excrementitious. It is not until the food has passed 

 the orifice of the Ductus Choledochus, that the absorption of chyle begins, 

 the lacteals not being distributed upon the Stomach, or the higher part of the 

 Duodenum. 



661. By the gradual withdrawal of their fluid portion, the contents of the 

 alimentary canal are converted into a mass of greater consistence ; and this, 

 as it advances through the small intestines, assumes more and more of a faecal 

 character. A part of the faeces, however, may be derived from the secretions 

 of the enteritic mucous membrane, and of its glandules ; the surface of the for- 

 mer, with its simple follicles, probably secretes nothing else than mucus ; but 

 the glandidx, with which it is so thickly studded, appear to serve as the 

 channel for the elimination of putrescent matter from the blood. There can 

 be no doubt, that a large quantity of fluid is poured out by these glandulae, 

 when they are in a state of irritation from disease, or from the stimulus of a 

 purgative medicine ; since the amount of water discharged from the bowels is 



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

 (1 net us 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 in- 

 duces. 



