336 OF DIGESTION AND NUTRITIVE ABSORPTION. 



was to separate the chyme into three distinct parts, a reddish-brown sedi- 

 ment at the bottom, a whey-coloured fluid in the centre, and a creamy 

 pellicle at the top. The central portion is probably that which is absorbed as 

 chyle ; the sediment, partly consisting of the insoluble portion of the food, and 

 partly of tne biliary matter itself, is evidently excrementitious ; the creamy or 

 oily portion is probably taken up by the lacteals, and appears as fatty matter 

 in the fluid drawn from them. 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. 



447. 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 fsecal 

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

 of the enteritic mucous membrane, and of its glandulse ; the surface of the 

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

 but the glandulae, 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 glandulse, 

 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 

 often much greater than that which has been ingested, and must be derived 

 from the blood. The secretion of the caecum has bejsn ascertained to be in 

 herbivorous animals, distinctly acid during digestion ;" and there is reason to 

 believe that the food there undergoes a second process analogous to that to 

 which it has been submitted in the stomach, and fitted to extract from it what- 

 ever undissolved alimentary matter it may still contain. There is no evidence, 

 however, that this is the case in Man, whose ccecum (commonly termed the 

 appendix cosci vermiformis) is very small, compared to that of most herbivorous 

 animals. 



V. Nature of Chy unification. 



448. The causes of the reduction of the food in the Stomach have long been 

 a fruitful source of discussion amongst physiologists ; and various hypotheses 

 have been devised to account for it. Some have compared the Stomach of 

 Man to the Gizzard of a fowl, and have supposed that the trituration of the 

 food between its walls was the essential element in the process ; but this 

 doctrine is completely incompatible with the fact, that digestible substances, 

 inclosed in metallic balls with perforations in their sides, are still dissolved by 

 the power of the gastric fluid, though the walls of the stomach do not come in 

 contact with them. Others, again, have imagined that the process of digestion 

 is one of putrefaction ; but this idea, putting aside its inherent absurdity, is 

 proved to be incorrect by the fact, that the gastric juice has a decidedly anti- 

 septic quality. Others, in despair of obtaining any other solution, have attri- 

 buted the operation to the direct agency of the vital principle ; forgetting that, 

 as long as the aliment remains within the stomach and intestinal canal, it can 

 no more be the subject of any peculiarly vital process, than if it were in contact 

 with the skin, of which the mucous membrane is out an internal reflexion. 

 The theory of chemical solution, which was at first regarded by many as quite 

 untenable, has been of late years so much strengthened by new facts and 

 arguments, that there now appears no valid reason for withholding our assent 

 from it ; even though it cannot yet give a complete explanation of the complex 

 phenomena in question. The chief opposition to this theory has arisen from 

 the difficulty of imagining that any simply chemical solvent should have the 

 power of acting on so great a variety of substances, and of reducing them to 



