72 



that the animal substances which are most nourishing, in least bulk, of 

 easy and rapid digestion, which, by too long a stay in the intestines, 

 might become putrid, pass readily through it. In this respect, man holds 

 a middle station between those animals which feed on vegetables, and 

 those which feed on animal substances. He is, therefore, equally fitted 

 for these two kinds of food; he is neither exclusively herbivorous, nor 

 nor carnivorous, but omnivorous or polyphageus. This question, of such 

 easy solution, has long employed physicians, naturalists, and philoso- 

 phers; each bringing, in favour of his opinion, very plausible arguments, 

 drawn from the form and number of the teeth, from the length of the in- 

 testinal canal, from the force of its parietes, 8tc. 



The parietes of the digestive tube are essentially muscular; a mucous 

 membrane lines its inside, forming within it various folds ; lastly, a 

 a third coat is accidentally placed over the other two ; and is furnished 

 by the pleura to the oesophagus, by the peritoneum to the stomach, as 

 well as to the intestinal canal. 



The characteristic of this third coat is, that it does not cover the whole 

 surface of the parts of the tube to which it is applied. The muscular coat 

 may be considered as a long hollow muscle, extending from the mouth to 

 the anus, and formed throughout almost all the whole of its length, by two 

 layers of fibres, the one set longitudinal, the other circular. The will di- 

 rects the motions of the two extremities, while the rest of its course is 

 not under its controul. In the cells of the tissue which unites its surfaces 

 to the other coats, fat never accumulates, which might have impeded its- 

 contractions, and straitened and even obliterated the tube along which the 

 food was to pass*. 



III. Of food, solid and liquid. The aliments which nourish man are ob- 

 tained from vegetables, or from animals. The mineral kingdom furnishes 

 only condiments, medical substances, or poisonsj. 



By aliment is meant whatever substance affords nutrition, or whatever 

 is capable of being acted upon by the organs of digestion. Substances 

 which resist the digestive action, those which the gastric juice cannot 

 sheathe, whose asperities it cannot soften down, whose nature it catvnot 

 change, possess to a certain degree the power of disturbing the action of 

 the digestive tube, which revolts from whatever it cannot overcome: there 

 is no essential difference between a medical substance and a poison. Our 

 most active remedies are obtained from among the poisonous substances; 

 tartar emetic, corrosive sublimate, opium, all of them remedies of so 

 much efficacy in skilful hands, when administered unseasonably, or in too 



* The digestive tube comprehends, 1. the mouth ; 2. the pharynx ; 3. the oesopha- 

 gus; 4. the stomach; 5. the small intestines; 6. the large intestines; 7. the anus. The 

 commencement and termination of this apparatus are subjected, but not completely, 

 to the influence of the will. Volition and sensation are distinctly evinced in the mouth 

 and pharynx ; in the oesophagus and stomach the influence of the will gradually disap- 

 pears, and sensation becomes imperfect and peculiar. It is in consequence of the dis- 

 tribution of voluntary nerves, in greater or less number, to certain parts of the digestive 

 canal, and of the accession thus brought to the ganglial system of nerves with which it 

 is chiefly supplied, that many of the sensations and operations which belong to its upper 

 portion,'as the pharynx, oesophagus and the stomach, are so peculiar, and so difficult of 

 explanation. Copland. 



\ MACKNJUE arranges the aliments which nourish man according to the immediate 

 principle which predominates in their composition. After this manner he distinguishes 

 nine classes; namely, farinaceous, mucilaginous, saccharine, acidulated, oleaginous, 

 milky or cheesy, gelatinous, album: nous. f>Tv! lihrinous pTim.i'nts Copland, 



