54 



There exists in the stomach an union of the cerebral and sympathetic 

 nerves, which explains the manifest dependency, in which that one of the 

 three supports of life is found with the brain; a dependency so marked, 

 that every strong affection of the soul, every violent agitation of the mind, 

 weakens or even totally suspends the action of digestion in the stomach. 

 This combination of cerebral and sympathetic nerves likewise accounts 

 for a phenomenon, which was mentioned in speaking of the influence of 

 habit on the action of the organs. The stomach differs essentially from 

 the intestinal canal j for, far from getting accustomed to the impression 

 of emetics, so as to become by degrees less sensible to their action, as the 

 intestines to the action of purgatives, though three grains of tartar emetic 

 could, at first, scarcely excite it, half a grain only of that salt is able to 

 bring on vomiting, when by frequent use, it has acquired the habit of the 

 motions excited by its action. It is riot in that case with the stomach, as 

 with a limb, whose muscles perform motions with the greater ease and 

 facility, when they have been often practised. 



XI. OF THE RELATIONS OF PHYSIOLOGY TO SEVERAL 

 OTHER SCIENCES. 



It would be entertaining a very incorrect notion of the science of liv- 

 ing man, to imagine with some authors, that it solely consists in the ap- 

 plication of the laws of Natural Philosophy, to the explanation of the 

 phenomena of the animal ceconomy. Physiology is an independent sci- 

 ence; resting upon truths of its own, which it draws from the observa- 

 tion of those actions, which, in their aggregate succession and connexion, 

 constitute life. It is enriched, it is true, with facts furnished to it by 

 Natural Philosophy, Chemistry, and Mathematics ; but what it has bor- 

 rowed from these, is accessory merely, and does not form an essential part 

 of the edifice of the science. Thus, the better to understand the mechan- 

 ism of hearing and vision, physiology borrows from acoustics and optics, 

 elementary notions on sound and light; and, in order to obtain a more 

 correct knowledge of the nature of our solids and fluids, and of the 

 manner in which animal substances are constantly passing from the one 

 to the other of these two conditions, physiology calls in the aid of che- 

 mistry. Thus, geometry and mechanism furnish it with the means of 

 better understanding the advantageous form of the organs, and the per- 

 fection of their structure*. 



remaining nerves are called irregular. They have a single fasciculus or root, from 

 one column of the spinal marrow. They derive their name from the irregularity 

 of their ramifications, and their want of symmetry ; are superadded to the original class 

 and correspond to the number and complication of the superadded organs. The 3d, 

 4th and 6th, going to the eye ; the 7th (portio duru) to the face ; the 9th to the tongue ; 

 the glossopharyngeal to the pharynx ; the vagus to the larynx, lungs, heart and sto- 

 mach ; the phrenic to the diaphragm ; the spinal accessory to the muscles of the shoul- 

 der ; and the external respiratory to the outside of the chest, are the irregular or super- 

 added nerves. (See Transactions of the Royal Society for 1821 ; British Journal of Sci- 

 ence, Jan. 1822 ; the first number of Magendie's Journal of Physiology ; and the Phila- 

 delphia Journal of Med. and Pliysl. Science for August, 1893, p. 240.) Godroan. 



* A knowledge of mathematics, and of the whole circle of natural philosophy, in- 

 cluding more especially chemistry and natural history, and, in a more particular manner, 

 human and comparative anatomy, is requisite to the successful study of physiology. 

 This branch of knowledge, although independent of some of these, is yet more easily 

 acquired, and its difficulties are better explained, by a previous acquaintance with all of 



