VOL. XXXVIII.] PHILOSOPHICAL TRANSACTIONS. 579 



\ug. and that the extremity of the medullary substance, either by nature, or 

 bv some accident, laid bare, is the onlv immediate instrument of sensation. 



This being premised, the structure of the intestines, the parts in question in 

 the case before us, comes to be considered. 



The intestines are made up of 4 tunics, or coats. The first, or external 

 coat, is a common membranous covering, borrowed of the peritoneum. The 

 second is composed of their annular, contractile, muscular fibres, the imme- 

 diate instruments of their peristaltic motion. The third is the nervous coat, a 

 reticular plexus of nerves, intermixed with blood-vessels and glands, placed 

 immediately under the muscular, and over the villous coat. The fourth is the 

 villous or innermost coat, on the concave side, rightly called villous, as it 

 appears viewed through a microscope; though from its appearance to the naked 

 eye, it be erroneously called the mucous coat. This is generally allowed to 

 consist of the capillary extremities, or rather roots of the lacteals, and the 

 excretory ducts of the glands, which together form these villi that are seen in 

 it. Among these, suitable to analogy in all other parts of the body, the pa- 

 pillae pyramidales, or extremities of the nerves, are lodged uiuler the cuticula 

 of the nervous coat, for the uses of sensation, so necessary for the purposes of 

 nature, in this very sensible part, the inside of the guts, which is known to 

 be so quickly and necessarily affected by the qualities of their contents. 



The proper nerves of the first or outer coat, are those of the peritoneum, 

 of which it is a part, arising from the medulla spinalis of the loins and os 

 sacrum. Whereas the nerves proper to the guts, are of the par vagum, and 

 mensenteric plexus; therefore, as there is no communication of nerves between 

 this external coat or covering, and the proper substance of the intestines them- 

 selves, a stimulus acting on this external coat only, would not afTect the guts, 

 so as to excite in them any considerable degree, either of sensation or motion. 



Again, the proper nerves of the intestines, whose origin, disposition, and 

 situation have been already described, terminate either in the muscular con- 

 tractile fibres of the coat immediately above them, or carry their extremities 

 to the inside, where they terminate under the cuticula, for the use of sensation ; 

 so that a stimulus on the outside of the intestines, besides the difficulty of 

 passing through the two external coats, before it could reach the proper nerves 

 of the guts, would at last only irritate their sides, where they are insensible, 

 because covered with the dura mater: and if it might be supposed, that such a 

 stimulus as is in question, viz. the gall, could have penetrated through these 

 coats into the cavity, where the sensible extremities of the proper nerves of the 

 guts lie exposed to it, yet such a filtration through all these coats, as it could 

 not be performed soon, nor in great quantity, so it would enter at last, divested 

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