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Show and Sensibility, of Lacteals and Lymphatics. Of tbc Coats, Irr'imbilify, Muscularity, Vasa V(130mm, nces, have but repeated examinations of the villi, under similar circumsta branches. now taught me the real structure of their orifices and primary is, by They arise out oftlie lymphatic glands exactly in'tlie same way, that form small orifices belonging to radiated branches, which presently unite to one vessel. Every ei'lort Ihave made to detect the orifices of the lympha- tics, has hitherto been ineffectual. I have looked for them on the villi of opportu- the lips, villi of the toes and fingers; but we have not there the It is also nity of finding them filled with a white fluid, as In the» intestines. in de- necessary here to wait the effect ofputrefaction, or of boiling water, taching the cuticle, which makes any after appearance ofcourse very doubt- ful. This circumstance, however, when it is considered that lacteals and lym- phaties are the same vessels, is probably of no consequence. There may be some little variety, but the orifices and beginnings we may consider, from so great analogy in other respects, as very much resembling each other. C H A P. XII. 0f tbe Coats, Irritability, Musculrzrify, Vasa Vasorum, and Sensibility, 0f Lactmls and Lymphatics. ANATOMISTS have found, that the substance of the larger arteries may readily enough be separated into three strata; to these they have given the name of coats; and speak of an external, internal, and middle coat of an artery. The substance of which the larger red veins are formed, may like- wise, though with more difficulty, be separated into coats. 61 were also fibrous, and demonstrated this in the thoracic duct of horses. I have repeatedly demonstrated these fibres in the same duct, and have now an engraving of them in my possession. I have also contrived a method of demonstrating that it has at least two coats; for I inverted a portion of the duct, and drew it on a glass cylinder; the cylinder was somewhat larger than the portion of the duct, and, as I expected, the internal coat tore, and showed the outer one entire under it. I have sometimes seen fibres in the human thoracic duct, when it happened to be uncommonly large; but more generally, even in this trunk of the absorbents, no fibres are to be seen. The muscles of the more perfect animals are all fibrous, and there- fore anatomists frequently infer muscularity in parts, from the presence of fibres; but they are by no means a certain mark of muscularity. The ten- dons, aponeiiroses, bones, cellular membrane, brain, and nerves, are all of them fibrous, but not at all muscular. On the other hand, there are many parts, such as the skin, &c. in which there is no appearance of fibres, even when viewed with our best microscopes, which are certainly capable of muscular motion. The best proof we have of muscularity in a part of a living animal, is the disposition it has to be acted upon by a stimulus, so as to be made to contract and relax every time it is applied to it. This disposition we call irritability; and the actual contracting and relaxing is muscular motion. By this test we shall be able to prove, that the lacteals and lymphatics are irritable and muscular. They not only empty themselves quickly on the admission of cold air, but, when touched in one part with oil of vitriol, or similar stimulants, contract through their whole length, as muscular fibres are known to do from such applications. Hallcr appears to have paid great attention to this subject, and convinced himself These coats fully of the fact:-" Sed etiam in vivo animale, aut nuper mortuo, non become thinner, the farther we go from the beginning of the trunks, till at last it is no longer possible to separate them in the branches, and their ex- istence is only inferred from analogy. Of the coats of arteries, two are commonly fibrous; in which respect they resemble the substance of the muscles: the internal coat has no visible fibres. Till the time of Nuck, the lymphatic vessels were conceived to have but one coat, and that similar to the internal one of arteries and veins, that is, without any visible fibres. Nuck was the first who asserted, that their coats were solus ductus thoracicus, qui vere de genere vasorum lymphaticorum est, et perinde vasa lympliatica liepatis, ad olei vitrioli tactum contraliuntur, et celerrime cxinaniuntur, scd imprimis in animale cui plena fucrunt, aut cliylo, aut lympha, aut caeruleo liquore queni animalia absorberc cocgi, sub ipsis intentis meis oculis, toties vidi liaec sive lymphatica vascula sive lactea cvanescere: non potuerunt autem visui se subduxiSse, nisi expulso qui replcbatet conspicua reddcbat liquore, lympha, lacte, indigo in aqua dissoluto." 2-: "51wa up-.. . 60 |