OCR Text |
Show 68 Tbe Valws of the Lacteals and Lympbatz'cs. pass into the lymphatics ofthe intestines. In the porpoise, the valves of the The Valves of the Lacfcals and Lynzpbatics. 69 system in fish of cold blood, was not certain whether the lymphatics had Dr. Hunter once met with a body, where the valves were so ill adapted to the diameter of the vessels, that they allowed air to pass contrary to the course of the absorbed fluids. He inflated all the lacteals on the intestines from the thoracic duct; and, supposing that he could do this again when he pleased, neglected the opportunity of filling them with quicksilver. The same accident happened to Marchettis, according to Haller's account, who valves or not. He says, " These vessels in fish either have no valves, or mentions it tints :---" Qui, inflato chyli reeeptaculo, omnia in toto corpore the valves readily give way ; for it is an easy matter to fill them contrary to I have a preparation of the stomach of a skate, animalis pellucida vaseula aere distendit." And he ushers in this case, by the observation of " Non semper fidae custodes valvulae."--He observes in which I first injected the arteries and veins, and last of all the lymphatic also, that similar, unexpected, and uncommon retrograde motion of fluids, vessels; but I was obliged to inject them in the course of the lymph; and injected into the absorbents, had happened under his own eye. He parti- cularly mentions his having injected the absorbents of the lungs (mm c011- cnlerzata retieullmtfaciwztia) from the superior part of the thoracic duct. It has been very seldom that anything of this kind has occurred to me; and, though I do not deny that it may sometimes happen in the dead body, yet I doubt very much if ever it happens in the living. In the diabetes, it has been supposed that the chyle flows retrograde from the thoracic duct into the lymphatics of the kidney; from them into the eryptre, so into the tubttli uriniferi, thence into the infundibula pelvis, ureter, and so into the bladder. This opinion is mere supposition, depending on no experiments; lacteals are exactly as in quadrupeds, or perhaps still more numerous; so that it is not possible to inject these vessels otherwise than in the course of the chyle, that is, on the side ofthe intestines. Mr. Hewson, notwithstanding his describing particularly the lymphatic the course of the lymph." the injected vessels appeared to have valves, in the same manner as the lymphatics of other animals. For my own part, I should not easily believe any vessel to be a lymphatic, where the characteristic of valves is wanting. I had once an opinion, that the intention of the valves, in the ahsorhcnts, was not only to prevent retrograde motion in the absorbed fluids, but to intersect the column of the flttid, and prevent the pressure of the whole fluids in the vessel from affecting chiefly its lower extremity; the conse- quence of which would be dilatation and varix at that place. I am not certain that this opinion is not well founded; for the red veins of the lower extremities, which sustain the longest column of blood, are more frequently varicose than any other in the body, those of the arm being in proportion very seldom affected. Accordingly, I conceived, that if this opinion was just, the valves would be more wanted in animals who were more frequently in an erect posture, as their lymphatics would necessarily be obliged to support a greater weight of fluids than those of animals who where gene- rally in ahorizontal position; and I thought this opinion confirmed, by finding that the thoracic duct in horses has few valves, compared with the same duct in monkies, where it is quite crowded with them. But when I came to consider, that in the turtle and porpoise, who are more commonly in the horizontal posture, the lymphatics were nevertheless crowded with valves, I became less satisfied; especially as the valves must all be open when the fluid is passing forward, and therefore the pressure of the whole column must be acting at that time. Dr. and, besides that all such opinions should be rejected; why shottld the chylc flow retrograde in the lymphatics of the kidney, and not in the lac- teals themselves? and why are not the fzeces fraught with a similar fluid, as well as the urine? The arteries of the kidneys are on these occasions pra- tcrnaturally enlarged, particularly those of the cryptx, or minute glands which secrete the urine; and it is infinitely more probable, that the fluid of the diabetes arises from some remarkable change in the vessels usually se- creting the urine, than from any imaginary retrograde motion of the chyle through the lymphatics of the kidnies. |