LYMPHATIC AND LACTEAL SYS TEM.—(Fr. Systime lymphatique ; Germ. Saugadersystem oder .Lymphgefusssystem.
Syn. Absorbent systcm.)—The lymphatic sys tem is composed, in the first place, of the vessels which collect and convey the lymph from all parts of the body and the chyle from the intestines, and ultimately deposit them in the veins. Secondly, of the small fleshy bo dies called conglobate, lymphatic, or absorbent glands, which are found connected with this system of vessels in various parts of their course.
The lymphatic system is confined to the class Vertebrata. It is the least complicated in Fishes, and consists in them simply of pel lucid valveless vessels. In Reptiles, also, it is composed of these vessels only, but which are armed with more or less perfect valves. In the two higher orders of Vertebrata, Birds and Alammalia, to the vessels containing very nu merous and perfect valves, the conglobate glands are superadded : in all, however, the ter mination of the system is in the veins, and its origin and general arrangements are probably in all essentially the same.
The different parts of the lymphatic system had escaped the notice of anatomists until the middle of the sixteenth century, and the entire system was not discovered till the middle of the seventeenth. I must here except the lym phatic glands, which from their large size must have been observed by the earliest anatomists, and we accordingly find them alluded to by IIippocrates, who classed them with the other glandular organs.
The first isolated discovery in the vascular part of this system was made by Eustachius in 1563, who saw and described accurately the thoracic duct in a horse. lie called it the vertu alba thoracis, and traced it downwards from the left subclavian vein to the lumbar ver tebrae, where he noticed the dilatation now called the receptaculum chyli ; he however had no conception that it formed the trunk of a se parate system of vessels, but conceived it to be a vein of a peculiar kind. Fifty-nine years af terwards, in the year 1622, Asellius was fortu nate enough to discover the lacteal vessels on the mesentery of a dog; and although on the following day he was much disappointed in not being able to see them in another dog in spected for the purpose, by continuing his re searches lie soon convinced himself of their ex istence in most animals. Ile also attributed to
them their proper function, having remarked that whenever there was chyle in the intestines, these vessels also contained a white fluid, and could then only be seen. Ile failed, however,to connect the vena alba thoracis, the discovery of Eustachius, which had probably been for gotten, with his own, and mistaking the lym phatics of the under surface of the liver for the continuation of his vessels, was led into the error of supposing them to terminate in the liver. Asellius, who died in 1626, had not seen the lacteals in man, but inferred and as serted their existence. According to IIaller, Veslingius was the first who saw these vessels in the human subject, in the year 1639 ; but Breschet informs us, in his Systome Lympha tique, page 4, that, "en 1628, les lympha tiques du m6sentbre furentapercus pour la pre mibre foil chez l'homme. l'eiresc, Senateur d'Aix, informe par Gassendi de la &convene qu' avait faite Aselli, distribua plusieurs exem plaires de l'ouvrage de ce proflesseur aux me decins de sa connoissance, et leur abandonna un criminel condamne it mon, pour verifier le fait sur son cadavre. On fit hien manger cet homme avant de le conduire au supplice, et une heure et dernie aprs sa mort, I ouverture du bas ventre montra le mesentt•re tout con vert de vaisseaux lactes pleins de chyle." The thoracic duct was rediscovered in the year 1649, by Pecquet, who published a de scription of it in 1651. Haller ascribes this discovery to Veslingius : " Mein Veslingius, nisi pluranum fallor, primus post Eustachium, contra cannes comtaneos, rectius anno 1649, vide vas lacteum grande, in pectus adscendere ; cum reliqui incisores, partim ab Asellio per suasi, et partim a lymphaticis vasis hepatis se ducti, chyliferos ductus ad hepar ducerent." It now became evident that the thoracic duct was the trunk of the vasa lactea, and that the chyle was not conveyed to the liver, as Asellius supposed, but was poured into the venous sys tem at the union of the subclavian and internal jugular veins of the left side. The lymphatics of the under surface of the liver were soon after sliewn by Glisson and Veslingius to have their valves so arranged as to convey their contents from, and not to this organ.