ABSORPTION in physiology (from ab sorbeo: Lat. absorptio, Fr. absorption, Ger. die einsaugzeng, Ital. assorbimento.) The term absorption is employed in physiology to de signate a vital organic function, the primary or immediate object of which is to furnish the system with a due supply of matter for its growth and subsistence. It is proposed, in the following article, first, to give an account of the organs by which the function is performed ; this will lead us, 2dly, to consider the question of venous absorption ; in the third place, we shall inquire into the mode in which the ab sorbents act ; and, lastly, we shall offer some remarks upon the specific uses of the different parts of the absorbent system, and upon the re lation which it bears to the other vital functions.
§. 1. Description of the Absorbent System.— We propose, in the first instance, to restrict the term absorbent system to those organs, which are supposed to be exclusively appropriated to the function of absorption ; these may be in cluded under the two heads of vessels and glands, the vessels being again subdivided into the lacteals and the lymphatics.
Although the absorbents are distributed to al most every part of the body, and perform, so im portant an office in the animal economy, they were among the organs which were the latest in being discovered by anatomists. There are, indeed, some passages in the writings of Galen,* which would lead us to suppose that certain parts of the absorbents had been seen by Erasistratus and Herophilus, as well as by himself; but it appears that they were, all of them, unacquainted with the relation which these vessels bore to the other organs, and were entirely ignorant of their office and destination. These scanty observations of the ancients seem to have been entirely neglected, or even for gotten, until the study of anatomy was revived, together with that of the other medical sciences, in the sixteenth century. In the course of the researches which were then made into the structure of the animal body, various parts of the absorbent system appear to have been brought into view, and are noticed, among other writers, by Fallopio,* who discovered the lym phatics, connected with some of the abdominal viscera, and by Eustachio,j- who detected the thoracic duct. But although their descriptions, especially that of Eustachio, are sufficiently correct to enable us to identify them, as forming a part of the absorbent vessels yet they were unacquainted with their specific nature and office, and with their relation to the sangui ferous system.
It is generally admitted that the merit of the discovery of the lacteals is due to Aselli ; this discovery he made in the year 1622. While
he was examining the abdominal viscera of a dog, he observed a series of vessels attached to the mesentery, which appeared to have no direct connexion with the arteries or veins, and which, from the circumstance of their con taining a white opake fluid, he denominated Lacteals.t He regarded them as a distinct set of vessels, exercising a specific function, distinct from that of the sanguiferous system, and he as certained that they took their origin from the surface of the intestines, and proceeded to wards the more central parts of the body, but it was not until the year 1651, that their ter mination in the thoracic duct was discovered by Pecquet. § The discovery of the other species of ab sorbent vessels, styled, from the appearance of the fluid which they contain, the lymphatics, was posterior to that of the lacteals. The trans parency of their contents rendered them less conspicuous and less easy of detection, so that, although certain parts of them appear to have been seen by Fallopio, and afterwards by Aselli and others, yet it was not until the year 1650, that they were distinctly recognized, and their connexions ascertained. The discovery of the lymphatic system was the subject of a warm controversy between Bartholin and Rud bek, on the merits of which we are, after so long an interval, scarcely able to decide. It appears, however, to have been the opinion of Haller, and the most distinguished anatomists of the last century, that the lymphatics were detected, in the first instance, by Rudbek ; that Bartholin had some intimation of the dis covery, that he then took up the subject, and pursued it much farther than it had been done by Rudbek.s There is a third individual, on whose behalf a claim of priority has been made, which pos sesses at least considerable plausibility. We are informed by Glisson, that an English ana tomist of the name of Joliffe distinctly re cognized and exhibited the lymphatics of many of the abdominal viscera, previously to the alledged discovery of either Rudbek or Bar tholin.j- But even if we allow Joliffe the full merit both of discovering these vessels, and being aware of their specific nature, it does not appear that lie published his discovery, so that it will scarcely affect the rival claims of the former anatomists. The discovery of the ab sorbent or conglobate glands, as they have been termed, was made, for the most part, at the same time with that of the vessels, as a ne cessary consequence of the intimate connexion which subsists between them.