It will be at once perceived, that the discovery of Asellius was imperfect : He only supposed that these vessels went to the liver ; to trace them to the fountain of the blood was an honour reserved for Pecquet, French anatomist, who, about thirty years atter, on open Mg the heart of another live dog, saw a whitish fluid mingling with the blood, and flowing in with a constant stream. Examining the source of this fluid, he was led to discover the large trunk in which all the vessels seen by Asellius terminate. With a modesty equal to that of Asellius, he cautions his readers to ascribe Lois discove ry to no superior acuteness or diligence on his part, nor to accuse preceding anatomists of neglect or inac curacy ; candidly acknowledging that his merit was com paratively small, and that his discovery was to be at tributed entirely to chance, or the kindness of Provi dence. It cannot be supposed, that a man so modest and unassuming, would, had lie known it, have studiously concealed the discovery of Eustachius, who had long be fore described the same vessels in a horse, though he knew neither its origin nor its use : the discovery of which constitutes the high merit of Pecquet.
With these discoveries of Asc llius and Pecquet,anato mists would probably have remained satisfied, and would never have thought of looking for any more ves sels to explain the functions of the animal system, had not Olans Rudbeck, a Swede, and afterwards Thomas Bartholine, a Dane, on opening the bodies of live dogs, accidentally discovered a number of similar vessels, arising front various parts of the body, and ending, along with the lacteals of Asellius, in the trunk discovered by Pecquet. These vessels were afterwards found in sheep, in goats, and in man : Bartholine saw them on the liver of a fish, and Dr Monro and Mr liewson have since demonstrated them in a variety of fishes and birds. In short, they form a part of the animal system, and have been found in every part of the human body by va rious anatomists, and in the brain by the celebrated Mas cagm. From an opinion that they were branches of the same system with the lacteals of Asellius, they were named by Bartholine vase lactea ; and, from the nature cc the fluid which they contain, easa serosa, va,w !yin and challis aqnosi.
The difficulty of making these discoveries, the great importance of which is universally acknowledged, can only be conceived by those wino are somewhat ac quainted with the subject. The lymphatics and lacte;.la can scarcely be seen even when the eye is assisted by the microscope, unless they are full ; and they seldom contain any fluid at all, except during the life of the animal, and a short time after death. We cannot much wonder, therefore, that for so many ages they escaped observation, or that, when the lymphatics were discover ed physiologists found it difficult to explain their use. The use of the lacteals of Asellius was, indeed, abundant ly obvious; but what nourishment could be conveyed by vessels arising from the very points of the extremi ties ? Among many various opinions, it was thought by Rudbeck and Bartholine themselves, that the lymphatics were designed to convey back to the heart, by suction, or absorption, all the fluids that had wandered from the course of circulation, and remained after nourishing the parts. In this persuasion Rudbeck asserts, that they
prevent accumulation of water in the cavities, and that dropsies are occasioned by their rupture or obstruction. Nor was the opinion, that such an absorption is regularly taking place in all parts of the animal body, any new idea in anatomy. It was the p-eneral and well-known doctrine of the ancients, as Kan Boerhaave plainly proves in his work, emitled, Per.vpr•atv, ditto Iklip'fcruti. The office of absorption, hoy.evcr, was ascribed to veins ; but, as it was obvious that the vessels discovered by Asellius performed the functions formerly ascribed to the veins of the intestines, Rudbeek and Bartholinc claimed the same privilege for the lymphatics in all the other parts of the body ; Vienssunius, a professor at Montpe lier, endeavoured to prove, flunk mercurial frictions, and the eflixts of bathing in water, that the same vessels opened on the surface. Similar ideas of their nature and functions had occurred to Glisson, to Willis, to Hoffman, and Mr Noguez, a french anatomist, who, as Lally as the year l7'2.7, calls them conduits absorbents, or absorbing vessels. The same doctrine has been con firmed by t \so very distinguished anatomists, the late Dr Hunter, and the present Dr llonro of Edinburgh ; ho have warmly disputed about the honour of suggest ing a thought w hick was familiar to anatomists before they were in existence.
As the of absorbents is the last great and leading discovery nettle in anatomy by means of dis section, we shall now, according to our proposed plan, take a view of the principal improvements that have been introduced in the way of demonstration. The in sufficiency of verbal descriptions had suggested to sur geons and anatomists, at a very early period, the idea of supplying this defect by pictures and figures. The ho nour of first introducing this mode of demonstration has been assigned to Leonardo da Vinci, an Italian, eminent for his knowledge of philosophy, painting, and anatomy, who died in the beginning of the 16th century ; but to this honour, whatever may his merit in other respects, he is by no means entitled. Surgical figures had been exhibited by Moschion in the third century ; and Guy de Chauliac, who flourished in the 14th century, informs us, that Hermondaville, who lived before him, had taught anatomy from figures at Montpelier. At all events, it is plain from the expression of Guy de Chauli ac, that anatomical figures were used in his time ; and Montagnana, who flourished about the middle of the 15th century, is the author of some excellent figures. So general was the practice about the beginning of the 16th century, that almost every book on anatomy was ac companied with engravings : of these we may mention the works of Peiligh, I-hind, Carpi, Dryander, Vesalius Vasseus, and Stephans.