Galactophoriductus, (from milk, and to carry). The lacteal vessels.

These vessels were not unknown to Erasistatus and Herophilus, and are distinctly mentioned by Galen. It was supposed, very early, that they conveyed the nutriment from the intestines; but, as usually the liver was considered to be the part in which the blood was elaborated, these vessels were said to terminate in that organ. Plates still exist in which they are represented as taking this course, though it had been contradicted by Galen. To Asellius the credit of the discovery has been given, and the exact day fixed, viz. the 23d of June, 1622, when opening a dog for an experiment of a very different nature: but, in reality, he saw them only as Galen and his predecessors had done; and so far from tracing their course to the thoracic duct, he described them as terminating in the liver. He saw, however, their valves, and conjectured, rather than demonstrated, that they receive their contents by orifices opening into the intestines. It is singular that he had not connected with this discovery the description of the thoracic duct by Eustachius, in 1563, which would at once have cleared up the principal circumstances of this lesser course of the lymph or chyle.

Asellius never saw the lacteals in the human body, but supposed their existence from analogy; and it was twelve years afterwards, viz. in 1634, that Veslingius first discovered them, and added, in the year 1649, the revival of the discovery of Eustachius, viz. the existence of the common receptacle of the lacteals and lymphatics, the thoracic duct. Rudbeck, nearly at the same era, without any previous communication, discovered the lymphatics in quadrupeds; and about the year 1654 traced the duct in the human body. About the same time our countryman, Dr. Jolyfe, also discovered the lacteals and lymphatics without any knowledge of Rud-beck's success. As these authors discovered them in man and in quadrupeds, so Bartholine seems first to have seen them in fish.

Thus the existence of an absorbing system was apparently ascertained; and, since that period, gradual additions were made to its exten t; but the great questions remained undecided: was the absorbent system of vessels general in every part of the body; and were these newly discovered vessels the only ones destined for this purpose ? The answer to the first question would, in part, decide the second; for were they general, they were propbably the only absorbents. As the extent of their range was increased, therefore the opinion of their being exclusively absorbents was stronger; but, in 1757, Dr. Monro published, at Berlin, a short dissertation, by which he endeavoured to prove, by a few simple and decisive experiments, that the lymphatics were a general system of absorbents. The honour of the discovery was soon after claimed by Dr. Hunter, and a controversy of some asperity was for a time carried on. The observations which we offered on the discovery of the circulation will apply precisely to the present dispute; nor was it without design that we have called the system of the lacteals the"lesser course," comparing it to the lesser circulation through the lungs. In fact, the former discoveries had placed this so much on a level with even a common capacity, that it required not the reach of a giant to grasp it. Dr. Monro had undoubtedly the honour of first bringing it forward in a compact scientific form.

At that time, however, and long since, the question was not decided, whether the lymphatics were exclusively absorbents. It is admitted that red veins do perform this office, in the fcetal part of the placenta, for instance, and in the corpora cavernosa penis. We cannot, therefore, deny their powers; and as the lymphatic system seems not to be equally extensive in every part, it is still possible that the veins may supply their place. We consequently have left the question apparently at issue in the articles Absorbentia vasa and Absorptio; but have little hesitation in offering our opinion, that the lymphatics, except in parts of a peculiar construction., are exclusively absorbents.

We have thus spoken of the lymphatics and lacteals as the same. In fact, they are the same in structure, in direction, and office. The lymphatics sometimes carry a milky fluid, and the lacteals a serous one; each conveys occasionally blood, dissolved or suspended osseous matter; in short, every thing which nature requires to be removed from the cellular or other cavities of the body.

The lacteals arise from the cavity of the intestines, from beginnings almost imperceptible. The discriminating eye of Lieberkiuhn, assisted by good glasses, perceived, on examining the villous coat, vesicles like a small egg, which he styled a mpullula. These, he thought, were either the extremities of lacteals, or, at least, the receptacles of the chyle immediately absorbed. Later authors have denied the existence of these vesicles, and thought that the small ovoid receptacles were only convoluted arteries and veins surrounding the nascent lymphatic. From a careful comparison of the descriptions, we think it highly probable that Lieberkuhn was deceived, and that these ovoid vesicles are really convoluted vessels. We know that the reputed acini of many glands have been found to be vascular. If also the chyle be absorbed by capillary attraction, we know that the vessel must be very minute, or the cohesion of the fluid very inconsiderable. The chyle is, however, a milky fluid, and most probably, like all such, its molecules possess a greater attraction to each other than those of water. A vesicle, therefore, is not well adapted for absorption, and would rather impede than assist the progress of the chyle, thus opposing a function of importance, which often requires a rapid exertion. It seems more probable that the orifices of the lacteals open into the intestines, and that their mouths are very numerous, actually constituting the villi, from which the internal coat has its name, and that each villus has its artery, vein and nerve. In the usual state the villi are apparently pendulous; but when the minute arteries are excited to action, that they are erected like the fimbriae of the Fallopian tubes; and that in this way their apetures are contracted, so as to become of a proper diameter to absorb the chyle by capillary attraction.

We must not, however, conclude that anatomists of eminence and character, who have described these am-pullulse, were wholly mistaken. They have been seen by Lieberkhun, by Sheldon, and by Cruickshanks; but as it is impossible to inject them, it is doubtful whether the chyle may not impart a white colour to the mass of convoluted arteries; and we rather suspect this may be the case, since, in the moment of the discovery, it seems to have been doubtful whether the supposed orifices were not rather the interstices between the adjoining vesicles. If they were the orifices, our objection lies with additional force, that such vesicles are not adapted for capillary attraction. If, too, these were the beginning of the lacteals, they should be scattered in much greater profusion than they are represented.

When the lacteals arise from the cavity, they run along the intestines in a longitudinal direction, freely anastomosing with each other; but the course of the contents of these vessels is opposite to that of the blood. This longitudinal direction is continued for some way, and the lacteal then turns towards the mesentery, at an angle more or less acute. This lengthened course is probably designed for some peculiar purpose, probably for the animalization of this newly introduced aliment. The vessel then proceeds to the glands interposed, in which they are lost, and from which similar vessels of larger size, but less numerous, emerge. These are styled glands of the first order, as in their course to the thoracic duct other glands are found. In the whole of their progress, numerous valves are interposed to prevent regurgitation; so that sometimes a lacteal, injected with quicksilver, resembles rather a siring of silver beads than a continuous vessel.

In the course of the lacteals to the first order of glands, there are few anastomoses; but before entering the glands they are minutely divided. It sometimes happens also, that a lacteal, when it arrives at a gland, will creep over it without being immersed in it; and, at others, a trunk will pass at a little distance. The former fact we do not remember being noticed in any author; but we have often seen it in injected lacteals. Both circumstances are important, as they show how the body may be occasionally nourished when all the glands are apparendy obstructed. This also appears the object of nature, in offering different orders of glands, since it is equally necessary that the body should be nourished, and the new fluid elaborated, so that the vessel which escapes the first order may be immersed in some gland of the second, and one that has passed through the first, may escape the second. The lacteals, however, which come off at the upper portion of the canal, pass through fewer glands than those from the ileon; and in old age many of the glands are obliterated. In the duodenum, perhaps, the more perfect chyle is separated; and in old persons the fluids are so highly ani-malized, that less precaution is necessary in preparing the new aliment. In the colon, the caecum, and rectum, no lacteals have been discovered; though from the numerous lymphatic glands in the mesocolon lacteals must be found there. From the glands the lacteals pass on to the thoracic duct, and probably, in their course, anastomose with some of the lymphatics.

For the structure of the lacteals, see Lymphae ductus, and for the glands, Lymphatic glands. See also Ductus thoracicus; Monro de Venis Lym-phaticis Valvulosis; Meckel de Finibus Venarum, See.; Monro's Three Treatises, and his Observations Anatomical and Physiological; Hewson's Experimental Inquiries, part ii.; Sheldon on the Absorbent System; Cruickshanks' Anatomy of the Absorbent System; Mascagni Vasorum Lymphaticorum Corporis Humani Historia.

The chylifera vasa are also called vene lacte because their valves are disposed as those of the veins are, and because, like them, they convey their contents from smaller to larger tubes.

Dr. Harvey discovered the lymphatics in the year 1616. In 1627, they were published by another author. Uzzalius discovered the lacteals in a dog, running to the mesenteric glands, in the year 1662. See Winslow's Anatomy.