This convoluted tube forming the gland is not always cyl:nd rim!, but is occasionally dilated, and looks flattened near the surface where pressed by the capsule ; the size of this tube is much larger than that of the branches of the vasa afferentia and efferentia, a fact that has been too much overlooked by anatomists, and which leads me to conjecture that these vessels enter and arise from its convolutions by open mouths ; be this as it may, we know that the injection conveyed into the gland by the vasa afferentia readily passes from it by the vasa efferentia. I should not here omit to mention a circumstance already adverted to of consi derable interest, viz. that the injection conveyed to a gland by an afferent vessel is occasionally received by the veins of that gland, and to all appearance without rupture or extravasation. The occurrence itself is admitted by all; but physiologists differ much in their explanations of the channel by which the injection has en tered the vein. Some explain it by an extrava sation into the cellular tissue from an injury by which both sets of vessels have been opened; others, who conceive that a minute net-work of lymphatics exists on the interior of the veins and arteries, will have no difficulty in ima gining a rupture of this network; the vasa vasorum of the lyinphatics, which may be dis tinctly seen on their interior after a minute in jection, may be supposed to have given way and to have admitted the injection from the interior of the lymphatics. But these opinions will not explain .why this communication should take place within the gland only, and invariably with the vein, never with the artery. The general opinion is that this communi cation takes place accidentally, and not by any real continuity of canal. Fohmann stands almost alone in asserting that a natural commu nication does exist between the lymphatics and veins within the glands, especially in those situations where in birds, reptiles, and fishes, the lymphatics have been proved to terminate directly in the veins. Fohmann even ventures an opinion as to the mode in which the lym phatic joins the vein ; not, he conceives, by con tinuity of peripheral branches, but by an effer ent lymphatic opening into the side of a vein before the latter emerges from the gland. Without committing myself to the exact mode of union, I must confess I agree with Fohmann that a natural communication does exist in some of the glands between the lymphatics and the veins. It has been observed hundreds of times. It has occurred to every anatomist who has engaged himself with the injection of these vessels; I have met with at least twenty such instances myself, while a similar communica tion between a lymphatic and artery within a gland has never been observed. I am entirely at a loss, therefore, to account for these occur rences without admitting a natural channel to exist between the one set of vessels and the other.
I have before observed that the exact arrange ment of the bloodvessels in the interior of the canals of which the glands are constituted, is not known ; but we are equally in the dark with respect to the vascular supply received by other minute tubes, such as the seminiferous, urini ferous, and lactiferous tubes, from the capilla ries of whose lining membranes, however, we admit that their appropriate secretions are de rived. As far, then, as organisation is con cerned, there is nothing to forbid our ascribing a secreting function to the interior of the canals of the lymphatic glands, or of tre•lym phatic vessels generally. There can be little doubt but that the lymph and chyle undergo modifications in their passage through the ab sorbent glands, although we are not at present prepared to state the nature of that modification.
It has been observed that the chyle included between two ligatures in its own vessel before it has reached a gland will not coagulate, although after it has passed the gland coagula tion readily takes place. Miiller remarks from this circumstance that the glands of the mesentery appear to have the power of changing part of the albumen of the chyle into fibrin. At any rate we are warranted, from the little we do know of the structure of the absorbent gland, in asserting, that the chyle and lymph collected from various sources must be mingled together in the glands, that they must be divided into extremely minute streams on their entrance into or exit from a gland, that they must be submitted to a great extent of surfitce of their containing vessels, and subjected to considera ble delay in their passage through the gland. Mr. Gulliver's observations on the fluid con tained in the absorbent glands would almost lead us to conclude that their proper office was to fabricate the peculiar globule of the lymph and chyle ; my own observations on these fluids before and after reaching the glands would not bear out this opinion ; but as I have next to consider the characters, physical, microsco pical, and chemical, of these fluids, I shall shortly enter more fully into this subject.
Lymph is a transparent fluid, slightly opa line, of a light straw colour; its specific gravity is 1022.28, water being 1000-00; its odour, which is slight, varies, and is peculiar to each animal; is alkaline, and has a saline taste. I collected in an ounce-phial about three drachms of lymph from a large lymphatic in the axilla of a horse, by inserting a small silver tube into it. In about ten minutes the whole had coa gulated into a jelly-like mass; in half an hour a separation had taken place into a fluid and solid part : the latter formed a soft tremulous clot modelled to the form of the phial. A drop of this lymph placed on a piece of glass, and covered by talc, was submitted to inspec tion under the microscope, immediately after its removal from the vessel. A number of colourless spherical globules were observed in it having a granular surface, and precisely resembling those described by Mr. Gulliver as belonging to the mesenteric, lymphatic, and thymus glands. I am not aware whether Mr. Gulliver considers these globules as belonging exclusively to the glands, or whether he thinks them distinct from or identical with the lymph and chyle globule. My own observations lead me to state that they are found in the lymph or chyle before and after passing the glands, as well as in their transit through them. I am also dis posed to assert that these globules remain co lourless, and that whenever the lymph possesses a slightly red tint, it obtains that tint from the presence of blood corpuscules which have ac cidentally entered it. After coagulation had taken place, the lymph was again examined under the microscope, the globules were all found entangled in the clot ; scarcely one re mained in the transparent fluid. The clot, when disturbed, torn, and pressed, contracted to less than one-twentieth of its original bulk, and the few blood corpuscules it contained, being now approximated closely together in the contracted clot, gave it a slightly red tint. On examining the serum of this lymph under the micro scope a week afterwards, when putrefaction had commenced, numerous exceedingly minute animalcules were seen diffused through it in active motion.