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portion (fig. 221). In the outer or cortical part of the gland (fig. 223) the intervals between the trabeculæ are comparatively

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former it is arranged as follows: occupying the central and chief part of each alveolus, is a more or less wedge-shaped mass of

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Fig. 222.-Section of medullary substance of an inguinal gland of an ox; a, a, glandular substance or pulp forming rounded cords joining in a continuous net (dark in the figure); c, c, trabecule; the space, b, b, between these and the glandular substance is the lymph sinus, washed clear of corpuscles and traversed by filaments of retiform connective-tissue x 90. (Kölliker.)

adenoid tissue, densely packed with lymph corpuscles; but at the periphery surrounding the central portion and immediately next the capsule and trabeculæ, is a more open meshwork of adenoid tissue constituting the lymph sinus or channel, and containing fewer

lymph corpuscles. The central mass is enclosed in endothelium, the cells of which join by their processes, the processes of the adenoid framework of the lymph sinus. The trabeculæ are also covered with endothelium. The lining of the central mass does not prevent the passage of fluids and even of corpuscles into the lymph sinus.

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Fig. 223.-Diagrammatic section of lymphatic gland. a.., afferent; e.l. efferent lymphatics; C, cortical substance; .h., reticulating cords of medullary substance; .s., lymph-sinus; c., fibrous coat sending in trabecule; t.r., into the substance of the gland. (Sharpey.)

The framework of the adenoid tissue of the lymph sinus is nucleated, that of the central mass is non-nucleated. At the inner part of the alveolus, the wedge-shaped central mass divides into two or more smaller rounded or cord-like masses which joining with those from the other alveoli, form a much closer arrangement of the gland tissue than in the cortex; spaces (fig. 223 b), are left within those anastomosing cords, in which are found portions of the trabecular meshwork and the continuation of the lymph sinus.

The essential structure of lymphatic-gland substance resembles that which was described as existing, in a simple form in the interior of the solitary and agminated intestinal follicles.

The lymph enters the gland by several afferent vessels, which

open beneath the capsule into the lymph-channel or lymph-path; at the same time they lay aside all their coats except the endothelial lining, which is continuous with the lining of the lymph-path. The efferent vessels begin in the medullary part of the gland, and are continuous with the lymph-path here as the afferent vessels

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Fig. 224.-A small portion of medullary substance from a mesenteric gland of the ox, d, d, trabecula; a, part of a cord of glandular substances from which all but a few of the lymph-corpuscles have been washed out to show its supporting meshwork of retiform tissue and its capillary blood-vessels (which have been injected, and are dark in the figure); b. b, lymph-sinus, of which the retiform tissue is represented only at c, c. X 300. (Kölliker.)

were with the cortical portion; the endothelium of one is continuous with that of the other.

The efferent vessels leave the gland at the hilus, the more or less concave inner side of the gland, and generally either at once or very soon after join together to form a single vessel.

Blood-vessels which enter and leave the gland at the hilus are freely distributed to the trabecular tissue and to the gland-pulp.

The Lymph and Chyle.

Lymph is, under ordinary circumstances, a clear, transparent, and yellowish fluid. It is devoid of smell, is slightly alkaline, and has a saline taste. As seen with the microscope in the small transparent vessels of the tail of the tadpole, it usually contains no corpuscles or particles of any kind; and it is only in the larger trunks that any corpuscles are to be found. These corpuscles are similar to colourless blood-corpuscles. The fluid in which the corpuscles float is albuminous, and contains no fatty particles; but is liable to variations according to the general state of the blood, and to that of the organ from which the lymph is derived. As it advances towards the thoracic duct, after passing through the lymphatic glands, it becomes spontaneously coagulable and the number of corpuscles is much increased.

Chyle, found in the lacteals after a meal, is an opaque, whitish, milky fluid, neutral or slightly alkaline in reaction. Its whiteness and opacity are due to the presence of innumerable particles of oily or fatty matter, of exceedingly minute though nearly uniform size, measuring on the average about 300 of an inch. These constitute what is termed the molecular base of chyle. Their number, and consequently the opacity of the chyle, are dependent upon the quantity of fatty matter contained in the food. The fatty nature of the molecules is made manifest by their solubility in ether. Each molecule probably consists of a droplet of oil coated over with albumen, in the manner in which minute drops of oil always become covered in an albuminous solution. This is proved when water or dilute acetic acid is added to chyle, many of the molecules are lost sight of, and oil-drops appear in their place, as the investments of the molecules have been dissolved, and their oily contents have run together.

Except these molecules, the chyle taken from the villi or from lacteals near them, contains no other solid or organised bodies. The fluid in which the molecules float is albuminous, and does not spontaneously coagulate. But as the chyle passes on towards the thoracic duct, and especially whilst traversing one or more of the mesenteric glands, it is elaborated. The quantity of molecules and oily particles gradually diminishes; cells, to which the name of chyle-corpuscles is given, appear in it; and it acquires the property of coagulating spontaneously. The higher in the thoracic duct the chyle advances, the greater is the number of chyle-cor

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puscles, and the larger and firmer is the clot which forms in it when withdrawn and left at rest. Such a clot is like one of blood without the red corpuscles, having the chyle-corpuscles entangled in it, and the fatty matter forming a white creamy film on the surface of the serum. But the clot of chyle is softer and moister Like blood, also, the chyle often remains for a long time in its vessels without coagulating, but coagulates rapidly on being removed from them. The existence of the materials which, by their union form fibrin, is, therefore, certain; and their increase appears to be commensurate with that of the corpuscles.

than that of blood.

The structure of the chyle-corpuscles was described when speaking of the white corpuscles of the blood, with which they are identical. The lymph, in chemical composition, resembles diluted plasma, and from what has been said, it will appear that perfect chyle and lymph are, in essential characters, nearly similar, and scarcely differ, except in the preponderance of fatty and proteid matter in the chyle.

Chemical Composition of Lymph and Chyle (Owen Rees).

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Quantity. The quantity which would pass into a cat's blood in twenty-four hours has been estimated to be equal to about onesixth of the weight of the whole body. And, since the estimated weight of the blood in cats is to the weight of their bodies as I to 7, the quantity of lymph daily traversing the thoracic duct would appear to be about equal to the quantity of blood at any time contained in the animals. By another series of experiments, the quantity of lymph traversing the thoracic duct of a dog in twentyfour hours was found to be about equal to two-thirds of the blood in the body.

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