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arteries enter. The essential part of the gland is therefore the periphery, the often kidney-like cortical substance.

In this can be distinguished, whenever the gland is at all well developed (and in some cases* of pathological enlargement it is extremely distinct) even'with the naked

eye, little, roundish, white or grey granules lying side by side. When the part is moderately well filled with blood, around each granule may be pretty nearly always discerned a red circle of vessels. These granules have long been called follicles, but it was doubtful whether they were distinct formations or mere convolutions of the lymphatic vessel protruding on the surface. Upon more delicate microscopical examination, the proper (glandular) substance of the follicles can easily be distinguished from the fibrous meshwork (stroma) which bounds them on all sides, and is externally continuous with the connective tissue of the capsule. The internal substance is chiefly composed of little cellular elements, which lie pretty loosely, being merely enclosed in a fine network of star-shaped, often nucleated trabeculae. If we attempt to search for the lymphatic vessels in the cortical substance, but very little can be discovered of them in the stroma,

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Fig. 61. Sections through the cortical substance of human mesenteric glands. A. View of the whole cortical substance slightly magnified: P, investing adipose tissue and capsule, through which blood-vessels r, v, v enter. F, F, F. Follicles of the gland, into which the blood-vessels in part plunge, at i, i the interstitial tissue separating the follicles (stroma).

B. More highly magnified (280 times). C. The tissue of the capsule with parallel fibrils. a, a. The reticulum, partly empty, partly filled with the nucleated contents. The whole corresponds to the outer part of a follicle.

STRUCTURE OF LYMPHATIC GLANDS. 175

and if a gland be injected, the injection penetrates right into the middle of the follicles. If a mesenteric gland be examined during chylification, that is perhaps three or four hours after a meal at which fat has been taken in abundance, its whole substance appears white and perfectly milky, and on examining individual parts of it microscopically, the minute fat-drops of the chyle may be detected every where lying between the cellular elements of the follicles. It seems, therefore, that the current of lymph forces its way between these elements, and that no really free channel for it exists, seeing that the elements lie crowded together like the particles in a charcoal filter, so that the lymph trickles out again on the other side in a more or less purified state. The follicles should accordingly be regarded as spaces filled with cellular elements but variously intersected by a trabecular network, and thus they can no longer be held to be convolutions or dilatations of the lymphatics, but must be viewed as interposing themselves in the course of these vessels after they have broken up into a series of ramifications continually increasing in minuteness.

Of the minute elements contained in the follicles, the cells of the parenchyma, some appears to become separated

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Fig. 62. Lymph-corpuscles from the interior of the follicles of a lymphatic gland. A. As usually seen; a, free nuclei, with and without nucleoli, simple and divided. b. Cells with smaller and larger nuclei, which are closely invested by the cell-wall. B. Enlarged cells from a hyperplastic bronchial gland in a case of variolous pneumonia (comp. in Fig. 57 the colourless blood-corpuscles from the same source), a. Largish cells with granules, and single nuclei. b. Club-shaped cells. c. Larger cells with larger nuclei and nucleoli. d. Division of nuclei. e. Club-shaped cells in close apposition (cell-division?). C. Cells with an endogenous brood. 300 diameters.

and afterwards to mingle with the blood as colourless blood- or lymph-corpuscles. The more the glands become enlarged, the more numerous are the cellular elements which pass into the blood, and the larger and more perfectly developed are the individual colourless cells of the blood wont to be.

The same condition seems to prevail in the spleen. Originally we all imagined that the veins were the channels by which the colourless corpuscles were conveyed away from the spleen; but in this instance also 1 have come to the conclusion that their removal is in all probability effected by means of the lymphatic vessels.

LECTURE IX.

MARCH 13, 1858.

PYEMIA AND LEUCOCTTOSIS.

Comparison between colourless blood, and pus-corpuscles.—Physiological reabsorption of pus; incomplete (inspissation, cheesy transformation), and complete (fatty metamorphosis, or milky transformation). Intravasation of pus.

Pus in the lymphatic vessels.—Retention of matters in the lymphatic glands —Mechanical separation (filtration).—Coloration by tattooing.—Chemical separation (attraction): Cancer, Syphilis.—Irritation of lymphatic glands, and its relation to leucocytosis.

Digestive and puerperal (physiological) leucocytosis.—Pathological leucocytosis (Scrofulosis, typhoid fever, cancer, erysipelas).

Lymphoid apparatuses: solitary and Peyerian follicles in the intestine.—Tonsils and follicles of the tongue.—Thymus.—Spleen.

Complete rejection of pyaemia as a dyscrasia susceptible of demonstration morphologically.

In a practical point of view the question oipycemia forcibly obtrudes itself upon us in connection with the changes which we have last considered, and as this must still be reckoned among the most controvertible of subjects, you will, I hope, allow me to enter a little more particularly into its details.

What is to be understood by pyaemia? It has generally been conceived to be a condition, in which the blood contains pus, and as pus is essentially characterized by its morphological constituents, what is meant of course is, that pus-corpuscles are to be seen in the blood. Now that we have found out, however, that the colourless corpuscles of the blood as they usually appear and are to be observed in people in the best state of health, resemble pus-corpuscles in every respect (p. 148), one essential point in the question is thus at the very outset got rid of. In order, however, to render the subject to some extent perspicuous, it is necessary to enter into the consideration of the different points of view which are here involved a little more in detail.

Colourless blood-cells are so like pus-corpuscles as easily to be mistaken for them, so that if in any specimen we meet with such elements, we can never say with certainty off-hand whether we have to deal with colourless blood-, or pus-corpuscles. Formerly, and to some extent even up to our own times, the view was very generally entertained that the constituents of pus pre-existed in the blood; that pus was only a kind of secretion from the blood, in somewhat the same way that urine is; and that it could also like a simple fluid return into the blood. This view explains, you see, the conception which has been so long preserved in the doctrine of the so-called physiological reabsorption of pus.

It was imagined that the pus might be again taken up into the blood from the different points at which it had been deposited, and that a favourable turn was thereby effected in the disease, inasmuch as the reabsorbed pus was thus at last removed from the body. The tale went that in the case of a patient with pus in the cavity of the pleura the disease might terminate in the evacuation of purulent urine or purulent faeces, without the pus having previously made its way directly from the pleura into the urinary passages or the intestinal canal. It was therefore admitted to be possible that pus might be reabsorbed and conveyed away in substance. Afterwards, when the doctrine of pyasmia had more and more gained ground, these cases

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