WE have already had occasion to observe that the lymphatic system is intimately related to the blood-vascular system, and may be regarded as a part of it. We have also seen that this system nas close relations to the connective tissue, the spaces in the latter being lymph spaces lined with endothelium and having direct connections with the lymphatic vessels. Wherever there is increased exudation from the blood-vessels the serous spaces and lymphatic vessels are distended, and the current through them increased. We have seen this to be the case in inflammations and oedemas.

Inflammation Of The Lymphatics. Lymphangeitis

The lymphatics are liable to inflammations of a more independent kind, and warranting the name lymphangeitis. In order to such inflammation there must be in the vessels some irritant, and the irritant is similar to that which we find in the veins in suppurative phlebitis, namely, a septic poison. Just as in the case of veins there is a thrombosis wjth suppurative inflammation (see thrombo-phlebitis), so here there is a coagulum formed which breaks down as suppuration goes on. In connection with wounds which have been exposed to decomposing juices, such as dissecting wounds, we sometimes find the course of the lymphatic vessels marked by red streaks in the skin. These represent inflamniation of the lymphatics and surrounding connective tissue. The inflammation not infrequently goes on to suppuration, so that abscesses form at intervals in the course of the vessels. Here also, as in thrombophlebitis, there is a transportation of the septic matter, but it is caught by the lymphatic glands, which are liable to suppuration in consequence.

Erysipelas and other phlegmonous inflammations of the skin are inflammations, primarily of the lymphatics and of the serous spaces which form the radicles of the lymphatics. Microbes are present in the lymphatics of the skin in such cases (see under Diseases of the Skin), and they may be so numerous as to render the lymphatic vessels as well as the serous spaces peculiarly prominent, when the sections have been stained by aniline dyes. The phlegmonous inflammation of the parotid, which occasionally occurs in cases of septic wounds, is probably of a similar nature. Epidemic parotitis (mumps) may perhaps be placed in the same category.

We have already seen that Elephantiasis frequently begins in recurrent attacks resembling erysipelas, in which the lymphatic vessels are obviously engaged. There are often red streaks passing up the limb, and the lymphatic glands may be enlarged. The irritation here is slighter and more chronic. The inflammation results in great thickening of the connective tissue, but there is often along with it dilatation of the lymphatic vessels, so that, when the part is cut into, an abundant lymphatic fluid exudes which sometimes contains fat.

Tuberculosis Of The Lymphatics

This is very frequent in connection with tuberculosis of various parts. Thus in tuberculosis of the intestine there are often visible beneath the peritoneum prominent white cords which are tuberculous lymphatics. In the lungs- also tuberculosis frequently extends by the lymphatics. The Thoracic duct is sometimes the seat of a regular tubercular eruption in general tuberculosis. (Orth).

Lymphangiectasia

The lymphatic vessels are occasionally the seat of dilatation. Obstruction of a lymphatic stem may produce a varicose dilatation of the vessels and even their rupture. The most striking examples of this are afforded by Obstruction of the thoracic duct. This is not an infrequent accident, arising from various causes, such as pressure of tumours, aneurysms, etc., in its neighbourhood, but more particularly from thrombosis of the jugular and innominate veins (see under (Edema and Dropsy). Experiments on animals show that ligature of the duct leads to dilatation and sometimes to rupture of its dilated origin in the abdomen, which forms the Cysticerna chyli (Cooper). In man there may be a similar rupture, either in the abdomen or pleura, leading to accumulation of fluid in these cavities.

As the fluid in the thoracic duct contains fat, the exudation in the peritoneum or pleura will be chylous (see Chylous Ascites and Hydro-thorax). Rupture is, however, only an occasional result of obstruction of the duct, as the anastomosing connections may compensate, so that there may even be comparatively little dilatation. We have already seen also that when the lymphatics are obstructed by the ova of the filaria sanguinis, Lymph-scrotum, Chyluria, etc., may result. In the enlargement of the tongue called Macroglossia, which is frequently congenital, there is commonly a great dilatation of the lymphatics, which may form considerable cysts. Sometimes the whole lesion has the aspects of a tumour-formation.

Tumours Of The Lymphatics

There is sometimes a localized dilatation of many lymphatics so as to form a distinct Vascular tumour. These tumours are usually cavernous in structure, and are classed as Cavernous lymphangiomas. Sometimes they develop actual cysts, which are filled with serous fluid, and are designated Hygromas.

We sometimes find lymphatic vessels dilated in the neighbourhood of a Cancer, the material in the vessels being derived from the tumour. This occurs mostly in the case of cancers which are undergoing softening. It is most frequently seen in connection with mammary cancers, where the lymphatics may have the form of firm cylinders as large as quills, filled with white material. The same thing is seen in the case of secondary cancer of the lung, where there are nodules immediately under the pleura. The subpleural lymphatics around the nodule are found, as it were, injected with white material. So is it sometimes in the capsule of the liver when cancerous nodules. are near the surface.- These naked-eye appearances indicate how prone cancerous material is to pass into the lymphatics, and, under the microscope, at the margins of a growing cancer the lymph-spaces may sometimes be found filled with the epithelial masses. (See under Cancer).

Literature

Velpeau, Arch. gen. cle med., 1835, viii.; Beeschet, Le systeme lymphatique, 1836; Carter (Lymphangiectasis and Elephantiasis), Trans, of Med. Soc. of Bombay, 1861; Israel, Ueb. Lymphangioma, 1885; Bradley, Injuries and dis. of lymphatic system, 3rd ed., 1875; Cooper, Med. records and researches, 1798; Bogehold (Injuries of thor. duct), Arch. f. klin. Chirurg., xxix., 443; Coats, Museum Catal. of Western Infirmary (Obstr. of thor. duct from thrombosis of jug. vein, 2 specimens).