Читать книгу The Body at Work: A Treatise on the Principles of Physiology онлайн

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The third kind of breeding-place of leucocytes, a lymphatic gland, has a more elaborate structure than the tissues with which we have already dealt. Lymphatic glands are about the size of beans, and of the same shape. They are found in the course of lymphatic vessels in situations where they are not exposed to pressure, such as the back of the knee, the groin, the front of the elbow, the armpit, in the neck above the collar-bone, and on either side of the sterno-mastoid muscle, behind the angle of the jaw. There are a number in the abdomen and in the thorax. Each lymphatic gland is invested by a strong fibrous capsule. Its artery enters, and its vein and efferent lymphatics leave, the concave side (the hilus) of the gland. The lymphatic vessels which bring lymph to it pierce the capsule on its convex side. It is divisible into two parts: (1) The adenoid tissue which surrounds the artery and its branches; (2) the open network of “lymph-ways” which invest this adenoid tissue. Leucocytes divide in the adenoid tissue. The young lymphocytes drop out into the lymph-ways. As a stream of lymph, brought by the afferent vessels, is always flowing into the lymph-ways, and out by the efferent vessel or vessels, the lymphocytes are carried with it towards the thoracic duct. A lymphatic gland is therefore an organ for adding leucocytes to lymph in the course of the lymph-stream. It has, however, another and equally important function. Leucocytes which have picked up germs or other foreign matter pass on with the lymph to a lymphatic gland. After entering its lymph-ways they leave the lymph-stream, squeeze into the adenoid tissue of the gland, and there come to rest with their burden. They remain in the gland until the foreign matter is digested, or, if it be indigestible, until they undergo dissolution, when the particles of soot or pigment are deposited from their débris in a harmless state. When the skin is tattooed, much of the Indian ink and other pigment remains where it was inserted with the needle, but some of it is picked up by leucocytes and carried to the nearest lymphatic gland.