All lymphatic vessels connect themselves directly with lymphatic glands, so that no lymph passes into the circulation without first traversing a lymphatic gland. Dissolved substances introduced into the lymphatic spaces of the skin and subcutaneous tissue are rapidly carried up the lymphatics and through the glands into the general circulation; this is matter of experience every day in the subcutaneous injection of medicinal agents. Granular material, however, does not pass through the glands, which form a filter for all solid particles.
The apparatus by which the Filtration of the lymph is effected is illustrated in Fig. 261. When the afferent lymphatic vessel coming from the periphery reaches the gland, it first forms a plexus in the capsule. On the other hand the efferent vessel emerges from a plexus of vessels at the hilus, and this plexus is connected with the medullary portion of the gland. In passing from the afferent to the afferent vessel the lymph traverses a series of sinuses, c, c, in figure. The sinuses are not clear spaces, but contain a reticulum or mesh-work shown in the figure. These sinuses surround the proper glandular tissue, which is in the form of rounded follicles or cords composed of densely packed lymph cells (a, a, in figure). The lymph first passes from the afferent plexus into the sinuses of the cortex, then into those of the medullary part, where originate the radicles of the efferent vessel. The sinuses being occupied by the fine reticulum will catch solid particles brought to the gland, and such particles will therefore be most readily caught at the cortical portion of the gland.
In the normal gland, according to the researches of Flemming and Baumgarten, there is an active new-formation proceeding by means of Karyomitosis. This occurs at a number of centres in the cortex, whose cells are less deeply stained than those elsewhere, but in which the nuclear figures of karyomitosis are visible. There is also nuclear division in other parts, but to a less degree. These appearances probably indicate the new-formation of leucocytes.
In the operation of Tattooing granular pigment, such as Indian ink or vermilion, is introduced into the skin. Part of it remains permanently in the corium, but part is conveyed up the lymphatics and is caught by the glands, where it remains fixed.
So it is in pathological conditions. The lymphatic glands are very frequently associated in morbid processes which are occurring in parts in which the vessels passing to the glands take origin. Dissolved and solid materials are thus conveyed to the glands, and according to the nature of the material will affect the gland or not. In Septic inflammations, for example, the microbes are often conveyed to the glands and produce inflammation there. As these are in the form of fine particles they are arrested at the gland, and the inflammation makes a pause there only to proceed further, if the organisms propagate onwards. But even in the case of Simple inflammations, although the products are for the most part dissolved, still they are frequently of an irritating nature and the glands inflame. We have seen also that solid material from cancers is often conveyed along the lymphatic vessels and is caught at the glands.
In all these cases the material may produce no irritation in the lymphatic vessels along which it is being conveyed. If concentrated or very virulent it will do so, but it often does not, and in that case a wide interval of healthy structure intervenes between the primary disease and the lymphatic gland. Hence it is common to speak of the disease being conveyed to the glands by metastasis. Indeed, most of the lesions to which the glands are liable are secondary to diseases elsewhere, but there are some which may be regarded as idiopathic.