In ague and other malarial diseases the spleen becomes remarkably enlarged ; and there is also great enlargement in a disease called leucocythmmia, in which the number of white corpuscles of the blood is enormously increased. (See DISEASES OF TUE BLOOD.) The Thyroid Gland is situated in the neck, and consists of two lobes or divisions, one on each side of the box of the windpipe, the two being connected by a cross-piece. (Fig. 133, p. 297.) It is usually larger in the female than in the male. Associated with it are smaller structures, two on each side, the parathyroids. The gland consists of a cap sule, sending in partitions which divide off the gland into spaces, occupied by round or oval sacs or vesicles, which are lined with cells and filled with glairy contents. The gland is richly supplied with blood-vessels. A great enlarge ment of it is the feature in goitre (Derbyshire neck), and a peculiar form of idiocy, called cretinism, is associated with it. Both of these diseases are discussed at pp. 287, 289.
The destruction of the true tissue of the thyroid in the human subject by disease, or its complete removal, produces a series of symp toms, of which solid swelling of the tissue in and under the skin, general muscular weak ness, as well as nervous changes, are the chief.
The features are altered by the general swell ing; enlargement of the hands and feet, as of the body generally, occurs. Such changes are best seen in the disease called myxoedema. (See Plate II.) In some animals complete re moval of the gland produces similar changes, attended by a rapidly fatal issue. When the symptoms occur in the human being, grafting the thyroid of an animal into the human body, or feeding the patient with fresh thyroid of the sheep or calf, or administering a glycerine extract of fresh thyroid, or even the dried gland in the form of tabloids, relieves the symptoms. It has been, therefore, concluded that the thyroid produces something to be added to the blood, the want of which causes the disease. It is certain that the dis ease myxoedema has become amenable to treatment since treatment by thyroid was introduced, and to some extent the disease called cretinism is capable of improvement by the same means. That this gland has some marked effect on the general nutrition of the body is also proved by the fact that thyroid feeding has been of use in obesity by stimulat ing the chemical changes of nutrition, and also in sonic skin affections, such as psoriasis, for a like reason.
On the other hand, overgrowth of the thy roid causes what is called hyperthyroidism, of which staring eyeballs, excessive rapidity of the heart, general tremor and nervous excita bility, are leading symptoms. (See Graves' Disease, p. 288.) The Thymus Gland also belongs to the blood glands. It also is placed on the wind pipe, but lower down than the thyroid, being in the upper part of the chest, behind the top of the breast-bone. It is in its period of greatest activity before birth, beginning to waste away soon after birth. Gradually the greater part of the gland disappears, its place being taken by connective tissue and fat, so that with the end of childhood little of it re mains. It consists, like the lymphatic gland,
of spaces inclosing adenoid tissue (p. 277). It is supposed to have to do with the elaboration of the blood, but nothing definite is known of its functions.
The Capsules are two small bodies connected with the kidneys. They are in shape not unlike a cocked hat, and one sur mounts each kidney. They are large before birth. In structure they are peculiar. The fibrous covering of the gland gives off divi sions, which pass inwards, dividing it off into spaces, some of which are circular, some oval, and some small and irregular. These spaces are filled with masses of large epithelial cells (p. 55). The blood-vessels ramifying between the groups of cells are very numerous, so also are the nerves. There is a disease, called Addison's disease, in which there is deep bronzing of the akin, supposed to be connected with diseased conditions of the supra-renal bodies. This disease is commented on at page 290.
These bodies are supposed to affect the quality of the blood in a way similar to the thyroid gland, either by removing some toxic substance from it, or by adding some material produced within it to the blood. Complete destruction of these bodies in an animal by disease, or complete removal by operation, is followed by intense muscular prostration, and symptoms like those of Addison's disease. Au extract of the capsules injected into the body produces very marked effects upon the blood vessels, by acting upon their muscular walls, causing them to contract, and so greatly diminishing their calibre. The smaller arteries are the vessels specially acted on, and so pro nounced may be the effect that for a time the flow of blood through the smaller vessels may be almost arrested, and some organs made almost bloodless. The effect lasts only a short time, however. But while it lasts the pressure of blood in the larger vessels is naturally greatly increased, because of the resistance to the flow in the smaller ones. This effect is easily seen locally, for a little of a watery extract introduced into the eye will male the lids and eyeball almost bloodless in a few minutes. This action is now largely taken advantage of for minor operations on eye, nose, and throat. For it has been found possible to extract from the juice of the fresh capsules of an animal the active principle to which this effect is due. To this active prin ciple the name Adrenalin has been applied. A small quantity of it applied as a spray to eye, nose, or throat, specially if combined with a small percentage of cocaine, enables one to perform a small operation quite painlessly and without blood. Thus tonsils may be removed without the least inconvenience to the patient, growths or obstructing spurs of bone may be removed from the nose, or small growths from the eyelids, while a similar combination is extremely useful in some acute inflammations of the eyelids.