sate actively. This form of goiter is met with as the important pathologic condition of many cases of Graves' disease (see page 582).

Secondary Changes.-The thyroid frequently suffers secondary changes in goiter. The hyperplasia of connective tissue between the acini has been referred to. Sometimes this becomes so considerable that the term fibrous goiter is warranted. Cystie formations have also been mentioned, the cysts referred to result

ing from the confluence of the dilated acini. The contents in such cases consist of colloid material or of more or less serous or hemorrhagic liquid. Occasionally cysts result from hemorrhage in degenerated parts of the gland, with subsequent absorption of the blood, and exudation of serous liquid. The contents in such cases may be purely serous or may consist of brownish grumous matter containing abundant cholesterin. Very rarely secondary proliferative changes occur in the walls of the cyst, causing papillomatous projections. Calcification is a very common terminal change in degenerated goiters. It may occur in isolated areas, or may

cause a uniform hardening of the gland. Actual ossification has been observed.

Mechanical Effects of Goiter.-The enlarged gland presses upon the adjacent structures more or less seriously. The trachea is most frequently compressed or dislocated from its median position. Pressure upon the large veins may occasion passive congestions and edema; and less commonly pressure on the carotid artery may interfere with the circulation of blood in the brain. The nerves in the vicinity (vagus, recurrent laryngeal, and sympathetic) are likewise exposed to compression.

INFECTIOUS DISEASES.

Tuberculosis may occur in the form of miliary tubercles or as small caseous nodules.

Syphilis is met with in the form of gummata.

Actinomycosis is a very rare disease of the thyroid gland.

TUMORS AND PARASITES.

Tumors. The term malignant struma is sometimes applied to tumors, and it is difficult in certain cases to draw a sharp line be tween certain goiters and distinct new-growths (adenomata).

The term adenoma, however, should be restricted to cases in which the proliferation of acini is more or less atypical, and in which the tumor is circumscribed, nodular, or otherwise distinguishable from the pre-existing gland-tissue. Sometimes tumors of the thyroid having typically adenomatous characters give metastasis.

Carcinoma may occur in the form of a nodular, or more diffuse tumor. Metastasis is frequent in cases of carcinoma, but also occurs in cases that present the appearances of an ordinary adenoma. The bones are frequently involved by metastatic deposits. Extension from the thyroid to the adjacent organs is not infrequent.

Sarcoma occurs in several varieties. Round-celled sarcoma and angiosarcoma are particularly malignant.

Secondary tumors in the thyroid are rare.

Parasites.-Echinococcus-cysts have been met with, but are

very rare.

GENERAL RESULTS OF THYROID DISEASE.

The physiology of the gland has not as yet been fully determined, though certain facts have become established. The old authors believed the gland to be active as a blood-making organ, and this is still maintained by some. It is, however, unlikely that this function is an important one. The frequent association of thyroid disease with certain general conditions (cretinism and myxedema) has led to experiments upon animals that have established certain important facts.

The immediate removal, by operation, of the entire thyroid gland causes severe nervous manifestations resembling those of tetany followed by rapid death. Partial removal of the gland causes comparatively trivial consequences, but in cases in which total ablation has been practised, and in which a certain amount of thyroid influence has been kept up by injections of thyroid extract or the feeding of thyroid gland, marked symptoms have been found to develop after a period of some months. Among these symptoms are pallor, edema of the skin, general weakness, disturbances of growth, and alteration of the cerebral functions (intellection, sensation, and motor power). This condition has been termed cachexia strumipriva, and its resemblance to cretinism and myxedema will be apparent from a reference to the symptoms of those diseases.

Cretinism.-Cretinism is a peculiar disease, occurring with great frequency in certain parts of central Europe, especially in Switzerland, and not infrequently in other parts of the world. The thyroid gland is sometimes atrophic, and sometimes goiterous, but in all cases diseased. The disease is not, as a rule, present at birth, but usually develops soon after birth; and the parents may be cretinoid or goiterous. Sometimes healthy parents have cretin children. The cretin remains physically and mentally undeveloped; the subcutaneous tissue is flabby, abundant, and sometimes distinctly myxedematous (Fig. 266); the head is large; the lips and tongue enormously thickened, and the latter usually protrudes from the mouth; the hairs of the body are little developed. Myxedema.-Myxedema is a disease that develops in later life; sometimes after distinct diseases of the thyroid (goiter, gumma, tumors, etc.), but often without any manifest disease of thyroid, though atrophy and degenerations (calcifi- myxedematous condition of hands cation) may be disclosed by the post-mortem examination. There is a peculiar swelling of the eyelids and of the subcutaneous tissue of the face and neck, and subsequently the same change occurs elsewhere, involving the limbs and the entire body. The appearances at first suggest edema, but there is not the usual pitting on pressure, and the feeling conveyed to the hand is that of an infiltration with some form of gelatinous tissue. This has been found to consist of a mucin-like substance, often associated with increase of the adipose tissue itself. The skin of the patient is pallid and exceedingly dry; the hair falls out, and nervous symptoms are developed. Eventually intellection may be almost destroyed.

The resemblance of these diseases to the symptoms produced by operative removal of the thyroid gland makes it certain that disease of the thyroid is the fundamental condition in cretinism and myxedema. This fact is still more clearly demonstrated by the numerous cures of these diseases following implantation of sheeps' thyroids in the peritoneal cavity, and especially the feeding of thyroid-gland tissue or extracts.

Graves' disease has been referred to in connection with goiter. The cardinal symptoms of this disease are enlargement of the gland, palpitation of the heart, exophthalmos, and muscular tremor. The pathology of the disease has not as yet been fully determined. It seems likely, however, from recent investigations that the thyroid disease, from whatever cause it may result, is the primary disorder. Removal of large parts of the gland has been found to control the symptoms of Graves' disease in a large number of cases, and the feeding of thyroid extract for a long period of time produces symptoms like those of Graves' disease: rapid action and palpitation of the heart, exophthalmos, and tremor. According to the view here expressed, the symptoms which together constitute Graves' disease are probably due to overproduction of thyroid secretion; they are, in fact, the result of hyperthyroidism. The opinion, however, is held by others that Graves' disease is primarily an affection of the nervous system.

THE SUPRARENAL BODIES.

Anatomic Considerations.-The suprarenal bodies are composed of a cortical and a medullary portion, and are enclosed in a fibrous capsule from which septa extend into the substance. The cortical portion is composed of aggregations of polygonal cells which frequently contain fat-droplets. Three layers are distinguishable in the cortex: an outer zone, in which the cells are arranged in oval masses; a middle zone, in which they form cylindrical columns extending toward the medullary; and an inner zone, composed of irregularly anastomosing columns of cells. The cells of the middle zone are deeply pigmented and contain abun dant granular and globular fat. The medulla of the gland consists of similar polygonal cells arranged in cords or irregularly anastomosing columns. Between these are found large venous channels and numerous non-medullated nerve-fibers, together with ganglioncells. The fibrous septa of the gland contain blood-vessels and lymphatics.

CONGENITAL ANOMALIES.

Accessory suprarenal bodies may be found in the vicinity of the main body. Of peculiar interest are the portions of suprarenal tissue found in the capsule or cortex of the kidney. These "rests" may subsequently proliferate and form tumors of the kidney (see Tumors of the Kidney).

Occasionally the suprarenal bodies are found in unusual situ

ations.

DEGENERATIONS.

Fatty degeneration is normal in adults. It affects the cortex, giving this layer a yellowish color. The substance of