160 HUMAN PHYSIOLOGY. 



mental development, is associated with, if not directly dependent on, 

 a congenital absence or an arrested development of the thyroid, 

 either at the time of birth or during the early years of childhood. 



Myxedema, a condition of the skin in which there is a hyperplasia 

 of the connective tissue, of an embryonic type, rich in mucin, is 

 generally regarded as one of the effects of degenerative processes in 

 the thyroid. Partly in consequence of this change in the skin the 

 face becomes broader, swollen, and flattened, giving rise to a loss 

 of expression. At the same time the mind becomes dull, clouded, 

 even approximating the idiotic type. This supposed infiltration of 

 the skin with mucin was termed myxedema by Ord, who at the same 

 time associated it with a change in the structure of the thyroid as a 

 result of which it became functionally useless. 



Extirpation of the thyroid, for relief from symptoms due to grave 

 pathologic changes, has been followed in human beings by symptoms 

 similar to those of myxedema. To this condition the terms operative 

 myxedema and cachexia strumipriva have been applied. 



After the publication of the history of the myxedema which fol- 

 lowed surgical removal of the thyroid, Schiff, in 1887, repeated his 

 earlier experiments on dogs, and found again that removal of the 

 thyroid was speedily followed by tremors, convulsions, and death. 

 Similar experiments were made by Horsley on monkeys, with results 

 which resembled those characteristic of myxedema. Among the 

 symptoms which developed within a few days after the removal of 

 the gland may be mentioned loss of appetite ; fibrillar contractions 

 of muscles ; tremors ; spasms ; mucinoid degeneration of the skin, 

 giving rise to puffiness of the eyelids and face and to a swollen con- 

 dition of the abdomen ; hebetude of mind, frequently terminating in 

 idiocy ; fall of blood-pressure ; dyspnea ; albuminuria ; atrophy of the 

 tissues, followed by death of the animal in the course of from five to 

 eight weeks. The complexus of symptoms observed in monkeys was 

 divided by Horsley into three stages : viz., the neurotic, the mucinoid, 

 and the atrophic. It is evident that the presence of the thyroid is 

 essential to the normal activity of the tissues generally. As to the 

 manner in which it exerts its favorable influence, there is some differ- 

 ence of opinion. The view that the gland removes from the blood 

 certain toxic bodies, rendering them innocuous, and thus preserving 

 the body from a species of auto-intoxication, is gradually yielding to 

 the more probable view that the epithelium is engaged in the 

 secretion of a specific material, which finds its way into the blood 



