1886.] 



On the Function of the Thyroid Gland. 



7 



place, it aids in the manufacture of blood-corpuscles. My researches 

 during the past year (1885) have been directed towards the investi- 

 gation of (1) the circumstances which influence the course of the 

 extensive disturbance of general nutrition which follows the loss of the 

 gland ; (2) the direct effect of the said fall in nutrition upon the 

 nerve-centres ; and (3) the haemapoietic function of the gland. 



(1.) I find that the determining factor par excellence of the value of 

 the gland as regards its influence on the general metabolic processes of 

 the animal is Age. The effect of removing the gland in the young 

 animal is the rapid appearance of violent nerve symptoms and death 

 in a few days; in a rather older animal, i.e., a one-year old dog, the 

 symptoms are less violent, later in their appearance, and the animal 

 survives perhaps for a fortnight or three weeks ; in a very old animal 

 the removal of the gland simply hastens the torpor of old age ; these 

 observations refer to dogs and cats. In the higher animals, monkeys, 

 the operation on a young individual produces the same result as in a 

 young dog, but, as I showed last year, an older animal, if kept under 

 ordinary circumstances, will survive for six or seven weeks, dying at 

 the end of that time of myxcedema. On the whole, therefore, it 

 appears that the thyroid gland is of extreme importance when tissue 

 metabolism is most active, and that it diminishes as the senile state 

 advances. Huschke has shown that the relative weight of the 

 thyroid body to the body weight is greatest at birth, that it rapidly 

 diminishes during the next few weeks, and that it steadily decreases 

 as age advances. Finally, the structural degeneration of the gland in 

 old age is well known. It is clear, therefore, that the gland plays an 

 important and constant part in the metabolism of the body; I desire 

 here to draw special attention to the fact that the symptoms of old 

 age, namely, wasting of the actively functional parenchymatous 

 tissues, atrophy, and falling out of the hair, decay of the teeth, dryness 

 and harshness of the skin, tremors, &c, are exactly the most prominent 

 features of the myxcedematous state, whether it occurs naturally in 

 the human being, prematurely, as in cretinism, or artificially, as in 

 my experiments on monkeys. It is, perhaps, well to remark here 

 that, as might have been foreseen, the previous state of nutrition of 

 the body determines to a large extent the rapidity of onset and the 

 course of the symptoms. 



The next circumstance of extreme importance which influences the 

 course of the symptoms is the Temperature at which the animals are 

 kept after the gland has been removed. I showed last year that one 

 of the most obvious features of the fall of nutrition which follows the 

 loss of the gland was a steady diminution of the body heat, this sug- 

 gested to me a line of research which has yielded a striking result. I 

 have kept another series of animals (on whom I have performed 

 thyroidectomy under the conditions above stated) at a constant tern- 



