The Action of Thyroid upon the Organs of the White Rat 245 



In tlie males examined the increase of weight of the pituitary of the 

 thyroid-fed animals is 18 per cent, per 100 grm. body weight, but measured 

 in terms of body length the thyroid-fed pituitary shows a decrease of 

 18 per cent, compared with that of the controls. The comparison in terms 

 of Ixxly ItMigth is probably more accurate where much weight has been lost 

 during the period of thyroid-feeding, as was the ca.se in these animals. The 

 experiments are not numerous enough to settle this matter, but as far as 

 they go they tend to show that thyroid-feeding also checks the growth of 

 the male pituitary. 



The diminished size of the pituitary body seems to be chiefly accounted 

 for by a delay in growth of the pars glandularis. There is considerable 

 change in this lobe, and a notable deficiency in the number of the 

 characteri.stic large granular cells. 



IV, Discussion of Results. 



It is generall}' agreed that the thyroid glands contain some substance 

 or substances which, when liberated into the body, promote metabolism. 

 A condition of hyperthyroidism may be set up by excessive activity of 

 the thyroid glands themselves or by the administration of thyroid in the 

 food. In the latter case the thyroid glands of the animal appear to 

 take little or no part in the production of the hyperthyroidism. They 

 are smaller than those of the control animals and show signs of relative 

 inactivity. 



A small degree of hyperth3'roidism may, in a young animal, to some 

 extent accelerate the growth of the body, but in doses of O'l to 02 grm. 

 fresh thyroid given daily tends rather to check the increase of w^eight 

 in growing rats. Individual variations occur, but I am inclined to agree 

 with Hoskins in this respect. Little or no alteration is produced in the 

 body length, but there is, on the whole, a diminution of body weight. 

 Thyroid-feeding, moreover, gives rise to profound changes in the body, 

 and if long continued in the amounts mentioned brings about fatal results. 



Thyroid acts upon the metabolism of the body as a forced draught 

 acts on the fuel in a furnace. The thyroid glands, indeed, may be aptly 

 compared with the draught-regulating mechanism of a furnace. Excess of 

 thyroid leads, as Cramer and Krause (3) showed, to a rapid disappearance 

 of glycogen from the liver, and of fats from the body generally. At the same 

 time many of the organs are increased in w^eight and show signs of increased 

 activity. The loss of fat may be, and sometimes is, more than balanced by 

 the increased weight of some of the viscera. Hoskins explains the hyper- 

 trophy of organs resulting from thyroid-feeding as simply due to increased 

 metabolism. He points out the similarity which exists between his figures 

 and those obtained by Hatai (7) in white rats subjected to a large amount 

 of exercise. Hatai kept rats during the daytime in revolving cages which 

 necessitated their continual activity. After periods of three to six months 



