EXTRACTS OF THE THYROID 57 



We learn, then, from these observations that thyroid- 

 ectomy may cause an increase in the secretory activity 

 of all parts of the pituitary body 1 . 



PHYSIOLOGICAL EFFECTS OF EXTRACTS OF THE THYROID 



The immediate effects of injections of extracts of the Effects of in- 

 thyroid have been investigated by a number of observers, thyroid ex- 

 who are unanimous in the opinion that there is a sudden tracts. 

 slight fall of blood-pressure due to dilatation of the 

 peripheral vessels. 



Further, it has been found by Hick and myself 2 

 that, in spite of this fall in the blood-pressure, the force 

 and tone of uterine contractions is considerably increased, 

 and that these become considerably augmented after 

 repeated doses, until general convulsions with violent 

 spasms of the uterus are produced. 



Itagaki 3 has also observed the effect of thyroid 

 extracts, intravenously injected, on the uterus, and has 

 concluded that these extracts occasionally produce an 

 increase of tone, but that often they have no effect at 

 all on the uterus. This contradictory statement may 

 probably be explained by the fact that the sensitiveness 

 of the uterus in the lower animals varies considerably 

 according to the season. 



The effects of injections of thyroid extract on lactation 

 will be mentioned later (see p. 93). 



Feeding experiments. — An enormous amount of work Effects of 

 has been done in regard to the effects produced by^dtS- h 

 feeding with thyroid extracts. It is, therefore, well tracts. 

 known that thyroid extracts can influence profoundly 

 the general metabolism, and that in hypothyroidism 

 feeding with thyroid gland will compensate the deficiency 

 of natural secretion; and that, moreover, by the 

 administration of excessive doses the symptoms 

 of hyperthyroidism — wasting, tachycardia, muscular 



1 Bell, W. Blair, The Pituitary, 1919. 



2 Bell, W. Blair, and P. Hick, Brit. Med. Journ., 1909, vol. i, p. 777. 



3 Itagaki, M., Quart. Journ. Exper. Physiol, 1917, vol. xi, p. 39. 



