316 THE DUCTLESS GLANDS 



feeding increase the colloid in the thyroid. Thyroid feeding 

 inhibits the growth rate of the thyroid while iodide does not. 

 Similar effects were obtained in experiments upon rabbits. 

 Since among all the. organs and tissues of the body thyroid 

 alone produces a definite effect and since iodide does not pro- 

 duce this effect, it is suggested that decreased rate of growth, 

 hypertrophy of liver, heart, kidneys, and adrenals, and rela- 

 tively decreased thyroid may be used as tests for preparations 

 alleged to be the essential thyroid secretion. According to 

 more recent observations of Cameron, Kendall's thyroxin 

 produces effects similar to those of thyroid when given by the 

 mouth. But quantitatively, compared on a basis of iodine 

 content, the effects of thyroxin are distinctly less than those 

 of desiccated thyroid. This is probably due to bacterial 

 decomposition ; thyroid acts as a shield. The hypertrophy of 

 heart and lymphatic tissue resembles that observed in cases 

 of hyperthyroidism. 



Many attempts have been made to induce symptoms of 

 exophthalmic goitre by means of the administration of thyroid 

 substance to animals. It is doubtful whether a condition 

 strongly resembling Graves's disease has ever been brought 

 about by such methods. But there can be little doubt that 

 definite toxic effects can be produced by thyroid feeding. 

 These are loss of body weight, gastro-enteritis, and diarrhoea, 

 rather than tachycardia, nervousness, and exophthalmos. 

 Kendall believes that in order to get " hyperthyroidism " we 

 must have thyroid and adrenal cortex acting together. It 

 has not yet been determined how far the toxic symptoms just 

 described are due to iodine qua iodine. 



O. The Effects of Thyroid Gland, and Preparations 

 made from it, upon Metabolism 



Many years ago it was observed that myxcedematous sub- 

 jects, when treated with thyroid, suffered loss of weight due 

 to reduction of fat and water. Since then various thyroid 

 preparations have been employed to reduce obesity. 



When systematic metabolism experiments were carried out 

 it was usually found that thyroid causes an increase of nitrogen 

 in the urine, showing increased ^protein metabolism. The 

 same or similar results were obtained with "iodothyrin " and 



