236 Herrincr 



to 



exhibition of O'l grm. thyroid, its control steadily gaining. These two 

 animals are not included in the returns. The fourth rat in Table VIII. 

 gained 15 grm. in thirty days, while its control gained only 8 grm. On the 

 other hand, the first rat in Table VII. gained 23 grm. in twenty-one days, 

 its sister under thyroid only gaining 1 grm. in the same period. Several 

 of the thyroid-fed rats died in their cages, one, a male, without any 

 previous loss of weight. Another male lost weight for several days before 

 death, and the females that died also lost weight, and several showed 

 symptoms of diarrhoea. None of the control rats showed any adverse 

 symptoms, and none died in their cages. 



The female rat appears to be more susceptible to the influence of 

 thyroid than the male. In all the thyroid-fed animals there is loss of fat, 

 sometimes to an extreme degree, and an absence of glycogen from the liver. 

 This loss of weight may be counterbalanced in part or wholly by increase 

 in the weight of other structures. The longest period over which thyroid 

 was given in these experiments was fifty-one days, and the dose 0"2 grm, 

 fresh thyroid daily. The animal, a male, throve well at first, but finally 

 died. Its organs show an extreme degree of change (Rat No. 7, Table IV.). 

 There was a complete absence of fat, but an enormous hypertrophy of 

 heart, kidneys, and liver — a condition probably incompatible with a 

 further prolongation of life. 



Hoskins, giving smaller doses, found that thyroid had little definite 

 influence on the growth of the body as a whole. 



My figures support his conclusions. No comparisons can be made as 

 regards alterations in length of body, as the initial lengths were not 

 recorded. In the male animals the average final body lengths are rather 

 greater in the thyroid-fed than in the controls. In the female rats the 

 lengths of both groups coincide. It is unlikely, therefore, that there is any 

 decided increase or check imposed on growth by thj^roid-feeding. 



Daily doses of O'l to 0"2 grm. of fresh ox thyroid are undoubtedly toxic 

 to white rats. They may not influence to any extent the growth of the 

 body as a whole, but they bring about changes in the body which 

 ultimately prove fatal. 



(b) Influence of Thyroid upon Individual Organs. 



1. The Suprarenals. — The suprarenal bodies are constantly increased 

 in size by thyroid-feeding both in male and female rats. The increase is a 

 rapid one, as is shown in Table VI., where the administration of 02 grm. 

 thyroid daily to young male rats has brought about an increase of 73 per 

 cent, in weight per 100 grm. body weight in eight days. 



Compared with Donaldson's tables, the weights of the suprarenals of 

 the male control animals average rather less per unit body weight than 

 those of the Wistar Institute rats. The suprarenals of the female animals 

 agree very closely with Donaldson's figures. The highest weight recorded 

 in the male thyroid-fed rats is 60 mg. in a rat weighing 148 grm. 



