238 Herring: 



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of this weiorht Donaldson's normal figure for the heart is about 0'745 orrm. 

 Among the control rats in Table III., No. 6, a larger animal weighing 

 200 grm., and having a body length of 193 mm., has a heart which weighs 

 0'754 grm. This figure corresponds very well with Donaldson's normal, 

 and is, indeed, slightly less per unit body weight. The size of the heart 

 of the thyroid-fed animal is more than trebled, and its weight is 230 per 

 cent, above the normal. This rat was fed on 02 grm. fresh ox thyroid 

 daily for fifty-one days. Among the females the heaviest heart is also 

 found in the animal which received the largest amount of thyroid. This 

 rat (No. 7, Table VIII.), with a body weight of 138 grm., and a length of 

 174 mm., has a heart weighing 1*187 grm., and received 0*1 grm. of thyroid 

 daily for forty-six days. The normal weight of the heart of a female rat 

 of this size is about 600 grm., the gain of weight, therefore, in the thyroid - 

 fed animal is about 98 per cent. These are the extremes, but the averages 

 are also high. The increase in weight of the heart of the thyroid-fed 

 males averages 123 per cent., and of the thyroid-fed females 59 per cent. 

 If the weights of the heart per 100 mm. body length be compared, the 

 figures are not much altered. The male thyroid-fed animals show an 

 increase of 116 per cent., and the females an increase of 65 per cent. 



In both male and female rats the heaviest hearts are in the animals 

 which received most thyroid. The female heart is normally heavier than 

 the heart of the male of the same body weight. The females received less 

 thyroid than the males, and their hearts are not so greatly hypertrophied. 

 The degree of hypertrophy of the heart is much greater than that noted 

 by Hoskins. He obtained a hypertrophy of 16"7 to 24"6 per cent, in 

 females, and of 15'4 to 36 per cent, in males. As already stated, the doses 

 of thj^roid he used were smaller or given at less frequent intervals. 



The increase in size affects the whole heart, and the naked-ej^e appear- 

 ance is very striking. The ventricles are large and muscular. On section 

 the increased thickness of their walls is apparent, that of the left ventricle 

 being particularly so. Microscopical examination shows an increase in 

 muscular fibres, and an apparent increase in size of many of the fibres. 



3. The Kidneys. — The kidneys also are constantly and greatly hyper- 

 trophied by thyroid-feeding both in male and female rats. 



The weights of the kidneys of the control animals agree fairly well 

 with Donaldson's figures per unit body weight, but are somewhat heavier in 

 the males of my series and lighter in the females. The greatest changes 

 are again noticed in the rats which received most thyroid. The last male 

 rat in Table IV. shows a weight of 4758 grm. for both kidneys. This rat 

 has a body weight of 182 grm. and a length of 189 mm. Donaldson's 

 average weight for the kidneys of an animal of this weight is about 

 1"574 grm. Among the control animals of Table III., No. 6, a larger rat, 

 has a kidney weight of 1388 grm. The weight of the kidneys of the 

 thyroid-fed rat is more than trebled, the increase against Donaldson's 

 figure being 201 per cent., and against the control 214 per cent. 



