The Action of Tliyroid upon the Organs of the White Rat 235 



The rats recorded in Table \'. ai^ree mure closely with the nieasureiiu iits 

 of the Wistar Institute rats. It is possible that my observations on the 

 length of the animals have not been taken strictly in accordance with 

 the routine method adopted in the Wistar Institute. Alterations in the 

 position of the animal readih' alter the observed length, and my measure- 

 ments may have been taken with too little extension of the body and neck. 

 The measurement shrinks a little after rigor mortis has set in, but my 

 records were always taken immediately after death when the muscles are 

 lax. As the same relative difierences are noted in both the control and 

 thyroid-fed animals, this does not alter their value for compariscjn with one 

 another, but a comparison with the Wistar Institute rats is not so satis- 

 factory. The weights of the individual organs compared with the body 

 weiirht show a orreater resemblance to the weights recorded in Donaldson's 

 tables. Difierences are noted later in the description of changes in the 

 individual organs resulting from thyroid-feeding. It is possible, of course, 

 that the rats bred in this part of the world have their own characteristic 

 features. There are certainly peculiarities in individual organs, such as 

 the spleen and liver, which differ widely from those noted in the Wistar 

 Institute. 



III. Results Obtained. 



(a) Effects of Thyroid on the Growth of the Body. 



Considerable variations in growth are apparent both in the control and 

 thyroid-fed animals, male and female. Some of the controls received small 

 doses of fresh ox flesh, but with no obvious effect upon the rate of their 

 crrowth. The thyi-oid-fed male animals in Table IV. increased in weight 

 fairly uniformly, but as the corresponding initial weights of the control 

 animals were not recorded, no definite comparison can be made between 

 them. It can only be said that the thyroid did not perceptibly increase or 

 check the rate of growth. In Table V. a comparison can be made ; the 

 control i-ats gained an average of 69 grm. in twenty-iive days, while the 

 animals under the influence of a daily dose of 0'2 grm. thyroid gained an 

 average of 65 grm. in the same time. The control animals, therefore, 

 gained slightly more than the thyroid-fed animals. The same is true of 

 the female rats. Tables VII. and VIII., in which the controls gained on the 

 average 2 grm. more than the rats receiving 0"1 grm. fresh thyroid daily. 



The average among the females is made up of widely differing figures. 

 Some rats appeared to thrive and put on weight under the influence of 

 thyroid much better than their controls ; in other animals a decided check 

 was imposed on their growth by thyroid-feeding. In a few instances 

 thyroid appeared to stimulate a more rapid growth which was later 

 followed by an actual decline in weight, and some of the final figures of 

 weights of the thyroid-fed animals are less than the weights attained at 

 an earlier stage of the experiments. Some of the animals died while under 

 the influence of thyroid ; one of them, a female, lost weight from the first 



