234 Herring 



appeared to affect growth, and is therefore not altogether desirable. 

 H OS kins avoided this objection but was able to do so in that he adminis- 

 tered thyroid at longer intervals. My rats took the greater part of their 

 food at night, and to ensure that each animal received its full dose of 

 thyroid the thyroid was finely minced and intimately mixed in the upper 

 layers of bread and milk more than sufficient for the twenty-four hours. 

 The thyroid was obtained fresh from the ox, and administered in daily 

 amounts of from 0*1 to 0*2 grm. Some of the control animals received 

 daily equivalent amounts of fresh ox flesh similarly minced and mixed 

 with the bread and milk. 



The weights of the animals were recorded weekly, and finally at the 

 end of the experiment. A thyroid-fed animal and its control were killed 

 by chloroform and bled by section of the large veins in the thorax. The 

 contents of the stomach, if any, were removed and weighed, and their 

 weight deducted from the weight of the animal. The final weights of the 

 animals recorded are therefore the net weights after deduction of the 

 contents of the stomach. The organs investigated were dissected out, 

 cleaned of fat and connective tissue, and weighed. In many cases the 

 adrenalin contents of the suprarenals were also measured by Folin's 

 method. Pieces of the organs were preserved in Zenker's fluid, cut and 

 examined. A complete account of the histological changes, however, is not 

 undertaken in this paper. 



Details of the records obtained are given in Tables III. to VIII. At the 

 foot of each table the average weights of the organs of the animals 

 employed are given, then the average weights per 100 grm. body weight, 

 and lastly the average weights per 100 mm. final body length. The body 

 length is the distance from tip of nose to centre of anus in the extended 

 animal after death. 



The organs investigated are the suprarenals, heart, kidneys, pancreas, 

 liver, and spleen in both male and female rats ; the thymus, thyroids, and 

 pituitary body in females only. The weights of the testes in males, and of 

 the ovaries and uterus in females, are also given. In Tables I. and II. the 

 average weights of the different organs in male and female of both the 

 control and the thyroid-fed groups are recorded for convenience of com- 

 parison in terms of average weights per 100 grm. body weight and per 

 100 mm. body length. In the animals in which the administration of 

 thyroid has notably interfered with the normal gain of weight of the body 

 as a whole, especially by the loss of fat, a comparison of the average 

 weights of the organs per unit body length probably gives one a more 

 exact figure of the changes which have taken place than does a comparison 

 in terms of body weight. Both methods are adopted in this paper. 



Individual differences in the relation between body length and body 

 weight are considerable in the rats examined in this laboratory. Com- 

 pared with Donaldson's tables (4), both the male and female rats show a 

 greater body weight per unit length than those of the Wistar Institute. 



