58 THE ROYAL SOCIETY OF CANADA 



immediately after the animals were weighed. It was usually eaten 

 rapidly and completely. No other food was given till late in the 

 afternoon. Food residues were almost always present in the cages 

 next morning, indicating that excess had been given. The animals 

 were kept in exactly similar cages a little more than one cubic foot 

 in capacity, and under the same conditions of heating and lighting. 



Two thyroid preparations were used, one a Merck- Darmstadt 

 preparation containing 0.38 per cent, iodine, and at least 12 years 

 old, the second an Armour hog-thyroid preparation (December, 

 1919) containing 0.34 per cent, iodine. These will be subsequently 

 referred to as A and B They had been previously compared (2) and 

 found to produce very similar results on growth and organ-hyper- 

 trophy; perhaps those produced by the former were a little greater, 

 as is to be expected from the slightly greater iodine (and therefore 

 presumably thyroxin) content. 



The thyroid feeding was commenced in different experiments at 

 from the 30th to the 34th day of age, continued for 18 or 19 days, and 

 then bread and milk alone were given for from 18 to 48 days. At 

 the conclusion of each experiment the animals were chloroformed, 

 dissected as rapidly as possible, and the organs transferred to stoppered 

 glass vessels and weighed. 



During the experiments 7 animals died, one control female, 

 and 3 males and 3 females during thyroid feeding. Most of the 

 latter showed evidence of tetany. Three animals developed tetany 

 but recovered. 



Details of Experiments 



Experiment 1. A litter of seven rats, two males and five females, born March 

 9th, 1921. One of each sex was used as control. Thyroid feeding was commenced 

 on the 33rd day of age, and at the rate of 1:5000 of body-weight (preparation B), 

 for rats 1, 6 and 7. Rat 4 was fed thyroxin for 8 days and subsequently thyroid; 

 it is omitted from the record. Rat 5 was fed thyroid at the ratio of 1:2000. On 

 the 9th day of treatment, at 3.45 p.m., this rat developed typical tetany, with 

 rapid breathing, dragging of hind limbs, and flexion of fore-limbs. An injection 

 of 0.5 per cent. CaCh was given 20 minutes later, but the shock of injection brought 

 on a marked and typical paroxysm, with very rapid breathing and tetanic spasms. 

 The animal died 3 minutes later. Post-mortem examination of the heart showed 

 the ventricles in systole and auricles very distended. The pupils were not con- 

 tracted. The remaining animals were fed thyroid daily for 19 daj'S, and then a 

 normal diet for the succeeding 27 days. 



Experiment 2. A litter of 6 rats, 4 males and 2 females, born September 10th. 

 One of each sex was used as control. Thyroid feeding (1:5000; preparation A) was 

 commenced on the 34th day of age, and continued for 18 days; subsequent normal 

 feeding was given for 48 days. Rat 2 was found dead on the morning of the 7th 



