296 Dr. E,. McCarrison. Effects of Fat Excess on the 



type has received confirmation from the work of E. and M. Mellanby, who 

 have recently* reported identical thyroid changes in puppies to whose food 

 butter had been added. Mellanby has further recorded that not only does 

 butter, and in a lesser degree certain other fats, bring about these changes but 

 they do not arise when the fat used is cod-liver oil. 



The innocuous action of cod-liver oil may possibly have some relation to 

 the iofline-content of this oil, which in crude specimens may reach a concen- 

 tration of 1 in 2,000. It was, therefore, thought desirable to examine, by 

 experimental methods, what the relationship between fat metabolism and 

 iodine intake might be, and the relationship of thyroidal activity to both. 



The present communication is a preliminary account of the observations so 

 far made. It is yet too early to provide an explanation of them, but their 

 record will serve to direct attention to etiological and nutritional problems 

 concerned with what may be called the " fat-iodine-thyroid balance." 



Tadpoles were selected as suitable for the purposes in view by reason of the 

 fact that their rate of growth and of metamorphosis is so sensitive to influence 

 by iodine and thyroid extract. It was thought that this sensitiveness might 

 serve as an index of the changes that are induced in the thyroid gland by an 

 excess of fats. 



Details of Experiments. 



(1) Butter, lard, cocoa-nut oil, oleic acid, linseed oil, cod-liver oil, and 

 arachis oil were chosen as the fats to be tested ; these have a wide range of 

 iodine values. The cod-liver oil was of the crude variety — the so-called 

 " cattle cod-liver oil " — its iodine-content was estimated by Mr. A. A. F. Peel 

 and found to be 0'002 per cent. He also found that the linseed oil contained 

 no iodine. 



(2) The tadpoles were hatched from the same batch of eggs. They were 

 selected so as to be of approximately the same size. The experiments com- 

 menced on the eleventh day of their life. 



(3) Fifty tadpoles were placed in each of the twenty-four dishes required 

 for the experiments. There was one litre of tap-water in each dish. The 

 dishes were arranged in three series of eight each. The water was changed 

 daily, and the dishes thoroughly cleansed. 



(4) A basal diet was provided consisting of flour, eighty-five parts, and 

 caseinogen, fifteen parts. Fresh pond weed was supplied : during the first 

 six weeks it was changed every third day, thereafter daily. This diet con- 

 tained an adequate supply of proximate principles, of vitamins and of 

 vegetable matter. The tadpoles ate it with avidity and their rate of growth 

 was vigorous. They were fed daily. 



* Mellanby, E. and M., 'Proc. Physiol. Soc.,' vols. 7 and 10 (Marcli 12, 1921). 



