Growth and Metamorphosis of Tadpoles. 



303 



tendency to compensation occurred in the presence of linseed oil and cod- 

 liver oil. 



Summary of Results. 



(1) An excess in the food of tadpoles of the several fats used caused great 



retardation in the rate of grov?th. 



(2) Iodine in amounts of 5 to 1"0 mgrm. of food-mixture tended to 



compensate for the retardation of growth induced by butter, lard, 

 oleic acid, cocoa-nut oil, and arachis oil, but not for that induced by 

 linseed oil and cod-liver oil. 



(3) The normal rate of metamorphosis was but slightly affected by the 



harder fats : butter, cocoa-nut oil, and lard ; but was delayed by the 

 fluid and less saturated fats : oleic acid, arachis oil, linseed oil, and 

 cod-liver oil. 



(4) The delayed rate of normal metamorphosis induced by the fluid fats 



tended to be compensated for by the presence of small quantities of 

 iodine in the food in the case of oleic acid and arachis oil, but was 

 not compensated for by the same quantities of iodine in the case 

 of linseed oil and cod-liver oil. 



(5) The abnormal metamorphosis induced by a high iodine intake was 



considerably hastened by a high proportion of butter in the food- 

 mixture, and to a lesser degree by a high proportion of cocoa-nut oil 

 in the food-mixture, but was markedly retarded by a similar propor- 

 tion of cod-liver oil in the food-mixture. 

 Conclusion. — It seems probable from these results that, in so far as certain 

 fats — butter, lard, oleic acid, cocoa-nut oil, and arachis oil — are- 

 concerned, an iodine intake, proportionate to their intake in the food, 

 is requisite for the maintenance of normal metabolism. The influence 

 of cod-liver oil and of linseed oil in further retarding growth in the 

 presence of an amount of iodine, that is favourable to growth in 

 the case of other fats, is as yet not understood. 

 The histological findings in connection with the thyroid gland will form 

 the subject of a further communication. 



