302 Dr. R. McCarrison, Effects of Fat Excess on the 



iodine ; and those in whose presence food-assimilation was not favoured by 

 iodine. The first category is further divisible into two sub-classes, according 

 to the degree of the favouring influence of iodine on assimilation : those in 

 which the retarded rate of growth induced by the fat was wholly or almost 

 wholly compensated for by 1"0 mgrm. of iodine per gramme of food-mixture ; 

 and those in which the retarded rate of growth was favourably influenced, 

 but not compensated for, by this dosage of iodine. In the first sub-class are 

 included butter, lard and oleic acid (figs. 2 and 3); in the second, cocoa-nut 

 oil and arachis oil. 



B. Ohservations on Ifetamorphosis. 



(1) Among tadpoles which received metallic iodine in the proportion of 

 one part of iodine to 100 parts of food-mixture, but no pond weed, the 

 following results were observed at the end of thirty days of experiment : — 



(a) Tadpoles whose food-mixture contained butter showed well-developed 



hind limbs in every case ; the stage of metamorphosis was in advance 

 of controls which received the same amount of iodine but no fats, 

 and was far in advance of those which received other fats. Butter 

 thus hastened the abnormal metamorphosis induced by a large iodine 

 intake. 



(b) A similar but less uniform result was observed with regard to cocoa-nut 



oil. This oil hastened in certain individuals the normal meta- 

 morphosis induced by a large iodine intake. 



(c) Oleic acid and linseed oil exercised little or no influence on the 



abnormally rapid metamorphosis induced by a high iodine intake. 



(d) Cod-liver oil, on the other hand, markedly delayed the abnormally 



rapid metamorphosis induced by a high iodine intake, and at the 

 same time the loss of weight induced by the iodine was less pro- 

 nounced than in the case of other fats, oleic acid excepted. 



It was observed that the hind limbs developing in the course 'of this 

 experiment were unhealthy looking and sometimes shrivelled, especially in 

 the case of linseed oil, 



(2) Among tadpoles which received 0'5 to 1 mgrm. of iodine per gram of 

 food-mixture and pond weed, the rate of metamorphosis was little affected in 

 the absence of fats ; the larger dose of iodine tended to hasten metamorphosis 

 slightly. When, however, fats were present, it was observed that meta- 

 morphosis was markedly delayed by the fluid fats, and to a much less 

 extent by the harder fats ; and, that while iodine tended to compensate for 

 the delay in metamorphosis induced by oleic acid and arachis oil, no such 



