300 Dr. K. McCarrison. Effects of Fat Excess on the 



to modify greatly the rate of growth of tadpoles — were, as far as possible, 

 uniform. In the case of the lard and arachis oil dishes, the animals had the 

 advantage of more heat from the sun, as these dishes were placed on a bench 

 near a sunny window. In general, however, the factor of variations in 

 external temperature was not responsible to any appreciable degree for 

 variations in the rates of growth or metamorphosis. The room temperature 

 during the course of the experiments ranged between 65° and 70° F. 



(12) The mortality was negligible during the first three weeks of the 

 experiment ; later, and especially after the fortieth day, it was considerable 

 amongst tadpoles receiving fluid fats, much less so amongst those receiving 

 the solid fats. The presence of iodine in the food-mixtures tended to reduce 

 the death rate in tadpoles receiving fluid fats. OEdema was a frequent 

 cause of death in certain dishes : controls, cod-liver oil, arachis oil and lard. 

 It appeared to have no relation to the presence or absence of iodine. 

 Cannibalism, so usual among tadpoles, was conspicuous by its almost total 

 absence, a circumstance which demonstrates the complete nature of the food 

 provided. 



(13) Pigmentation varied greatly in different dishes : the most pigmented 

 were in general the smaller individuals and those receiving the fluid fats; 

 the least pigmented were in general the larger individuals and those receiving 

 the solid fats. Tadpoles receiving butter were, on the whole, less pigmented 

 than those receiving other fats, although exceptions to this generalisation 

 occurred among tadpoles receiving food-mixtures containing the more solid 

 fats. It seems not improbable that the various fats may have had different 

 effects on the pineal body. 



(14) Individual variation in size was a very notable feature in the case of 

 tadpoles receiving oleic acid, whether with or without iodine. It was a 

 noticeable feature also in controls receiving no fats, and in those receiving 

 food-mixtures containing lard, cocoa-nut oil and butter. Little or no variation 

 in size was found among tadpoles receiving food-mixtures containing arachis- 

 oil, linseed oil and cod-liver oil. 



(15) The method of recording rates of growth was as follows : The tadpoles 

 were weighed weekly. At the first two weekly weighings only twenty from 

 each dish were weighed. Subsequently — and as variations in the rate of 

 growth of different individuals became more obvious — all were weighed. 

 They were removed from their dishes into a gauze net. The wet mass of 

 tadpoles at the bottom of the net was then freed of adherent water by 

 means of absorbent paper, and the mass turned into a known weight of 

 water. The total weight was thus arrived at, and the weight of twenty was 

 calculated therefrom for purposes of charting. This figure was selected so as- 



