io8 



Scientific Proceedings (105). 



63 (1523) 



The influence of hunger and temperature upon the utilization of 



food substances. 



By Eduard Uhlenhuth. 



[From the Laboratories of the Rockefeller Institute for Medical 



Research.] 



In the larvae of amphibians when the thyroid glands begin to 

 excrete the thyroid hormone, metamorphosis of the larvae into 

 adult animals takes place. Since larvae with fully developed 

 thyroid glands frequently do not metamorphose, and since in 

 the thyroid gland of the normal larvae, large quantities of "colloid " 

 are present in the follicles for a considerable time before metamor- 

 phosis, it is very probable that the thyroid gland cannot begin to 

 excrete its hormone unless a second factor is present in the larvae. 

 It seems that this factor is elaborated during the process of growth 

 and must be present in a definite quantity in order that the 

 thyroid function may begin. This is shown in two tables in 

 which for several series of the marbled and the tiger salamanders, 

 the age at which metamorphosis took place and the rate of growth 

 were recorded. The greater the rate of growth the shorter the 

 length of the larval period. As a consequence the product of the 

 rate of growth into the duration of the larval period gives a fairly 

 constant value K. The maximum deviations observed can be 

 traced back to certain causes which will be discussed immediately. 



Hence it is evident that metamorphosis not only depends upon 

 the thyroid hormone but also on a second substance, the quantity 

 of which increases in the same ratio as growth. This second 

 substance must be present in a certain quantity in order that 

 metamorphosis can take place. The rate at which it is formed 

 from the same kind of food and for the same rate of growth is 

 distinctly influenced by two factors; by the quantity of food 

 available to the larvae, and by the temperature. 



A series of the marbled salamanders {A 1 91 6) required 186 

 days to metamorphose, when they grew at a rate of 0.21 ; K was 39. 

 Another series (C 191 6), which was fed the same food but kept 



