Utilization of Food Substances. 109 



at a temperature lower by 10 degrees, needed at the same rate of 

 growth 243 days to metamorphose. K was therefore higher than 

 for series A (51). The same was true for other series of marbled 

 as well as tiger salamanders; in all of these series the length of 

 the larval period was increased more than the rate of growth was 

 decreased, and consequently the product K increased. In short, 

 during the same amount of growth less of the substance was 

 produced at low temperature than at high temperature, though 

 the same kind of food was given to all the larvae. 



If one diminishes the quantity of food instead of lowering the 

 temperature, the rate of growth decreases as in the case of lowered 

 temperature, and the length of the larval period increases, as is 

 shown in the record of four series of marbled salamanders. All 

 four series were kept at the same temperature and fed the same 

 kind of food, but Series D received only one half, Series E only 

 one quarter the amount of food which was given to Series C, and A 

 received still less food. Consequently, as in lowered temperature, 

 the rate of growth was decreased with the diminution of food, 

 and the length of the larval period was increased. But while in 

 lower temperature the length of the larval period was increased 

 more than the rate of growth was decreased, hunger increased 

 the length of the larval period less than it decreased the rate of 

 growth, and consequently K decreased instead of increasing as in 

 lowered temperature. 



When the same kind of food is available to the amphibian 

 organism, a certain substance required for metamorphosis is 

 elaborated, at the same rate of growth, the more easily the less 

 food there is available, and the less readily the more the tempera- 

 ture is lowered. 



