§1] 



upon the rate of growth 



329 



The mixture was cooked, neutralized, filtered, sterilized, and 

 infected with the flagellates, which had been isolated by means 

 of capillary tubes. Here again growth was supported by 

 simple, definite foods. 



Amphibia. — It is a great leap from Protozoa to vertebrates, 

 but precise feeding experiments are almost lacking in the 

 invertebrate Metazoa. In the present group come the pioneer 

 experiments of Yung ('83). This author fed a number of 

 tadpoles derived from the same batch of eggs upon foods of 

 various kinds in unlimited quantity and under otherwise 

 similar conditions. After forty-two days the size of the tad- 

 poles in' each lot was measured and the following results were 

 obtained : — 



TABLE XXXIII 

 Results of Feeding Tadpoles on Various Substances 



It will be observed that the importance for growth was not 

 proportional to the calorific properties of the respective foods, 

 for the yolk of the hen's egg has about 40% higher fuel value 

 than dry egg albumen or dry flesh. The least growth occurred 

 with a plant food which is relatively rich in carbohydrates, and 

 has some protein and little fat ; the third greatest growth 

 occurred with the yolk, which has more fat than protein ; next 

 comes egg albumen, with more protein than fat ; and, finally, 

 fish and beef flesh, characterized by their high percentage of 

 nitrogenous matter. The tadpole grows fastest on a highly 

 nitrogenous diet. 



