456 J. F. GUDERNATSCH 



Experiment V 



Rana temporaria, Set VIII to XI, voluntarily mixed. These hatched 

 April 10 to 13 and the experiment started May 8, 1912. 



In addition to the organs used in the previous experiments, 

 pancreas and testicle were given as food in this experiment. 

 Each organ was given in two forms; with one group of tadpoles 

 a small piece of the tissue was placed in the water; to a second 

 group the food was given in a crushed form, a piece of the tissue 

 being squeezed between the fingers, until it was broken into 

 minute particles. This was done for two reasons. First to al- 

 low juices that might form an active part of the glands to ooze 

 out into the water as quickly as possible, second to give the 

 weaker individuals a chance to find food particles. In almost 

 every experiment it was seen that a number of the smallest in- 

 dividuals did not grow and after a time began to die. It seems, 

 however, that this is not due to an inability to obtain food, but 

 because they were less fit to live and were simply weeded out in 

 the early stages of development. 



The tadpoles fed on the crushed glands developed in essentially 

 the same manner as the others, thus after several weeks both 

 sets were placed in one dish and fed alike. 



One set of animals was fed on clotted blood. They did best 

 of all. A control set was fed on Elodea canadensis and another 

 w^as starved. 



All of the tadpoles were about 4 weeks old at the beginning 

 of the experiment and had not been fed. When starved the ani- 

 mals eat the dead ones, if these are not removed, but their rate 

 of growth can by no means compare with that of tadpoles re- 

 ceiving plenty of food. 



The thyroid-fed tadpoles showed the same rapid development 

 as observed in previous experiments. They could not be kept 

 alive longer than 23 days, although after 10 days they were put 

 in water through which a constant current of air was passed. 

 The groups fed on other tissues also showed the usual rate of 

 growth. Those individuals fed on spleen, liver and thymus ran 

 rather parallel courses and progressed somewhat faster during the 



