HABIT FORMAT lOX IX FROGS 321 



strength of the shock was determined by applying the electrode 

 holding the food to the hind leg of another frog; a shock that was 

 just strong enough to cause a reaction was then used on the me- 

 dium-sized Rana clamata. But the electric shock turned out to be 

 very much stronger in the mouth of the Rana clamata than on the 

 hind leg of the test frog. The moment the frog snapped up 

 the cockroach which had been placed into the cage, the frog 

 immediately executed a series of wild hops until the roach 

 was got rid of. The speed of the reactions prevented me from 

 observing how the roach was brought out. Whether the frog 

 actively threw it out, or whether it was pulled out by the elas- 

 ticity of the copper electrode, I do not know. Other roaches 

 were offered with and without electrode, but none were noticed. 



Tenth day. Roaches, earthworms, and mealworms were 

 placed into the cage at various times of the day, but the frog 

 became interested in none of them. 



Eleventh, twelfth and thirteenth days. No reactions toward 

 any sort of food were observed. 



Fourteenth day. One mealworm was eaten one minute after 

 presentation. 



Fifteenth to twentieth days. From one to three mealworms 

 were eaten each day. No earthworms were eaten or even 

 noticed. 



The experiment with the electric stimulus has little value. 

 The stimulus was unfortunately much too strong. This put 

 the frog into a state similar to that produced by fear, and in 

 consequence the eating instinct was wholh' inhibited for a few 

 days. It is of interest, however, to note that discrimination 

 between mealworms and earthw^orms was not interfered with 

 to an appreciable extent, excepting perhaps that discrimination 

 was sharpened. 



At the same time that the medium-sized spring frog was ex- 

 jjerimented on with mealworms and with earthworms chemically 

 treated, a large male Rana clamata was also fed with an irregular 

 succession of these organisms to determine whether the rapidity 

 of habit formation varied markedly among different individuals 

 of the species. 



First day. (On account of the generally negative character 

 of the results the mealworms which were fed are not recorded. 

 From two to six mealworms were eaten each day.) An earth- 



