Yerkes, The Sense of Hearing m Frogs. 301 



VI. The Relation of the Ear to Reaction to Sound. 



Abundant evidence has now been presented in support of 

 the statement that the frog is stimulated by sound, but the use 

 of the term audition in connection with these reactions has not 

 been justified. If the investigation were dropped at this point 

 the criticism would doubtless be made that the modifications of 

 tactual reactions produced by sounds may be due to stimulation 

 of certain cutaneous sense organs instead of the organs of the 

 ear, and that therefore nothing has been proved concerning 

 hearing in the frog. In anticipation of this objection to the 

 conclusions which have been drawn from the results of experi- 

 mentation check observations were made on frogs whose ears 

 had been operated upon in various ways.^ 



The operations whose effects serve as evidence of the rela- 

 tion of the ear to the responses to sounds which we are now 

 considering were three : (i) Cutting the tympana ; (2) Cutting 

 the columellae as well as the tympana ; (3) Cutting the eighth 

 nerves from the dorsal side." 



Briefly stated, the results of the three operations mention- 

 ed are as follows. 



1. After cutting of the tympana there is no apparent 

 change in the nature of the influence of sounds. The frogs are 

 at times less responsive to stimuli, and as a rule they do not 

 show as marked reactions to either touch or sound as do the 

 normal animals. 



2. Sounds continue to modify tactual reactions after both 

 columellae and tympana are cut. In one case it was noticed 

 that the influence of the sound of a wooden gong was much 

 increased by this operation, whereas there was no marked 

 change in the influence of the sound of the metal gong. There 



^Through the kindness of Mr. J. H. Mason, graduate student in the depart- 

 ment of zoology of Harvard University, I was enabled to make the following 

 tests on frogs which he had operated upon for the purpose of studying the static 

 functions of the labyrinth organs. 



^Postmortem examination in case of attempted cutting of the nerves showed 

 in most cases that the ear or brain had been injured. In only two instances was 

 the operation sufficiently clean to fulfill the requirements of the experiments. 



