84 PARKER— A CRITICAL SURVEY OF 



the surrounding medium. Such disturbances, as has long been 

 known, may stimulate the organs of touch as well as the ear. 

 Kreidl, therefore, rightly maintained that these disturbances must 

 be shown to stimulate the ear before they can be said to be stimuli 

 for hearing. Lee (1898, p. 138) has also emphasized the impor- 

 tance of regarding hearing "in the sense in which the term is ordi- 

 narily used." It seems, therefore, fair to conclude that any dis- 

 turbance that can be said to produce hearing through the human 

 ear may also be said to call forth hearing in a fish provided it can 

 be shown to act through the ear and not simply through the skin or 

 other such receptive surface. 



The human ear is normally stimulated by a great variety of 

 sounds, some in the nature of tones and others in the nature of 

 noises. We hear not only the tones of a tuning-fork, but the less 

 pure tones of musical instruments, and of the voice as well as an 

 immense array of very irregular disturbances, difficult to describe 

 from a physical standpoint and classed generally as noises. Perhaps 

 among the most extreme of these are explosive noises such as are 

 produced by the clapping of hands, the discharge of firearms and 

 so forth. All of these we certainly hear, for they affect us chiefly 

 through the ear and their inefficiency as stimuli for the deaf is well 

 known. 



When they are extreme, they produce what we commonly speak 

 of as shock or concussion and there has been a tendency on the part 

 of some workers (Bateson, 1890, p. 252) to regard the shock as 

 distinct from the sound. From a physical standppint there seems 

 to be no grounds for this assured distinction. The powerful dis- 

 turbance that emanates from the midst of an explosion is not made 

 up of sound and shock or concussion, but is a single complex dis- 

 turbance which when it strikes our bodies may stimulate ears, skin, 

 and even other sense organs. In so far as it affects our ears, how- 

 ever, we must admit it as a stimulus for hearing. Kreidl (1895, p. 

 459) has pointed out that sounds with shock quality are more effec- 

 tive as stimuli for fishes than ordinary tones are, and the experi- 

 mental work of later investigators goes far to substantiate this con- 

 clusion. Nevertheless, for reasons already given, this state of 



