262 Animal Life and Intelligence. 



and so on) of the fundamental 33. The effects of these 

 on the organ of hearing fuse or combine with the pre- 

 dominant effect of the fundamental tone. In harmonious 

 chords, also, two or more fundamental tones, with their 

 accompaniment of partials, blend in sensation so com- 

 pletely that it requires a keen musical ear and some 

 training to analyze them into their component elements. 



The delicacy of discrimination of tones is greatest in 

 the mid-region of hearing ; and there is much individual 

 variation in accuracy of ear. I have made experiments on 

 many individuals to test their powers in this respect. I 

 found some who were unable, in the mid-region of hearing, 

 to state which was the higher of two notes sounded on a 

 violin, the tones of which were separated by a major third, 

 and in one case by a fifth. With notes on the piano the 

 discrimination was more delicate, and yet more delicate 

 when the notes were sung. In such cases tone-discrimina- 

 tion is deficient ; and between these and the musician, who 

 is stated to be able to distinguish tones separated by only 

 -f of a tone, there are many intermediate stages. 



It is beyond my purpose to describe, in more than a 

 very general way, the nature of the auditory apparatus of 

 man. The vibrations of the air are received by the drum- 

 membrane, which lies in the auditory passage. From this 

 it is transmitted, by a chain of small bones, to the inner 

 auditory apparatus. This consists of two small mem- 

 branous sacs, with one of which three membranous looped 

 tubes, the semicircular canals, are connected; with the 

 other is connected a spiral tube, the cochlear canal. These 

 membranous sacs and canals are filled with fluid, and are 

 surrounded by the fluid which fills the bony cavity in 

 which they lie. This bony cavity has two little windows, 

 one oval and the other round, across each of which a 

 membrane is stretched. The oval membrane is in con- 

 nection with the chain of auditory bones ; and when this 

 is made to vibrate in and out, the membrane of the round 

 window vibrates out and in. Thus the fluid around and 

 within the membranous sacs and canals is set in vibration. 



