32 UNIVERSITY OF MISSOURI STUDIES 



audible. I remind the reader, however, that we are deriving 

 this conclusion on the basis of our provisional assumptions, 

 and further, that we are speaking here of movements of the 

 stirrup, not of rhythmical pressure changes of the air in the 

 external ear or of movements of a tuning fork or any other 

 vibrating body. In discussing later the effect of the latter 

 conditions upon the stirrup, we shall see that their form is 

 not necessarily identical with the form of the stirrup move- 

 ment. 



As yet, we have studied only very simple movements of 

 the stirrup. Before we take up the problem of how the inner 



ear analyzes more complicated move- 

 The physiological ments of the stirrup, we ought to remem- 

 condition of ber that we have not yet discussed the 



tone intensity physiological condition of tone intensity. 



We have spoken only of the frequency 

 with which shocks are received by the nerve ends. But the 

 frequency of the shocks determines only the attributes of 

 pitch and quality, not the attribute of intensity of a tone sen- 

 sation. Let us look to another sense organ, the olfactory 

 organ, for a suggestion. On what physiological condition 

 does the intensity of an odor depend? Although we have no 

 definite knowledge here any more than in the sense of hear- 

 ing, we have reason to believe that the intensity of an odor 

 depends, or may depend, on two conditions: 1. The num- 

 ber of nerve ends stimulated; and 2. the concentration of the 

 substance which stimulates each of these nerve ends. Ac- 

 cepting this suggestion we have to see what conditions might 

 determine tone intensity. Only these two can come up for 

 consideration, so far as I can see : 1. The number of nerve 

 ends which receive shocks in a definite frequency; and 2. 

 the suddenness, the impetuosity with which each nerve end 

 is shaken when the point of the partition in which it is lo- 

 cated is jerked down. Now, the second of these two conditions 



