564 THE HUMAN BODY. 



hair process, d. The remaining cells, rod cells, ~b, are in 

 several rows: each has a slender inner process extending to 

 the basement membrane and an outer which reaches to the 

 bases of the columnar cells and appears there to end in a 

 rigid membrane, e, which is perforated for the passage of the 

 hairs. They probably are mere supporting structures an- 

 swering somewhat to the fibres of Miiller of the retina. 

 After death the hairs tend to break up into a bunch of fila- 

 ments, and they are found imbedded in a sticky mucus-like 

 material, which is probably a post-mortem product: it has 

 been named the cupula terminalis. In some parts of the 

 utricle and saccule is a region of epithelium very similar to 

 that above described, and also supplied with nerve-fibres. In 

 connection with them are found minute calcareous particles, 

 otoliths or ear-stories. 



The Loudness, Pitch, and Timbre of Sounds. Sounds, 

 as sensations, fall into two groups notes and noises. Physi- 

 cally, sounds consist of vibrations, and these, under most 

 circumstances, when they first reach our auditory organs, are 

 alternating rarefactions and condensations of the air, or 

 aerial waves. When the waves follow one another uni- 

 formly, or periodically, the resulting sensation (if any) is a 

 note; when the vibrations are aperiodic it is a noise. In 

 notes we recognize (1) loudness or intensity; (2) pitch; (3) 

 quality or timbre, or, as it has been called, tone color; a note 

 of a given loudness and pitch produced by a flute and by a 

 violin has a different character or individuality in each case; 

 this quality is its timbre. Before understanding the work- 

 ing of the auditory mechanism we must get some idea of the 

 physical qualities in objective sound of which the subjective 

 differences of auditory sensations are signs. 



The loudness of a sound depends on the force of the aerial 

 waves ; the greater the intensity of the alternating condensa- 

 tions and rarefactions of these in the external auditory 

 meatus, the louder the sound. The pitch of a note depends 

 on the length of the waves, that is the distance from one 

 point of greatest condensation to the next, or (what amounts 

 to the same thing) on the number of waves reaching the ear 

 in given time, say a second. The shorter the waves the 

 more rapidly they follow one another, and the higher the 

 pitch of the note. When audible vibrations bear the ratio 

 1:2 to one another, we hear the musical interval called an 



