

THE EAR, HEARING, TASTE AND SMELL 193 



rods arc stiff and arranged side by side in two rows, leaned against 

 one another by their upper ends so as to cover in a tunnel; they are 

 known respectively as the inner and outer rods, the former being 

 nearer the lamina spiralis. Each has a somewhat dilated base, 

 firmly fixed to the basilar membrane; an expanded head where it 

 meets its fellow (the inner rod presenting there a concavity into 

 which the rounded head of the outer fits); and a slender shaft 

 uniting the two, slightly curved like an italic/. The inner rods are 

 more slender and more numerous than the outer, the numbers be- 

 ing about 6,000 and 4,500 respectively. Attached to the external 

 sides of the head of the outer rods is the reticular membrane (r, 

 Fig. 74), which is stiff and perforated by holes. External to the 

 outer rods come four rows of outer hair-cells, connected like the 

 inner row with nerve-fibers; their bristles project into the holes of 

 the reticular membrane. Beyond the outer hair-cells is ordinary 

 columnar epithelium, which passes gradually into cuboidal cells 

 lining most of the membranous cochlea. The upper lip of the 

 sulcus spiralis is uncovered by epithelium, and is known as 

 the limbus lamina spiralis; from it projects the tectorial mem- 

 brane (t, Fig. 73) which extends over the rods of Corti and 

 the hair-cells. 



The Loudness, Pitch, and Timbre of Sounds. Sounds, as sensa- 

 tions, fall into two groups notes and noises. Physically, 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 fol- 

 low one another uniformly, 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) qual- 

 ity 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 dif- 

 ferent character or individuality in each case; this quality is its 

 timbre. Before understanding the working of the auditory mech- 

 anism we must get some idea of the physical qualities in ob- 

 jective 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 condensations and rare- 

 factions of these in the external auditory meatus, the louder the 



