284 AVERS. [Vol. VI. 



mals the cochlear chamber alone has this relation to the auditory- 

 chain of bones ; still, when we consider the high rate of trans- 

 mission of sound waves in liquid, all parts of the ear must 

 receive the stimulus of any given set of sound waves at practi- 

 cally the same time. 



The rate of transmission in water, which is certainly less 

 than that of the endolymph, is five times as great as that in 

 air. 



It has been very generally assumed that when a sound wave 

 strikes the tympanum, with the mechanical consequence that 

 the membrane of the fenestra ovalis is forced in, the membrane 

 closing the scala vestibuli at the fenestra rotunda is forced out- 

 ward, owing to the propagation of the wave motion from one 

 scala, through the helicotrema, into the other. 



In this explanation it is entirely overlooked that the endolym- 

 phatic duct places the ear in communication with the lymph 

 spaces about the brain, and that consequently wave motion, 

 propagated either through the scala vestibuli or tympani, either 

 singly or together, does not necessarily in the first case, and 

 cannot in the second case, be transmitted beyond the helico- 

 trema ; for any pressure increase in the endolymph is at once 

 relieved by the progression of the stress through the endolym- 

 phatic duct into pericerebral lymph spaces. As we ascend from 

 the lower to the higher animals, the blood pressure increases 

 progressively ; and since the ear lies within the tissues of the 

 animal, in fact within a lymph space, and its walls are sufficiently- 

 thin to allow of ready transmission of pressure changes, it fol- 

 lows that the endolymph is always subject to a stream of rhyth-. 

 mically variable pressures, travelling from within outward — 

 which must be overcome by the sensory waves from without.^ 

 I do not refer to the rapid vibrations which occur in the body 

 with every heart-beat and muscular contraction, and which for 

 the most part give rise to veritable sounds to be heard by atten- 

 tion to them, but only to the condition of a varying pressure in 

 the lymph space (which of course is not so great, either in its 

 amount or its variations, as in the arteries or the veins), which 

 must affect the entrance of sound waves from the lighter 

 medium, the air. I find no better explanation of the perfection 

 of the tympanic transmitting apparatus than the physical neces- 



1 See Recapitulation F. 



