ACTION OF THE TECTORIAL MEMBRANE 497 



the water was replaced with fresh at the beginning of each series 

 of trials with the model. Thus since the work extended inter- 

 mittently through a number of months, it is thought that the 

 water used toward the last at least was fairly free of extracts 

 from the wood and other material used in construction. 



Instead of the copper plates employed for contact with the 

 ends of the platinum wires, very small copper cups containing 

 a drop of mercury were at first tried on the ends of the pieces 

 of heavier copper wire. It was found, however, that the move- 

 ments and changes in shape of the drops of mercury due to 

 changes in surface tension when charged and uncharged seemed 

 to render the contacts less definite and delicate and adjustment 

 of the distance through which contact was made much more 

 difficult than with the use of the copper plates. The plates were 

 kept burnished. 



The trough was always filled completely with water. The bent 

 glass tube, ED, figures 5, 6 and 7, was put in the model to repre- 

 sent the endolymphatic duct of the labyrinth. It was considered 

 a precaution for compensation in any changes in pressure pro- 

 duced by vibratory pulsations and by changes in temperature. 

 By means of this tube the filling with water could be completed 

 after the glass plate had been put on and pressed down water- 

 tight. Remaining air bubbles were gotten rid of through a 

 small hole drilled in the glass plate at its apical end, the hole 

 being closed with a plug of rubber. 



The end of the model representing the basal end of the cochlea 

 is shown in figure 7, A. The fenestrae were represented by cut- 

 ting large holes through the wooden end piece and closing these 

 holes with thin skin. To accomplish this cuffs of sheet copper 

 were made to fit the holes and over one end of each of these 

 was stretched and tied a piece of thin raw-hide of the sheep known 

 as 'drum-head skin.' The end of the cufT carrying the skin was 

 driven into the hole till the skin, or membrane, became flush 

 with ihe inner surface of the trough. Driving in thus made the 

 membranes tense. Then melted wax was poured around the 

 cuffs making their insertion water-tight. The fenestra vestib- 

 uli (FV, fig. 7) was made oval in shape and larger than the 



