ACTION OF THE TECTORIAL MEMBRANE 499 



instead of having a single arm extending from the periphery of 

 the membrane to its center as shown in figure 5. The planes 

 of the two ends were cut at right angles to its long axis instead 

 of in the form shown in figure 7. It was of interest to find that 

 the vibrations of the tympanic membrane were transferred to 

 the fluid in the model better and more definitely by the arrange- 

 ment of a single arm extending from the periphery to the middle 

 of the tympanic membrane, similar to the arrangement of the 

 manubrium of the malleus in the mammalian ear, than by the 

 straight piece pressing across the center of the membrane and 

 extending at right angles to both its surface and that of the fen- 

 estra vestibuli. The form found most efficient was somewhat 

 similar to the columella of birds. 



Sound producers of various types were tried, including pipes 

 giving different tones, trumpets (a cornet and a trombone), 

 horns of different kinds, and finally an assortment of ordinary 

 brass organ reeds. Organ reeds were used chiefly in the work 

 for two reasons: first, instruments producing sound waves by 

 means of vibrating tongues seemed to act upon the apparatus 

 more definitely than any of those tried which gave in other ways 

 the alternate phases of condensation and rarefaction, and second, 

 the vibration frequency of each of the organ reeds was known, 

 the name of the note it produced being stamped upon it. With 

 the other instruments, the vibration frequency of a given sound 

 had to be previously determined by means of a standard tuning 

 fork and the kymograph, used with a writing arm registering the 

 vibrations of the tympanic membrane. The form of the brass 

 organ reed used is shown in figure 5, B. In order that its vi- 

 brations could be conducted directly into the external auditory 

 meatus, a wooden box or horn (H, fig. 5, A) was constructed into 

 the end of which fitted a removable cover for the reed (RC). 

 This cover was so constructed that reeds could be interchanged 

 at will. Air was blown through the reed by way of the rubber 

 tube (RT). The whole sound producing apparatus was held 

 in place by a heavy, ordinary filter stand and no part of it was 

 allowed to touch the model nor the table upon which the model 

 sat. The end of the horn was inserted into the large end of the 



