MEMBRA^A TYMPANI. 201 



to certain physiological variations in tension, due to contrac- 

 tion of the tensor tympani. It is also evident that this mem- 

 brane may be drawn in and rendered tense by exhausting or 

 rarefying the air in the drum. If the mouth and nose be 

 closed and we attempt to breathe forcibly by expanding the 

 chest, the external pressure tightens the membrane. In this 

 condition, Dr. "Wollaston has shown that the ear is rendered 

 insensible to grave sounds, but that high-pitched sounds 

 appear to be more intense. If the tension be relieved, as 

 may be done by an act of swallowing, the grave sounds are 

 heard with normal distinctness. This experiment, tried at a 

 concert, produces the curious effect of abolishing a great 

 number of the lowest tones, while the shrill sounds are heard 

 very acutely. 1 The same phenomena are observed when the 

 external pressure is increased by descent in a diving-bell. 11 



Undoubted cases of voluntary contraction of the tensor 

 tympani have been observed by otologists ; and in these, by 

 bringing this muscle into action, the limit of the perception 

 of high tones is greatly increased. In two instances of this 

 kind, recorded by Dr. Blake, of Boston, the ordinary limit 

 of perception was found to be three thousand single vibra- 

 tions ; and, by contraction of the muscle, this was increased 

 to five thousand single vibrations. 8 



The admirable experiments of Savart, to which we have 

 already alluded, show that the membrana tympani vibrates 



1 WOLLASTON, On Sounds inaudible by Certain Ears. Philosophical Transac- 

 tions, London, 1820, p. 306, et seq. 



2 TODD, Cyclopaedia of Anatomy and Physiology ', London, 1836-1839, vol. ii., 

 p. 575, Article, Hearing. 



3 BLAKE, Summary of Results of Experiments on the Perception of High Musical 

 Tones. Trans, of the American Otological Society, Boston, 1872, vol. v., p. 77. 



Other cases of voluntary contraction of the tensor tympani have been ob- 

 served. Schapringer, who possessed this faculty, was able to contract the 

 muscle so as to render all notes below seventy vibrations inaudible, while the 

 higher tones were more readily perceived the more energetic the tension of the 

 membrane. ( Ueber die Contraction des Trommelfelhpanners. Sitzungberichte der 

 kaiserlichen Akademie der Wissenschaften, mathematisch-naturwissenscJiaftliche 

 Classe, Wien, 1870, Bd. Ixii., Zweite Abtheilung, S. 572.) 



