210 PHYSIOLOGY CHAP. 



the spheno-salpingo-staphyline muscle or tensor velo-palati is 

 inserted into the hook. 



The lumen is generally closed by the apposition of the mucous 

 membrane, aided by secretion, at the narrowest part of the 

 cartilaginous portion. It is only during certain muscular acts, 

 particularly in swallowing and yawning, that the lumen is dilated 

 by the contraction of the tensor palati, which separates the mem- 

 branous walls of the cartilaginous canal. In some individuals 

 the canal seems to offer very little resistance to opening or to 

 be incompletely closed. In these exceptional cases it is possible 

 on carefully observing the membrana tympani with the otoscope 

 to detect slight movements that coincide with the respiratory 

 rhythm. 



According to some aurists this permanent opening of the tube 

 may be artificially induced by scooping it out with a thin flexible 

 sound to a point beyond the isthmus of the canal, that is, the 

 narrowest portion. The effect of this is to diminish the apprecia- 

 tion of deep tones, as also occurs after slight perforations of the 

 tympanic membrane. This shows that the normal closure of the 

 tube, which hinders the air from escaping through it from the 

 tympanic cavity, creates a condition favourable to the transmission 

 to the labyrinth of the vibrations of the tympanic apparatus due 

 to the sound-waves. 



That the tube is normally closed is clearly proved by the 

 feeling of painful tension which is experienced in the tympanum 

 on climbing into high regions where the air is rarefied, and which 

 is relieved by occasional swallowing. The same sensation is 

 produced when the tympanic membrane is driven inwards by a 

 high atmospheric pressure, such as may be obtained in a pneumatic 

 chamber. In this case, too, the unpleasant feeling of tension 

 ceases when by swallowing, or by Valsalva's experiment, the 

 lumen of the canal is rendered pervious for a moment, so that 

 the pressure of the air in the tympanum becomes equal to that of 

 the atmosphere. 



Valsalva's experiment consists in making a strong expiration 

 after closing the mouth and nostrils, so that air is forced through 

 the tube. Besides this so-called positive experiment of Valsalva 

 there is also the negative experiment of Toynbee, i.e. a deep 

 inspiration with the nostrils and mouth closed, so that air is 

 aspirated out of the cavity. At the moment of aspirating the 

 tympanic air an endotic murmur, due to the stretching of the 

 tympanic membrane towards the interior of the cavity, is pro- 

 duced. When pharyngeal catarrh spreads along the tube, it 

 causes permanent occlusion of the canal with dulness of hearing 

 and an unpleasant sense of tension in the ear, due to the absorp- 

 tion and rarefaction of the air in the cavity, and the consequent 

 ex vacuo tension of the tympanic apparatus. Efforts to relieve 



