258 PHYSIOLOGY CHAP. 



For the vowel u (oo) = booty. 



6 (or) = order. 



(ol) = dollar. 

 a (ah) = father. 

 e (a) = lazy. 



e (e) = letter. 



1 (ee) = feeling. 



Taking this scale as the measure of auditory acuteness, the words are 

 audible at a progressively increasing distance in young people with normal 

 hearing. According to Gradenigo the lesser distance for low sounds is more 

 pronounced when the external and middle ear are affected than under normal 

 conditions ; in diseases of the labyrinth, on the contrary, audition of the 

 higher sounds appears most defective. 



Besides the human voice other sounds are used for testing audition, e.g. 

 the ticking of a watch, or better Politzer's apparatus, consisting of a hammer 

 which always drops from the same height upon a steel cylinder. 



To test the perception of musical tones it is necessary to employ a series 

 of tuning-forks, like that of Bezold and Edelmann, which extend from 12 

 to 870 double vibrations ; for higher sounds an accurately graduated Galton's 

 whistle, which can give 50,000 double vibrations, is 

 now used almost exclusively. 



In testing auditory acuity (acumetry) tuning-forks are 

 used, and made to vibrate as far as possible at uniform 

 intensity, while the time is measured during which the 

 gradually diminishing sound is still perceptible. In 

 practice this method encounters certain clifficulties, owing 

 particularly to the difficulty of determining time -relations 

 in the decrement of tone. To obviate this difficulty 

 Gradenigo (1899) proposed a new, easier and more exact 

 method in order to obtain experimental proof of the 

 diminution of sound from the tuning-fork. Starting from 

 'pieces 'of black "paper the fact that the intensity of a tone is directly pro- 

 which can be applied portional to the amplitude of vibration, he made the 

 tuning 6 -fo?k! n vibrations of one of the prongs of the fork which gave 



40-60, at any rate less than iOO, simple vibrations per 

 second, visible to the eye, by fixing to its free end a triangular, elongated, 

 black figure with sharp edges cut out of cardboard, bearing three or 

 more divisional marks on one side (Fig. 104). Clearly, when the tuning-fork 

 vibrates, the cardboard tongue must vibrate also, and produce a visual 

 image which varies with the amplitude of vibration. At the maximum of 

 amplitude, i.e. when the tone is strongest, two separate figures appear if the 

 amplitude of the vibrations exceeds the breadth of the figure. When, as the 

 tone diminishes, the vibrations become less ample, the two images begin to 

 overlap at the inner side, and it is clear that the less the amplitude of 

 vibration the larger will be the overlapping portion of the two images. The 

 intensity of the tone made perceptible by this experiment is accurately 

 estimated by the greater or lesser portion of the two images, which can 

 easily be measured by the scale at the side of the figure (Fig. 105). 



The note of the tuning-fork can be transmitted through the bone, as 

 well as by the air. In Weber's test the stem of the vibrating instrument 

 is placed on the middle line of the skull ; in normal individuals the sound 

 is then localised in the centre of the head, but if one ear is closed, or the 

 external air-passage of one side blocked by disease, it is referred to this ear, 



Rhine's test consists in the fact that in normal individuals the diminish- 

 ing note of a tuning-fork, held close to the auditory meatus, is perceived for 

 a longer time than if the fork is applied to the mastoid process ; in other 

 words, individuals with sound ears hear tones transmitted through the air 



