258 PHYSIOLOGY CHAP. 



For the vowel u (oo) booty. 



o (or) = order. 



o (ol) ^dollar. 



,, (i (ah) father. 



J (a) =la/y. 



e (e) --- letter. 



,. i (ee) = feeling. 



Taking thi- .-c,de a- the measure of auditory aculein-.-, the word- are 

 audible at a progressively increasing distance in young people \\ith normal 

 hearing. According to Gradenigo tne h-.-ser distance for Low sounds is more 



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

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

 higher sounds appears nm-i deiecthe. 



I'.e.-ides the human voice other sounds are used for testing audit ion, /-./. 

 t he ticking of a watch, or better 1'olit/er'.- apjiaratus, con.- 1st ing of a hammer 

 which al\\a\s drop- from the same height upon a steel cylinder. 



To test the perception of musical tone- it i- accessary to employ a series 



ol luning-liork.-, like that of lie/old and Kdelmann, which extend from li! 



7<i double vibrations; for higher sounds an accurately graduated (ialton's 



\\hi.-th-, \\hii-h can give 50,uiMj double vibrations, js, 



now used alnio-t e\clu.-i\ ely. 



In te.-ling auditory acuits nn-u nn'trij) tuning-forks are 

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

 intensity, while the time is mea.-ured during which the 

 Ljiadualh diminishing sound i.- still perceptible. In 

 practice this method -encounters certain difficulties, owing 

 particularly to the difficulty of determining time-relations 

 in the decrement of tone. To obviate this difficulty 

 denigo i'l' s '.i'.' pinpo-ed a new, ea.-ier and more exact 

 method iii older to obtain experimental proof of the 

 , _ T .- diminution of sound from the tuning-fork. Starling from 



pieces of black papei the fact that the intensity of a tone i.- directly pro- 

 w-hid, can iir;ii,pii.-,i p,,rtional to the amplitude of vibration, he made the 

 tuning-fork? vil>rat ions of one of the pnmg> of the fork which gave 



pi-Co, at any rale le-s than l"(i, simple \ibrations per 



sec, ind, visible to the eye, by fixing to it.- fiee end a triangular, elongated, 

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

 more divisional marks on one side Fig. I 1 '!;. ( 'learly, when the tuning-fork 

 vibrates, the cardboard longin- mii-l vibrate also, and produce a visual 

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

 amplitude, i.6. when the lone is strongest, two separate figures appear if tin- 

 amplitude of the vibration.- exceeds the breadth of the figure. When, as tin- 

 tone diminishes, the \ibrations become less ample, tin- two images begin to 

 overlap at the. inner side, and it i- dear that the less the amplitude of 

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

 i/itfii.tihi of the tone made perceptible by this experiment is accurately 

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

 easily be mea.-ured by the scale at the .-ide 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. 



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

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

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

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



