Vocal Cords in Quiet Respiration in Man, fyc. 411 



In man : 22 : 30 = a : x. 

 In woman : 22 : 28 = a : x. 



30a 

 Whence it follows that in men : x is equal to -777- or = a 1'36. In 



28a 

 women: x = -^ = 1'27. 



It is obvious that in spite of all these precautions no absolutely 

 correct numbers can be obtained, because, on the one hand, the dis- 

 tance of the observer's eye, even if he be emmetropic, is not always 

 exactly equal to 22 cm. from the centre of the mirror, and, on the 

 other, the distances of the level of the glottis from the centre of the 

 mirror as given above for men and women are only average figures, 

 from which the exact figures in individual cases might not incon- 

 siderably differ. Still I have found by measuring in a double manner 

 a large number of dead larynges in order to control my laryngoscopic 

 measurements (viz., by first examining them with the graduated 

 mirror, whilst the conditions of life were as carefully as possible 

 imitated so far as position, distances, .&c., are concerned, and by 

 afterwards introducing a fine compass into the larynx, and measuring 

 directly the distances between the inner surfaces of the arytenoid 

 cartilages), that with sufficient practice nearly accurate results are 

 obtained by direct measurements. The maximum error committed 

 in measuring laryngoscopically was 1 mm., the average \ mm., 

 while in a large number of cases the laryngoscopic and direct 

 measurements completely corresponded with one another. 



Of the measurements of dead larynges, it has already been stated 



Thus if A = 22 

 and B = 8 



A + B = 30 = the distance (if the person examined be an adult man). 



22 



The ratio of size of scale to the object will then be = = 0'733 ; i.e., 0'733 mm. 



on the mirror scale correspond to 1 mm. real size. 



If the eye be removed to a small extent further from the mirror, say to 24 cm, 

 instead of 22 cm., the result will not be very different, as both the numerator and 

 denominator will be increased. In the first case, as before stated, 



fj- 0-733. 



In the latter 



24 



The real size (x) will then be'to the apparent (a) = 1 : 0'733, or x = Q./TQQ* 

 This gives the real width of the glottis in adult men. 



In women x = . 



0-75 



I am much obliged to Mr. Stevenson for having given me this formula. 



2 F 2 



