EXPERIMENTS ON THE LAKYNX. 637 



rose to heights varying from 54 to 140 mm. of mercuiy, or from 

 about 28 to 72^ inches of water. 



In tlie cat the resistance to the exit of air from the larynx 

 presented by the true vocal cords alone is very small, generally 

 about 6 mm. of mercury. 



When their approximation is aided by a lateral pressure 

 of 100 grammes, a resistance of 16 mm. of mercury may be 

 reached. 



The ventricular bands in the cat are thin and easily coap- 

 tated, but they are not calculated to resist much pressure unless 

 they are supported : such support is afforded by the epiglottis, 

 if it is slightly pressed backwards, and the gentle lateral pressure 

 is made so as to coaptate the cords. 



If firm pressure is applied in this way the resistance pre- 

 sented to the exit of air by the ventricular bands is very con- 

 siderable, and they may not yield even under pressure of from 

 24 to 40 mm. of mercury. To reach the latter figure, however, 

 considerable support from the base of the epiglottis and from 

 the lateral aspects of the larynx is required. When the true 

 cords are approximated, as well as the ventricular bands in the 

 cat, the epiglottis being at the same time slightly depressed and 

 gentle lateral pressure exerted, they easily resist a pressure of 

 30 mm. of mercury, or more. 



The resistance to the ingress of air afforded by the true cords 

 alone, in the cat is very considerable ; when a lateral pressure 

 of 20 grammes is exerted so as to bring them together they 

 easily resist a suction power of 50 or 60 mm. of mercury, and 

 when the lateral pressure is increased they will resist consider- 

 ably greater suction than this. 



The ventricular bands when ordinarily approximated will not 

 resist more than 2 or 3 mm. of mercury. 



In such experiments as these there is not a little difficulty in 

 approximating the vocal cords so as to imitate their closure 

 during life. The lateral pressure exerted, the position of the 

 epiglottis in regard to the cords, the freshness of the larynx, 

 and many other circumstances modify the results obtained to a 

 very considerable extent. By way of example we may mention 

 that m eight measurements of the resistance offered by the 



