Vocal Cords in Quiet Respiration in Man, 8fc. 421 



respiration in man. It will at once be seen that it is necessary to 

 define this point very clearly, because, as already mentioned before, 

 this part of the investigation is beset with very considerable diffi- 

 culties. 



Whilst, np to this point, the main part of our argument has been 

 based on physiological observations on the human subject, and clinical 

 facts and experiments on animals were only used as corroborative 

 evidence, in this part of our enquiry we have to depend exclusively 

 upon the two last-named factors, and for various reasons neither of 

 them gives us so distinct a reply to the question at issue as would be 

 desirable. 



First, with regard to experiments on animals. 



It has already been stated in a previous chapter that the conditions 

 resulting from section of the laryngeal motor nerves in animals vary 

 very considerably according to species, age, aud individual peculiari- 

 ties of the animals experimented upon, and that, practically, the only 

 point on which a complete consensus of opinion has been obtained 

 consists in the fact that narrowing of the glottis has been described 

 by all observers. To what degree, however, this narrowing interferes 

 with the respiratory functions of the animal operated upon is a 

 question the replies to which vary very considerably. 



The importance of the difference of species and of ages of the 

 animals experimented upon for the decision of this point did not 

 escape the acute observer who first thoroughly studied the influence 

 of the division of the recurrent laryngeal nerves upon life, viz., 

 Legallois. Having observed that in very young dogs the division of 

 these two nerves led to speedy death by asphyxia, he wished to know 

 whether the same phenomena were present* in other specimens of 

 animals. He therefore cut, he tells us,* sometimes the pneumogastric, 

 sometimes the recurrent laryngeal, nerves in cats, rabbits, and guinea- 

 pigs, in the first days of their existence. He found that " cats died in 

 the same manner, and perhaps even more quickly than dogs ; that in 

 guinea-pigs and in rabbits, section of the recurrents' obstructs the 

 glottis less completely, the former only die in about an hour's time, 

 and the rabbits after a half hour." 



Having thus stated the differences in degree depending upon the 

 species of the animals, Legallois proceeded towards determining the 

 influence of age upon the phenomena resulting from sudden diminu- 

 tion of the calibre of the glottis. He found that " section of the 

 recurrent nerves produces a less considerable suffocation in inverse 

 proportion to the age of /he animals ; thus, in dogs and cats about 

 two to three weeks old, this operation still causes dyspnoea, which, 

 though less strong than in the first days after birth, yet is strong 

 enough to cause the death of the animals after a few hours. At the 

 * ' Experiences sur le Principe de la Vie,' 1812, pp. 190, et seq. 



