422 Dr. F. Semon. On the Position of the 



age of three months or more, dogs are no longer so inconvenienced as 

 to die ; cats are much more so, and as soon as one excites them and 

 forces them to walk they fall down as though they were suffocated." 



Similar conditions obtain in rabbits and guinea-pigs. " The 

 dyspnoea which is caused in their case by division of the recurrent 

 nerves is less grave in proportion to their ages, but it is always more 

 severe in guinea-pigs than in rabbits. For instance, the latter are 

 much less inconvenienced by it at the age of one month than guinea- 

 pigs at the age of five months, which may still perish from it within 

 twenty-four hours." 



"The reason of all these differences," continues Legallois, "is 

 easily understood. It consists in the fact that, in proportion to the 

 capacity of the larynx, the opening of the glottis in animals of the 

 same age is greater in one species than in another, and still greater 

 in the adult than at the moment of birth in those of the same species, 

 as already stated by M. Richerand in the human species.* Or 

 assuming that the form of the glottis, on the whole, is similar in 

 these diverse animals, inasmuch as the areas of the smaller figures are 

 to each other as the squares of the homologous dimensions, it is seen 

 that a narrowing of the same kind of the glottic opening must inter- 

 cept the passage of air in very different degrees." 



And Legalloisf sums up his remarks as follows : " The diminution 

 of the glottic opening varies according to the species, and much 

 more even according to the age in certain species. In dogs, and 

 especially in cats, it is so considerable that these animals are suffo- 

 cated as quickly, or nearly so, as if one had ligatured their trachea. 

 In proportion to the growing up of these animals the danger becomes 

 less pressing, and when they have arrived at a certain age they are 

 only slightly inconvenienced by it (namely, by the diminution of the 

 glottis) ; this, at least, is so in dogs. From this it follows that of all 

 the symptoms which are produced by section of the par vagum, the 

 gravest ones, those that kill most quickly, are in certain cases those 

 which depend upon the larynx. On the whole, whenever the diffi- 

 culty of breathing becomes very severe immediately after this opera- 

 tion, it is very likely that its principal cause is in the larynx ; for 

 instance, the violence with which the dyspnoea declares itself suddenly 

 in horses, even in adult ones, and the promptitude of their death 

 show that in these animals the glottis is considerably narrowed. A 

 large opening made in the trachea furnishes simultaneously both the 

 remedy for and the etiology of all these cases. The chink of the glottis, 

 therefore, is never the same in the living subject as is found in, the 

 cadaver, and the arytenoid cartilages need being supported by their 



* ' Nouveaux Elements de Physiologic,' 2 edit., vol. 11, p. 436. 

 t Ibid., p. 231, et sec^. 



