562 THE NERVOUS SYSTEM. 



recurrent nerve is not generally fatal, and that of both the 

 pneumogastric trunks is not always fatal (J. Reid), and, 

 when it is so, the death ensues slowly. This difference is, 

 probably, because the yielding of the cartilages of the 

 larynx in young animals permits the glottis to be closed 

 by the atmospheric pressure in inspiration, and they are 

 thus quickly suffocated unless tracheotomy be performed 

 (Legallois). In old animals, the rigidity and prominence 

 of the arytenoid cartilages prevent the glottis from being 

 completely closed by the atmospheric pressure ; even when 

 all the muscles are paralyzed, a portion at its posterior 

 part remains open, and through this the animal continues 

 to breathe. Yet the diminution of the orifice for respira- 

 tion may add to the difficulty of maintaining life. 



In the case of slower death, after division of both the 

 pneumogastric nerves, the lungs are commonly found 

 gorged with blood, cedematous, or nearly solid, or with a 

 kind of low pneumonia, and with their bronchial tubes 

 full of frothy bloody fluid and mucus, changes to which, in 

 general, the death may be proximately ascribed. These 

 changes are due, perhaps in part, to the influence which 

 the pneumogastric nerves exercise on the movements of 

 the air-cells and bronchi ; yet, since they are not always 

 produced in one lung when its pneumogastric nerve is 

 divided, they cannot be ascribed wholly to the suspension 

 of organic nervous influence (J. Reid). Rather, they may 

 be ascribed to the hindrance to the passage of blood 

 through the lungs, in consequence of the diminished supply 

 of air and the excess of carbonic acid in the air- 

 cells and in the pulmonary capillaries (see p. 239) ; in 

 part, perhaps, to paralysis of the blood-vessels, leading 

 to congestion ; and in part, also, as the experiments 

 of Traube especially show, they appear due to the 

 passage of food and of the various secretions of the mouth 

 and fauces through the glottis, which, being deprived of 

 its sensibility, is no longer stimulated or closed in con- 



