THE NERVOUS REGULATION OF RESPIRATION 537 



In addition, the procedure of double vagotomy, as the division of 

 both vagi nerves is called, invariably leads to other conditions which 

 are absolutely incompatible with normal function. 



Dogs are somewhat more resistant and frequently survive this 

 operation for many days, and in some instances even for an indefinite 

 period of time, whereas rabbits, sheep and horses succumb to it in the 

 course of a few days. In addition to the effects upon respiration 

 and the action of the heart, these animals also exhibit difficulties 

 in deglutition, digestion and assimilation. They lose weight constantly 

 until their lungs eventually consolidate in consequence of a pneumonic 

 affection. Whether, this infiltration of the pulmonary tissue is caused 

 by trophic influences or by the ingress of food and bacteria, owing 

 to the -functional uselessness of the epiglottis, has not been definitely 

 ascertained. 



The division of these nerves should really be effected by the method 

 of freezing rather than by that of cutting, because by this means their 

 power of conduction may be destroyed without the usual initial 

 period of excitation.^ This accounts for the fact that the diminution 

 in the respiratory activity is commonly initiated by a hyperpneic type 

 of respiration. Furthermore, it should be remembered that these 

 alterations in the frequency and depth of the respiratory movements 

 manifest themselves only if both nerves are cut and that the division 

 of only one nerve generally produces little or no change. Aside from 

 the motor effects evoked with the aid of the inferior laryngeal nerve, 

 the stimulation of the distal end of the divided vagus leaves the general 

 character of the respiratory movements unchanged. It should be 

 noted, however, that this nerve also contains efferent fibers for the 

 musculature of the bronchi (Fig. 263). This has been shown by Roy 

 and Brown, 2 as well as by Einthoven,^ who have found that the excita- 

 tion of either vagus produces a constriction of the bronchi of both 

 lungs, while the division of either nerve eventually evokes a dilatation 

 of these tubes on the side of the section. It may readily be surmised 

 that these changes in the size of the bronchial passage must lead to 

 variations in the volume of the air contained therein. In this con- 

 nection it should also be mentioned that the recurrent attacks of 

 dyspnea, characterizing spasmodic asthma, are believed to be as- 

 sociated with spasms of the bronchial musculature. These are said 

 to find their origin in a neuritic condition of the vagus nerve. 



The excitation of the central end of the divided vagus nerve with 

 a quickly interrupted current may be followed by either a slowing or a 

 quickening of the respiratory movements. The precise character of the 

 effect produced by this procedure depends upon the strength of the 

 stimulus and the irritabihty of the respiratory mechanisna.^ To 



1 Gad, Archiv fur Anat. und Physiol., 1880, 9. 



2 Jour, of Physiol., vi, 1885, 21. 



3 Pfluger's Archiv, ci, 1892, 367. 



4 Rosenthal, Archiv fiir Anat. und Physiol., 1881, 39. 



