THE NERVOUS REGULATION OF RESPIRATION 



539 



R.C. 



L.V. (cut) 



To artif resp app. 



fibers of inspiration would not be brought into play during quiet 

 respiration. An activation of the latter, however, would result 

 whenever forced expirations are required to effect a more thorough 

 alveolar ventilation. This mechanism, therefore, insures the perfect 

 regulation of the central discharges so that they develop at perfectly 

 precise intervals, but naturally, it is not concerned with the produc- 

 tion of the automaticity of the center. 



This hypothesis may be tested in a simple way by suddenly 

 inflating or deflating the lungs. The first procedure is called 

 positive ventilation and is invari- 

 ably followed by a relaxation of the 

 diaphragm and a long expiratory 

 pause, whereas the second, or nega- 

 tive ventilation, induces a contrac- 

 tion of this septum. Besides, the 

 existence of inspiratory and expira- 

 tory fibers in the vagus is also made 

 probable by the effects obtained on 

 stimulation of the intact vagus or 

 of its central end; in fact, Griitzner 1 

 and Langendorf 2 have proved that 

 the application of a constant current 

 to the vagus results in an inspiratory 

 arrest when descending, and in an 

 expiratory standstill when ascending. 

 In addition, it might be stated that 

 the collapse of the lungs invariably 

 gives rise to a nerve impulse which 

 ascends the vagus and may be regis- 

 tered by means of the string galvano- 

 meter. Head, 3 moreover, has ascer- 

 tained that the collapse of either lung produces much more decided 

 inspiratory efforts than the division of both vagi nerves. This he 

 succeeded in showing in the following way : The left vagus of a rabbit 

 having been cut, the corresponding lung was inflated rhythmically 

 by means of a tube inserted in the left bronchus (Fig. 265). The 

 normal action of the right lung was then suddenly interrupted by 

 opening the right pleura. The resulting collapse of this organ incited 

 an immediate tonic contraction of the diaphragm which generally 

 lasted for some time, although the rhythmic inflation of the left organ 

 prevented the occurrence of dyspnea and asphyxia. 



1 Pfliiger's Archiv, cvii, 1894, 98. 



2 Ibid., cix, 1906, 201. 



3 Jour, of Physiol., x, 1889, 1. 



FIG. 265. DIAGRAM TO ILLUSTRATE 

 HEAD'S EXPERIMENT ON THE EFFECT OF 

 COLLAPSE OF THE LUNG. 



R.C, respiratory center; B.V, L.V, right 

 and left vagi. (Starling.) 



