636 



PHYSIOLOGY OF RESPIRATION. 



condition of the center. The two results which are most constantly 

 obtained and which may therefore be especially emphasized are as 

 follows: first, with weak stimuli the inspiratory movements are in- 

 hibited partially or completely, giving either smaller movements or, 

 in a condition of narcosis, complete cessation of respirations, with 



Fig. 257. To show the effect of section of the vagi on the respiratory movements 

 (rabbit). The right vagus was cut at x and caused a slight augmentation and slowing 

 of the movements. The left vagus was cut at xx and caused first a short inhibition (due 

 to mechanical stimulation) which was then followed by the typical slow and deep respi- 

 rations seen under these conditions. (Dawson.) 



the thorax in the stage of passive expiration (Fig. 256), or, second, 

 the rate of the inspiratory movements may be increased and this 

 may end finally in an inspiratory standstill, that is, the respiratory 

 movements cease with the chest in an inspiratory position (Fig. 258), 



Fig. 258. To illustrate the inspiratory effect from stimulation of the central end of 

 the vagus. The downstroke represents inspiration; the upstroke, expiration. During- 

 the period of stimulation the respirations are increased in frequency and the chest remains 

 in a condition of inspiration. (Lewandowsky .) 



the inspiratory muscles being in a condition of tetanic contraction. 

 When both the inspiratory and expiratory muscles are considered, 

 the variety of effects that may be obtained from stimulation of the 

 afferent fibers of the vagus is perplexing, especially with strong 



