332 RESPIRATION 



branch adapted for measuring the variations of pressure during respira- 

 tion. Connect the free limb of the tracheal tube with an ether apparatus 

 and adjust to secure constant anesthesia. Connect the side branch of the 

 tracheal tube with a Marey's recording tambour of medium size and sup- 

 plied with a comparatively delicate membrane. The amplitude of the 

 movements of the tambour may be regulated by a screw compress on a 

 connecting tube. Arrange an induction coil with platinum electrodes in 

 the usual manner for stimulating by means of the interrupted current. 

 Record the results of the experiment along with the variations of blood- 

 pressure on a continuous-paper kymograph; the instrument should be 

 supplied with a time signal, a stimulating signal, etc. 



Now stimulate the skin of the abdominal region, the groin, with a com- 

 paratively strong medium induction current, figure 2466. Dissect out the 

 sciatic nerve, cut it, stimulate the central end with a mild to medium 

 strength of current. The stimulus should be graduated carefully, for 

 there is often such a great increase in respiratory rate and volume that the 

 animal may become overanesthetized. 



b. The Effect of Stimulating the Vagus Nerve. Isolate and stimulate 

 the vagus nerve with a medium strength of stimulus. The effect is usually 

 complete inhibition of respiratory movements. By means of graduated 

 stimuli one may demonstrate the accelerator effects from the stimulation 

 of the vagus. Stimulate also the superior laryngeal, and compare with the 

 effects of stimulating the whole vagus. 



c. The Effect of Cutting the Vagus Nerves. Isolate both vagus nerves 

 and section them as nearly at the same moment as possible. Be sure to 

 mark on the tracing the exact moment at which the nerves are cut. This 

 experiment should be performed with every accessory condition as con- 

 stant as possible, and the animal should not be disturbed for one or two 

 minutes so that the effects of the section will be recorded, figure 240. The 

 result is always a marked deepening and slowing of the respiratory 

 movements. 



d. The Effect of Stimulating the Central End of the Vagus. Upon stimu- 

 lating the central end of the vagus after section, the respiration rate will be 

 inhibited as in b, showing that the vagus nerves carry afferent respiratory 

 fibers, figure 241. 



e. The Effect of Stimulation of the Phrenic Nerves. Isolate the right 

 phrenic nerve at its origin from the brachial plexus and stimulate it with a 

 medium strength of stimulus. Upon stimulating the nerve the diaphragm 

 will remain in contraction and the record will show that the thorax is in the 

 inspiratory phase. The phrenic is therefore a simple motor nerve. 



Section this nerve and note the change in the character of respiratory 

 movements; make direct observations on the diaphragm, examining from 

 the abdominal side. 



