324 PHYSIOLOGY CHAP. 



the effect being usually manifested only after a heart-beat (Schiff, 

 Pfliiger and others), as shown in Figs. 144, 145, 146. 



Excitation by a single induction shock has little effect ; 

 constant currents usually produce retardation only ; tetanising 

 induction currents are the most effective (Donders, Heidenhain, 

 etc.). 



Stronger currents produce a more obvious and prolonged in- 

 hibition : minimal currents always produce delay, never accelera- 

 tion of rhythm, contrary to the observations of Moleschott (v. 

 Bezold, Pfliiger, Eosenthal, etc.). The frequency of the induction 



FIG. Uti. Depressor effect of moderate excitation of frog's \agus. (Tigerstedt.) The two vertical 

 lines indicate the duration of .stimulation. Carotid connected with Ludwig's kymograph. 



shock tells more than intensity of the stimulus (Legros and 

 Onimus). 



A difference in the inhibitory action of the two vagi has often 

 been observed, particularly in amphibia (Meyer, Gaskell, Mac- 

 William, Wesley Mills, Tarchanoff). In the rabbit the right 

 vagus is often more effective than the left (Masoin). The same 

 has been found in the horse and dog (Arloing and Tripier), and 

 also in man (Czermak). 



When on cessation of the arrest produced by the stimulation 

 of one vagus the other is at once excited, an effect similar to the 

 first is produced, without any resting period, if the first nerve had 

 not been unduly fatigued (Tarchanoff, Eckhard, MacWilliam and 

 others). 



