516 



APPENDIX 



2 cm.) If the heart beats rapidly, slow it with cold solution. Record 

 the normal beat, and mark off exact ten-second periods, or use a time- 

 marker. After twenty contractions or so, stimulate the sympathetic 

 (already ligated and cut) above the ligature with a weak tetanizing 

 current of induced electricity. Count again the number of beats in ten- 

 second intervals and compute the percentage of the acceleration over the 

 normal rate. 



In the frog the augmentor impulses leave the cord by the third spinal 

 nerves, go by the communicating branch into the third sympathetic 

 ganglion, up the sympathetic chain to the vagal ganglion, and down the 

 trunk of the vagus. 



The ordinary acceleration from stimulation of these nerves is very 

 variable (10 per cent, or several times that), the acceleration being 

 greater when the heart is already beating slowly; it is also influenced by 

 the length of time the stimulation is continued. Excitation of the nerves 

 in both sides at once accelerates no more than stimulation of only one 

 nerve. The speed of the stimulation-wave passing over the heart muscle 

 is increased. (See also Chapter VIII.) 



FIG. 285 



Stimulation of the peripheral stump of the vago-sympathetic in the frog. The stimulus was 

 an alternating induced current fairly strong, and its time-relations are shown by the middle line. 

 Note the gradual acceleration of the rhythm as the inhibitory influence passed away from 

 the heart-muscle. To be read from left to right. Trie time-line is in seconds. 



Expt. 86. Inhibition of Function. (Apparatus: Frog-board, small 

 test-tube, heart lever, inductorium, chronograph, signal, kymograph.) 

 Pith the brain only of a frog and fasten the body, back down, on the frog- 

 board. Expose the heart by the removal of the sternum and draw the 

 forelegs far apart. Push the test-tube down the esophagus to distend 

 the tissues of the region. Carefully remove the muscles lying between 

 the angle of the jaw and the hyoid bone in the median line. Observe 

 the three fine nerves which pass upward from the angle of the jaw be- 

 tween the flat muscles; the lowest of these is the hypoglossal, next is 

 the vagus accompanied by a blood-vessel, and still farther forward is the 

 glosso-pharyngeal. This "vagus" trunk is, of course, really the vago- 

 sympathetic. 



Divide the glosso-pharyngeal branch of the vagus trunk to prevent 

 disturbing contraction of the muscles. Place the heart in the heart- 



