506 APPENDIX 



veins and proceeds quickly over the heart, the connection between the 

 auricles and the ventricle being made not by nerves, but by a few slender 

 fibers of muscle extending from the auricles to the ventricle. The speed 

 of this contraction-impulse (mechanical) is great, but very much less than 

 that of the (electrical) action-current. Indeed, the contraction of the 

 heart, including its brief latent-period, requires so relatively long that not 

 only the heart's action-current passes, but it has time to stimulate a nerve 

 and produce contraction in a skeletal muscle before the heart's contrac- 

 tion occurs. The difficulty of the experiment is due to the trouble of 

 placing the nerve so as to receive well the heart's action-current. A lack 

 of sensitivity in the nerve and muscle used prevents a good result. 



Expt. 70. Polar Inhibition. (Apparatus: Flat electrode, cell, 

 rheocord, commutator, key, fine copper wire). With one rheocord- 

 pole connect the flat electrode and with the other the piece of fine wire. 

 Cut off the upper jaw of a frog and expose the heart. Place the flat brass- 

 electrode in the mouth of the frog and the end of the fine wire on the 

 beating ventricle. Observe closely the heart-tissue under the end of the 

 fine wire, and with the commutator rocked so that the end of the wire is 

 the anode, close and hold the key. During systole it is clear that con- 

 traction does not occur at this point, for the tissue remains red and does 

 not pale like the remainder of the heart. This is the active inhibitory 

 effect. Now shift the rocker of the commutator so that the fine wire- 

 point becomes the cathode, and close the key again. The effect now 

 occurs during diastole: the spot remains pale while the apex relaxes, 

 indicating that the cathodal stimulation inhibits normal relaxation. 



The results of this experiment must be taken at present empirically 

 they cannot be definitely and certainly explained. When a weak current 

 goes through the heart the anodal pole causes' Tnhibition of contraction 

 at that point, while if the cathodal pole be on the heart, concentrated 

 in space, a local inhibition or relaxation occurs. There have been two- 

 theories of explanation of inhibition in general one that it is purely a 

 nervous effect, and the other, more probable, that the influence arises in 

 the muscle or gland directly. On the latter hypothesis the inhibitory 

 influence comes from a cessation of katabolism, activity involving katab- 

 olism as surely as rest gives rise to the anabolic process. The former is 

 usually obvious, but the anabolic process, giving little sign, may be hard to 

 appreciate. Gaskell goes so far as to say that the inhibitory influence 

 probably sets up active anabolism, which thereupon checks katabolism. 

 This is called the trophic theory of inhibition. There is at present, 

 however, no surety that these two opposed processes may not go on 

 simultaneously in a tissue. Inhibition is a subject of great promise 

 to researchers into the basal relationship of the tissues and the nervous 

 system. 



Expt. 71. Tonus. (Apparatus: Kymograph, etc., muscle-lever, 

 tortoise.) Chop off a tortoise's head and saw off the lower part of the 

 shell. Pass a fine wire through the auricle of the tortoise's isolated heart 

 and connect it with the muscle-lever, arranged to write on the slowly 



