500 APPENDIX 



up the heart, pass the moistened thread under the bulbus arteriosus 

 (coming from the ventricle) and around over the two superior venae 

 cavae, carefully avoiding the inclusion of the aorta. Tie the thread 

 around the junction of the sinus venosus and the right auricle. Draw 

 the ligature with a surgeon's hitch just tightly enough directly over the 

 whitish "crescent." The auricles and ventricles after a movement or 

 two will stop beating, although the sinus-venosus continues. Touch 

 the apex gently with the needle and observe that the ventricles may be 

 easily artificially stimulated to contract. 



(B) The Second Ligature. With the first ligature in place, tie a second 

 bit of moist thread around the heart in the auriculo-ventricular groove 

 just above the ventricle. When properly adjusted just over Bidder's 

 ganglion (which must be found by chance more or less in these small 

 hearts) , the heart begins again its automatic rhythmic beat, but at a rate 

 slower than normal. 



These two experiments, first performed by Stannius in 1851, are more 

 easily carried out successfully than certainly explained. The cause of 

 the phenomena of the first ligature is especially obscure, but there are 

 two tentative explanations: The first ligature may stimulate the inhibi- 

 tory action of Remak's ganglia in connection with the vagus. Another 

 way of accounting for the facts of the first ligature is that, if the beat 

 of the heart originates, as is generally admitted, in the sensitive tissues 

 of the sinus venosus, this ligature may cut off the progress of the impulse, 

 thus making necessary a long pause before the ventricle can gather 

 energy enough to make a beat of its own originating. It is usually con- 

 sidered that the second ligature starts up the heart by stimulating Bidder's 

 ganglion in the auriculo-ventricular septum, and that this constant 

 stimulation has the same (trophic?) influence on the ventricle as has the 

 normal influence coming to this ganglion. 



Expt. 62. Every Contraction Maximal. (" All or None.") (Appara- 

 tus: Kymograph, inductorium, heart-lever, needle, and thread.) Place 

 about under the bulbus venosus of a frog's heart the first ligature of 

 Stannius, as described in the former part of the previous experiment, 

 bringing thereby the heart to a stand-still. Put the pan of the cardio- 

 graph (heart-lever) under the heart without detaching the latter from its 

 anatomical connections, and connect with it wires from the secondary 

 coil of the inductorium arranged for single make and break shocks. 

 Place the secondary coil so far from the primary that neither make nor 

 break causes the apex (ventricle) to contract. Arrange the lever of the 

 cardiograph for writing on the drum while the latter is stationary. 

 Move the secondary coil very slowly and gradually toward the primary 

 until a single break shock causes contraction of the apex. Turn the 

 drum a millimeter by hand and stimulate again with a make-shock. 

 Now gradually increase the strength of the stimulus and make a record 

 each time (allowing at least thirty seconds to elapse between each two) 

 until the shocks are of maximal strength. Comparing the height of 

 the cardiograms, it will be seen that the last is not longer than the first. 



