1032 
Dfi,. W. H. GASKELL ON THE RHYTHM OF THE HEART OF 
the passage of a contraction wave to the ventricle, and not because it weakens a 
nervous impulse from the sinus to the ventricle. 
Again, when by section of the auricle of the Tortoise only every second contraction 
passes the block and induces a contraction of the ventricle, stimulation of the vagus 
is able to cause every contraction to pass, in a manner similar to that observed in the 
case of the Frog when the clamp was tightened. This, then, would seem to show that 
m this latter case too the vagus produced this effect, not so much by its influence upon 
the excitability of the ventricular muscle as by its power to remove the blocking of 
the auricular contractions caused by the pressure of the clamp upon the auricular 
fibres at their termination in the auriculo-ventricular groove. 
Lastly, I find that with a section of the auricular muscle, such that every contrac¬ 
tion is able to pass at a certain rhythm, only every second contraction passes at a 
quicker rhythm ; i.e., the time required for the auricular tissue to recover itself after 
a contraction is much longer at the blocking point than at other parts of the auricle. 
In this way many cases of half-rhythm which are coincident with an increased rapidity 
of rhythm are to be explained. 
Description of Figures. 
In all the figures the divisions on the line traced by the time marker correspond to 
intervals of two seconds. The duration of the vagus stimulation is in all cases marked 
by two thin vertical lines. All the curves read from left to right. 
‘ PLATES 66-70. 
Fig. 1. March 17, 1881. Frog. Auricles and sinus alone heated between the two 
vertical lines. 
Fig. 2. March 28, 1881. Toad. Ventricle alone heated between the two vertical 
lines. 
Fig. 3. June 17, 1881. Frog. Clamp in auriculo-ventricular groove tightened at the 
place denoted by the arrow. 
Fig. 4. Feb. 16, 1881. Frog. Stimulation of vagus. Sec. coil at 13 centime. No 
clamp. Ventricular beats only registered. 
Fig. 5. March 17, 1881. Frog. Stimulation of vagus. Sec. coil at 10 centims. 
Auricles and sinus were heated. In consequence, auricles are beating very 
rapidly, and ventricle does not respond to every auricular beat. 
Fig. 6. March 15, 1881. Frog. Stimulation of vagus. Sec. coil at 8 centims. The 
stimulation was probably weaker for some reason in curve A than in curve B. 
Fig. 7. March 8, 1881. Frog. Stimulation of vagus. Sec. coil at 10 centims. The 
auricular contractions are just visible during the ventricular standstill. 
Fig. 8. June 23, 1881. Toad. Stimulation of vagus. Sec. coil at 10 centims. 
