On the Interpretation of the Electrocardiogram 
281 
this case distinct. The breadth of the roll of sensitive paper on which 
the photographic record is taken is not sufficient to include the whole of 
deflection B. S does not appear in this curve as a distinct summit below 
the zero line, but there is an interruption on the descent of B. After 
the initial complex the record shows a horizontal stretch near the zero 
line, and terminates in the complex T, which here consists of a downward 
followed by an upward deflection. 
In Fig. 3 the right-hand electrode has been appUed to the auricles of 
an isolated spontaneously beating tortoise heart, and the left-hand electrode 
to the apex of the ventricle. The auricular part of the curve is seen to 
consist of an initial complex followed by a terminal slow deflection. 
In Fig. 4 the right-hand electrode has been applied to the sinus of the 
Fig. 3. 
isolated spontaneously beating heart, and the left-hand electrode to the 
apex of the ventricle. The sinus part of the curve is seen to present an 
initial complex and a terminal slow deflection. The sensitiveness of the 
instrument is in this experiment too great to permit of the ventricular 
variation being recorded on the paper. It has been necessary to increase 
the sensitiveness in order to render the sinus variation evident. The rise 
B of the ventricular variation is seen following the auricular variation. 
In the study of the electrocardiogram it is advisable to isolate one 
chamber of the heart, and I have chiefly directed my attention to the 
curve yielded by the quiescent ventricle when it contracts in response to 
artificial stimulation. The form of stimulus employed has been either a 
break induction shock or the mechanical stimulus of a touch by a glass 
