ELECTRO-CARDIOGRAM 



807 



active state from the base to the apex. The rate of propagation 

 on the rabbit's ventricle varies from i to 3 metres a second, accord- 

 ing to the rate of the heart-beat. Such observations have been inter- 

 preted as indicating that the excitation, with its accompanying 

 electrical change, begins at the base, then develops in the region of 

 the apex, and finally involves the poition of the ventricles near the 

 aorta and pulmonary artery, possibly extending even into the roots 

 of these vessels. The full explanation of this seemingly erratic 

 course of the excitation wave is doubtless dependent upon a full 

 knowledge of the course and connections of the conducting system, 



ill! 



Pig 298. Electrometer Record from Tortoise Heart (Gotch). One contact upon 

 the sinus, the other on the apex of the ventricle. One complete beat shown. 

 Upward movement signifies relative negativity of the sinus contact. The dark 

 line A shows the auricular effect, and the dark line V the ventricular effect. 

 Time-trace at top, one-fifth second. 



and this we do not possess as yet. The fact that the ventricle is 

 originally developed from a tube with a venous and an arterial end, 

 and that this tube later on becomes bent upon itself so that the two 

 ends (the auricular or venous and the aortic or arterial) lie together 

 at the base of the ventricle, probably affords the clue. It should 

 be mentioned, however, that this explanation of the second rise of 

 the ventricular curve (the T-wave, according to Einthoven's nomen- 

 clature, Fig. 304) is by no means universally accepted. Einthoven, 

 who has worked with the string galvanometer, believes that be- 

 tween the first (R) and the second (T) ventricular waves the whole 

 of the ventricle is in contraction, and that there is no difference of 



