206 



THE CIRCULATION OF THE BLOOD 



does not materially influence the spread of the conduction wave over 

 the ventricular walls (Lewis) as was once supposed. The Purkinje system 

 furnishes the shorter pathway. These facts have been demonstrated 



0350 



0250 



0120 



0200 



0250 



FIG. 176^. Transection of the dog's heart to show the spread of the conduction 

 stimulus from the bundle to the different parts of the ventricular walls, and the delay 

 in conduction through the walls by muscle paths. (Lewis.) 



by recording the time of arrival of the stimulus at different points 

 on the ventricular wall, figure 176^. The companion figure, 176^, gives 

 a schematic transection of the dog's heart to indicate the direction 



FIG. 177. The rate of different isolated strips of mammalian ventricle under 



the influence of changes of temperature. nodal strip, 



coronary strip, J^ temperature variation, time in minutes. Tempera- 



ture in degrees centigrade, rate in beats per ten seconds. (Moorehouse.) 



of spread of the stimulus from the inner surface into and through the 

 muscle walls of the two ventricles. The delay in sequence between the 

 auricles and ventricles is represented by this rate of conduction through 



