THE MECHANISM OF THE HEART PUMP 1019 



pressure in animals or the heart sounds in man. This cardiogram 

 presents considerable similarities to the endocardiac pressure curve ; 

 in both there is an ascending limb, a plateau, and a descending 

 limb, and in many cases a small elevation occurs at the begin- 



FIG. 400. A cardiograph. This is strapped round the chest, the central 

 button is applied to the ' apex beat,' and its pressure on the chest wall 

 regulated by means of the three screws at the sides. The tube at the 

 upper part of the instrument serves to connect the drum of the cardio- 

 graph with a registering tambour such as that shown in Fig. 391. 



ning of a curve during the contraction of the auricle. The exact 

 point at which the auricular passes into the ventricular contraction 

 varies from case to case and may be altered by altering the degree of 

 pressure put on the recording button. In the first figure given the 

 auricular systole finishes before the main rise of the lever occurs. In 

 many cases, however, the elevation due to the auricular systole may 

 take up the greater part of the ascending limb of the curve, as in 

 Fig. 402. 



In the experiment from which this figure was taken the heart 



FIG. 401. Cardiogram. (HURTHLE.) 



sounds were recorded at the same time as the apex beat. It will be 

 seen that the first heart sound, corresponding to the ventricular systole, 

 begins, not at the commencement of the rise of the cardiogram, but 

 at the notch near the top of the ascent. The first part of the ascent 

 is therefore caused by the increase in the volume of the ventricle, due 

 to the sudden contraction of the auricles, the ventricular systole being 

 marked by the notch near the top of the curve. Owing to the co-opera- 



