174 CIRCULATION OF THE BLOOD 



While the heart is filling during diastole, the curve rises gradually above 

 the abscissa ; but while the ventricles are being emptied, i. e., while the semi- 

 lunar valves are opened, the pressure against the breast wall is somewhat less 

 and the recording tambour cannot therefore follow the progressive increase of 

 blood pressure. 



For the graphic registration of the apex beat in man the method of air 

 transmission is generally used, as for example with the apparatus represented 



in Fig. 61 (cardiograph of Marey). A me- 

 tallic box bears the plunger, p, fastened 

 into two small metallic disks, between which 

 the rubber membrane of the tambour is 

 placed. A spiral spring between the inner 

 of these disks and the bottom of the box gives 

 a suitable tension to the membrane. The 

 cardiograph is placed over the thoracic wall 

 in such a manner that the plunger presses on 

 the area of the apex beat. The side tube, r, 

 leading out of the box places it in connection 

 with the recording tambour. 

 FIG. 61. Receiving tambour of It is evident that an apparatus placed 



Marey's cardiograph. over the chest wall in this manner must give 



a curve which agrees essentially with the one 



obtained by means of a balloon inserted between the heart and chest wall ; for the 

 movements of the chest wall, which is now between the tambour and the heart, 

 are determined by the movements of the heart. 



The human cardiograms published in the literature show considerable 

 differences in form, depending primarily upon the nature of the recording 

 apparatus employed. From what we know of the possibilities of this apparatus 

 (Hiirthle) we may say that the form of the normal cardiogram of man is 

 about that represented in Fig. 62. We have here, as in the animals, an ascend- 

 ing limb, a plateau, which inclines toward the abscissa or runs parallel to it, 

 and a descending limb. Besides there are some small elevations, which in part 

 at least are artifacts. 



Often, if not always, the cardiogram begins with a small elevation which 

 is caused by the contraction of the auricle. After this follows the steep rise 

 caused by the contraction of the ventricle. In this case the beginning of the 

 ventricular contraction can be clearly recognized. It may happen however 

 that the auricular contraction is not specially marked, but passes uninter- 

 ruptedly into the ascent produced by the ventricular contraction, in which 

 case it would be erroneous to reckon the latter from the foot of the ascending 

 limb. This form of the curve results often from too little tension of the 

 cardiograph. 



On the cardiogram one sometimes finds at the end of the auricular systole 

 the above-mentioned (page 170) elevation, called by Chauveau the intersy 'stole, 

 which indicates the moment of closure of the atrio-ventricular valves. As a rule, 

 however, the elevation does not occur on the human cardiogram. On the other 

 hand, the moment of opening of the semilunar valves in some cases comes out 

 clearly at the first turning point of the cardiogram, where the ascending limb 

 passes over into the plateau (Fig. 62, b}. The time interval between the base 

 and the first turning point of the cardiogram, therefore, represents the period 



