62 



THE CARDIOGRAM. 



of the ventricles, and during it the first sound of the heart occurs. Frequently, 



Cardiographs. A, Marey's original form ; B, Marey's improved form ; C, pansphyginograph 

 (Brondgeest) ; D, cardiograph (Burdon-Sanderson) ; E, that of v. Knoll. 



but erroneously, the cardiac impulse has been ascribed to the contraction of the 



ventricles alone. It, 

 however, is due to 

 all those conditions 

 which cause an eleva- 

 tion in the region of 

 the cardiac impulse. 



[Edgren recorded a 

 human cardiogram, and 

 listened at the same time 

 to the heart sounds, re- 

 cording the latter by 

 -p. 7 means of an electric sig- 



~ ,. . , i . *, A i ^ ~ i ^ nal. The curve rises at 



Cardiogram, a-/ ; 1, beginning of 1st, and 2, 2nd sound. a> with the beginning of 



the first sound, i.e., with the contraction of the ventricles, and reaches the abscissa at/ with the 



beginning of the second sound, i.e., when 

 the semi-lunar valves are closed. The 

 relation between a and the points inter- 

 mediate between it and/, and to the pulse- 

 curve of the carotid, is shown in fig. 38. 

 The letters with the dash correspond to 

 the unmarked letters in the cardiogram.] 



The cause of the ventricular 

 impulse has been much discussed. 

 It depends upon the following : 



(1) The base of the heart (auriculo- 

 ventricular groove) represents during 

 diastole a transversely-placed ellipse 

 (fig. 40, L, FG), while during con- 

 traction it has a more circular figure, 





lig. 38. 



The upper curve from the human carotid ; the lower 



a cardiogram taken simultaneously. 



