THE CARDIAC IMPULSE. 



35 



fluid, the exit of which is hindered by the aortic pressure. If the blood 

 be shut off from the heart, then a finger placed on the ventricle is 

 forced out on systole to a far less extent than before. An outward 

 thrust is still perceptible, however, and this must be so, for muscle 

 layers compress other muscle layers. Thus the columnar carneae and 

 papillary muscles are forced together. In this case, it is the elastic 

 resilience of the compressed muscle whicli produces the impulse. 



The points to be remembered in regard to the origin of the impulse 

 are these 



1. The impulse is synchronous with the commencement of the 

 period of rising intraventricular tension. 



2. The impulse occurs where the ventricular wall touches the 

 parietes of the chest. 



3. By no locomotion of the whole heart can its origin be entirely 

 explained, for it persists after the suppression of the auricular con- 

 traction, and of the recoil due to the output. 



4. The primary factor is the hardening of the muscular mass, the 

 secondary factor the erection of the ventricles upon the base of the heart. 



5. The impulse is felt at a different spot in each position of the 

 body, owing to the influence of gravity acting on the heart. 



Cardiographs. The impulse of the heart can be recorded by various 

 forms of apparatus. In animals a receiving tambour has been inserted between 

 the chest wall and the heart, and placed in connection with a recording 

 tambour. 1 In obtaining 

 curves from man, the 

 receiving instrument has 

 necessarily to be applied 

 to the external wall of 

 the thorax over the seat 

 of impulse. Probably the 

 best form of cardiograph 

 is that of Edgren, which is 

 a modification of Marey's 

 instrument. 2 



In this instrument 

 the receiving tambour 

 (c) is placed within an 

 outer rigid chamber (A B), 

 which is fastened to the 

 thorax by elastic bands 

 (/<?), which encircle the 

 chest. The pressure of 

 the button (K) of the tam- 

 bour on the seat of im- 

 pulse can be varied by a 



toothed wheel and rod (Ji\ 



,, . . . v h FIG. 23. Edgren s cardiograph. 



while small spiral springs 



(i) placed between the roof of the tambour and the rubber membrane 

 give to the latter the requisite amount of tension. The tube (d) passes to 

 the recording instrument, and the tube (e) enables the observer to listen to 

 the sounds of the heart, at the same time that the impulse is recorded. 

 By this apparatus the movements of the chest wall are excluded, for the 

 whole apparatus moves with the thorax. Only the cardiac impulse affects 



1 Chauveau and Marey, Mem. Acad. de mtd., Paris, 1863, tome xxvi. p. 284. 



2 Skandin. Arch. f. Physiol, Leipzig, 1889-1891, Bd. i. S. 74. 



