FORCE OF THE HEART. 197 



was sudden and powerful in its character. The abrupt de- 

 scent of the lever showed that the relaxation was almost in- 

 stantaneous. 



4. The impulse of the hea,rt, as marked by the third lever, 

 was shown to be absolutely synchronous with the ventricular 

 systole. 1 



Condensing the general results obtained by Marey, which 

 are of course subject to a certain amount of variation, we 

 have, dividing the action of the heart into ten equal parts, 

 three distinct periods, which occur in the following order : 



Auricular Systole. -This occupies two- tenths of the heart's 

 action. It is feeble compared with the ventricular systole, 

 and relaxation immediately follows the contraction. 



Ventricular Systole. This occupies four- tenths of the 

 heart's action. The contraction is powerful, and the relaxa- 

 tion sudden. It is absolutely synchronous with the impulse 

 of the heart. 



Diastole. This occupies four-tenths of the heart's action. 



Force of the Heart. There are few points in physiology 

 on which opinions have been more widely divergent, than on 

 the question of the force employed by the heart at each con- 

 traction. Borelli, who was the first to give a definite esti- 

 mate of this force, put it at 180,000 pounds; while the calcu- 

 lations of Keill give only 5 ounces. 3 These estimates, how- 

 ever, were made on purely theoretical grounds. Borelli esti- 

 mated the force employed by the deltoid in sustaining a given 

 weight held at arm's length, and formed his estimate of the 



1 MAKEY, op. cit., p. 6S et seq. I have preferred to give the general signifi- 

 cance of the three traces obtained by Marey, rather than reproduce the traces 

 themselves, which present certain minor characters which might confuse the read- 

 er. Nothing could be more distinct than the illustration of the particular points 

 above enumerated ; and there can be no other opinion than that these observa- 

 tions settle the question of the rhythm of the heart's action in the animals on 

 which the experiments were performed. 



2 JAMES KEILL, M.D., Essays on Several Parts of the Animal (Economy, Lon- 

 don, 1717, pp. 87, 91. 



