5(j ON THE FUNCTIONS OF THE HEART AND ARTERIES. 



about fifteen to sixteen. The tension will also become one 

 eighth greater, and the force of the lieart must be capable 

 of supporting a column of one hundrtd and one inches. 

 This force would, however, requiie to be somewhat in- 

 creased, from the consideration, that the force required at 

 the end of any canal, during the reflection of a pulsation 

 or wave of any kind, is twice as great as the force exerted 

 during its transmission ; and the force employed in the ori- 

 gination of a wave or pulse in a quiescent fluid is the same 

 as is required for its reflection ; on the other hand, a weaker 

 pulsation, proceeding into a narrower channel, becomes 

 more energetic, so that, from this consideration, a force 

 somewhat smaller would be required in the heart : on the 

 ■whole, however, it appears probable, that the former of 

 these corrections must be the more considerable, and that 

 the force of the heart must be measured by the pressure of 

 a column rather more than less than one hundred and one 

 inches high : nor would this force by any means require a 

 strong exertion of muscular power ; for it only implies a 

 tension of something less than thr^e pounds for each inch 

 of the circumference of the greatest section of the heart; 

 and supposing the mean thickness half an inch, an equal 

 number of the fibres of some other muscles of the body 

 would be capable of exerting a force of more than two hun- 

 dred pounds, jn the state of the j^reatest possible action. 

 The force The force, here assigned t© each pulsation, agrees ex- 



agrces with an tremely well with the inference, that may be drawn from an 

 Ihaes""^" ^ experiment of Hales, on the ascent of the blood in a tube 

 connected with an artery of a horse. The whole height of 

 the column being nine feet, the blood rope about three 

 inches higher during each pulsation, which was repeated 

 fifty or sixty times in a minute : now we may suppose the 

 acceleration to liave extended a little beyond the first half 

 of the sp;'.ce thus described, so that two inches were de- 

 scribed in two fifths of a second ; and if there had been no 

 friction, nor any other cause of relardation, there can be no 

 doubt, that at least four inches would have been described 

 in the same time; but the same column of nine feet, if it 

 had been actuated by its own weight, would have described 

 thirty one inches in the same time: consequently the force, 



with 



