^0 ON THE FUNCTIONS OF THE HEART AND ARTERIES, 



that we cannot attribute to the arterial system less than -J- 

 of the whole blood. 



, It raav be supposed that the heart throws out, at each 

 -An ounce and j i i ... 



half thrown pulsation, that is ahout seve ity-Sve times in a minute, an 

 out at each ounce and a half of blood: hence the mean velority in the 

 pulsation oi • , • i i i i ^ • 



the heart. aorta becomes eight uiches and a halt in a second : and the 



\«?locuy from velocity in each of the succeedingj segments must of course 

 8| in. to a 93d •' . , ? . 



ofan inch in a be smaller, in proportion as the joint areas of all the corre- 



secoftd, sponding sections are larger than the area of the aorta : for 



example, in the last order of vessels, of which the diameter 



is the eleven hundredth ofan inch, the velocity will be one 



ninety-third of an inch: and this result agrees sufficiently 



well with Hales's observation of the velocity in the capillary 



arteries of a frog, which was one ninetieth part of an inch 



Hall'er qties- only. It is true that Haller is disposed to question the ac- 



tioiied the ac- curacy of this observation, and to attribute a uiuch greater 



euracv of , . i i i i ^ • i i i -n i 



ilaiej, vel€x;ity to the blood flowuig through the capillary vessels, 



b'Ut he did not attempt either to measure the velocity, or to 

 bnt, hesf>me- determine it by calculation : nor is this the oiily instance in 

 times reasoned which Haller has been led to reason erroneously, from a 

 erioa.ous}, ^^^^^ ^f tnathematical knowledge: he may, however, have 

 observed the particles of blood moving in the axis of a ves- 

 sel with a velocity much exceeding the mean velocity of its 

 EesiRtance whole contents. If we calculate upon these foundations, 



from fnetinn from tile formula which I have already laid before the So- 

 if the blood . . ... , , , • 1 ■ 1 1 ,. - ■• 



vsere water. ciety, it will appear, that the resistance which the friction 



of the arteries would occcasion, if water circulated in them 



instead of b!' « d, with an equal velocity, must amount to a 



force equivalent to the pressure of a column of fifteen inches 



iiu(\ a half: to this we may add about a fonrlh for the re- 



bistance of the capillary veins, and we may estimate the 



whole fricton for water, at twenty inches. The only coii- 



^on^ideraLle part of this force is derived from the terra 



^ Z in the value of f: the term increases for each suc- 



cessive segment in the ratio 1 : 1-49425 zz ] : n, and the 



« 3 ... 1 



sum of the series is to the first term, as to 1. 



V — 1 

 Tlie rcsi tarre ^^ npy'-ears also, that a very pmall portiou«nly of the resist- 

 ^lery little ox- .^^,^.^, jg created in the larger vessels: tlnis as far as the 



twentieth 



