CIRCULATION OF THE BLOOD 119 



tension. But the arteries, in spite of its pressure, and un- 

 der the force and impulse of the heart, send on the blood 

 from the internal parts of the body to the parts beyond the 

 ligature. And herein consists the difference between the 

 tight and the medium ligature, that the former not only 

 prevents the passage of the blood in the veins, but in the 

 arteries also ; the latter, however, whilst it does not prevent 

 the force of the pulse from extending beyond it, and so 

 propelling the blood to the extremities of the body, com- 

 presses the veins, and greatly or altogether impedes the 

 return of the blood through them. 



Seeing, therefore, that the moderately tight ligature ren- 

 ders the veins turgid and distended, and the whole hand full 

 of blood, I ask, whence is this? Does the blood accumulate 

 below the ligature coming through the veins, or through the 

 arteries, or passing by certain hidden porosities? Through 

 the veins it cannot come; still less can it come through in- 

 visible channels; it must needs, then, arrive by the arteries, 

 in conformity with all that has been already said. That it 

 cannot flow in by the veins appears plainly enough from the 

 fact that the blood cannot be forced towards the heart un- 

 less the ligature be removed; when this is done suddenly all 

 the veins collapse, and disgorge themselves of their contents 

 into the superior parts, the hand at the same time resumes 

 its natural pale colour, the tumefaction and the stagnating 

 blood having disappeared. 



Moreover, he whose arm or wrist has thus been bound for 

 some little time with the medium bandage, so that it has not 

 only got swollen and livid but cold, when the fillet is un- 

 done is aware of something cold making its way upwards 

 along with the returning blood, and reaching the elbow or 

 the axilla. And I have myself been inclined to think that 

 this cold blood rising upwards to the heart was the cause of 

 the fainting that often occurs after blood-letting: fainting 

 frequently supervenes even in robust subjects, and mostly at 

 the moment of undoing the fillet, as the vulgar say, from 

 the turning of the blood. 



Farther, when we see the veins below the ligature in- 

 stantly swell up and become gorged, when from extreme 

 tightness it is somewhat relaxed, the arteries meantime con- 



