58 CIRCULATION OF THE BLOOD 



heart will become of a much paler colour than before, 

 even when in its state of dilatation. It also becomes 

 smaller, because it is no longer filled with blood which 

 normally reaches it from the vena cava. At last it begins 

 to beat more slowly, so that it seems as if it were about 

 to die. If, however, the impediment to the flow of blood 

 is removed, the colour and size of the heart are instantly 

 restored. 



" But if the artery instead of the vein is compressed, 

 you will observe the part between the obstacle and the 

 heart, and the heart itself, to become inordinately dis- 

 tended, to assume a deep purple or even livid colour. 

 At length it is so much oppressed with blood that you will 

 believe it about to be choked. When, however, the 

 obstacle is removed, all things immediately return to their 

 natural state in colour, size, and impulse." 



14. " Now make an experiment on the arm of a man, 

 using a bandage as employed in blood-letting. The best 

 subject is a lean man who has large veins. . . . Let the 

 bandage be tied round the arm and drawn as tightly as 

 can be borne. It will first be perceived that beyond the 

 bandage, neither in the wrist nor elsewhere, do the 

 arteries pulsate. Immediately above the bandage, how- 

 ever, the artery rises higher at each expansion and throbs 

 more violently ... as if it strove to break through the 

 obstacle to its current. . . . The hand retains its natural 

 colour and appearance, though in the course of time it 

 begins to get somewhat colder." 



" After the bandage has been kept thus for some time, 

 loosen it a little. . . . The whole hand and arm will now 

 instantly become deeply coloured and distended, and the 

 veins themselves tumid and knotted. After ten or twelve 

 pulses the hand will be excessively distended, injected, 

 gorged with blood. . . ." 



" Now apply the finger attentively over the artery 



