80 THE HISTORY OF SCIENCE 



side of the heart, the pulmonary artery inosculates 

 with the pulmonary veins, which convey it to the left 

 side of the heart. This muscular pump drives it into 

 the aorta. It still remains to be shown that in the 

 liinbs the blood passes from the arteries to the veins. 

 Bandage the arm so tightly that no pulse is felt at 

 the wrist. The hand appears at first natural, and 

 then grows cold. Loose the bandage sufficiently to 

 restore the pulse. The hand and forearm become 

 suffused and swollen. In the first place the supply 

 of blood from the deep-lying arteries is cut off. In 

 the second case the blood returning by the superficial 

 veins is dammed back. In the limbs as in the lungs 

 the blood passes from artery to vein by anastomoses 

 and porosities. All these arteries have their source 

 in the aorta ; all these veins pour their stream ulti- 

 mately into the vena cava. The veins have valves, 

 which prevent the blood flowing except toward the 

 heart. Again, the veins and arteries form a connected 

 system ; for through either a vein or an artery all 

 the blood may be drained off. The arguments by 

 which Harvey supported his view were various. The 

 opening clause of his first chapter, " When I first 

 gave my mind to vivisection as a means of discover- 

 ing the motions and uses of the heart," throws a 

 strong light on his special method of experimental 

 investigation. 



Bacon, stimulated by what he called philanthropic 

 always aimed, as we have seen, to establish man's 

 control over nature. But all power of a high order 

 depends on an understanding of the essential char- 

 acter, or law, of heat, light, sound, gravity, and the 

 like. Nothing short of a knowledge of the underly- 



