164 LYMPHATIC SYSTEM 



the movement of the heart in living pigs and he explained how 

 the aorta led from the heart and branched and ramified through 

 all parts of the body. Sometime later, Vesalius attacked one of 

 Galen's beliefs by doubting the existence of pores in the partition 

 in the center of the heart. But people were still under the influ- 

 ence of traditional teaching, and would not willingly discard too 

 much of that which had been previously taught. In his dissec- 

 tions, Vesalius had noted the parallel arrangement of the arteries 

 and veins, but he still did not observe that the blood moved in a 

 circuit. Another investigator, Cesalpino, in 1571, ventured the 

 opinion that some of the blood left the heart through arteries and 

 returned by the veins. He seems to have reasoned this out with- 

 out experimentation. In 1616, Harvey stated that he not only 

 failed to find pores in the heart through which blood passed 

 from one side to the other, but that the partition of the heart 

 was unusually solid and compact. He examined the heart 

 action of some forty diflPerent animals and described the pulsa- 

 tions. He examined the circulatory system of a dead man 

 by making an injection of warm water from the pulmonary 

 artery through the lungs into the left ventricle. He finally 

 concluded as a result of his observations and experimentations 

 that the blood moves in a circuit, and that the beating of the 

 heart supplies the propelling force. Although he understood that 

 the blood moved in a '^ kind of circle," he did not know about the 

 capillary network connecting the arteries and veins. Malpighi, in 

 1660, was the first to observe, with the aid of lenses, that the blood 

 moved through the capillaries from the arteries to the veins. 



Harvey's work was the result of reasoning based on the obser- 

 vations of the structure and pulsations of the heart. He explained 

 how the contraction of the heart forced blood into the arteries and 

 how this movement produced the pulse. He pointed out that 

 the amount of blood which left the left ventricle of the heart in a 

 given time must return and be sent out again, because, in a half 



