CHAPTER XII 



NATURAL AND PHYSICAL SCIENCE IN THE SEVEN- 

 TEENTH CENTURY 



THE CIRCULATION OF THE BLOOD : HARVEY (1578-1657). The 

 blood has always been regarded as one of the principal parts of 

 the body. Hippocrates considered it one of his four great 

 "humors," and in the Hebrew Scriptures it is stated that "the 

 blood ... is the life." Yet up to the seventeenth century nothing 

 definite was known of its movements throughout the body. That 

 it was under pressure must have been known, for it flowed or 

 "escaped " freely from wounds, and flow results only from pressure 

 of some sort, while escape is relief from detention. The arteries 

 had been misinterpreted for centuries and were early considered to 

 be air tubes, because they were studied only after death when as 

 we now know they are empty. Even the dissections of the anato- 

 mists of the sixteenth century had failed to reveal the complete and 

 true office of the arteries, and it remained for Harvey, an English 

 pupil of the Italian anatomist Fabricius, to make largely 

 through the vivisection of animals and observation of the heart 

 and arteries in actual operation discoveries of basic importance 

 in anatomy, physiology, embryology, and medicine (see Appendix). 



While working in Italy, Harvey learned of and doubtless saw 

 the valves in the veins which were discovered by Fabricius. These 

 valves are thin flaps of tissue so placed as to check the flow of blood 

 in one direction while offering no resistance to that flowing the other 

 way. On his return to England, Harvey apparently pondered on 

 the function of these valves and saw that they could be of use only 

 by permitting the flow of the blood in one direction while prevent- 

 ing its movement in the opposite direction. At this time it was 

 supposed that the blood simply oscillated, or moved back and forth 



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