THE METABOLIC MACHINEMY OF WIMAr.S 



SOS 



Connective 

 tissue... 



Epitlididl. 

 layer 



Muscle, 

 cells 



physiology of arteries and veins by the early scientists. William 

 Harvey (1578-1657) was the first to understand thoroughly the cir- 

 culatory system, but other earlier and 

 contemporary workers were not far 

 behind him. The great artist, Leo- 

 nardo da Vinci (1452-1519), left in 

 manuscript numerous drawings and 

 notes on the heart and other vessels, 

 stating that the aorta "subdivides 

 into as many principal branches as 

 there are principal parts to be nour- 

 ished, branches which continue to 

 ramify ad infinitum.'' Vesalius 

 (1514-1564) in his famous anatomical 

 treatise, Fahrica, first published in 

 1543, expressed doubt as to the exist- 

 ence of the connecting "pores" be- 

 tween the two sides of the heart. 

 This was an attack upon one of the 

 main features of the teachings of 

 Galen, who believed there was "an ebb 

 and flow of blood within both veins 

 and arteries throughout the system." 

 blood and the arteries vitalized blood. 



(130- 



Epithelial 

 Isyer. 



An artery 



A capillary 



Comparison of the walls of an 

 artery, vein, and t-apillary. 



Diagram showing how valves of a vein 

 prevent the back flow of blood. 



The former contained crude 

 Yet neither Vesalius nor Galen 

 -200 A.D.) apparently under- 

 stood the circulatory system. 



William Harvey is rightfully 

 known as the father of physiology 

 for in 1616 he began presenting his 

 views on the circulation of the 

 blood. His book, however, did not 

 appear until 1628. In it we find 

 evidence for the thesis that the 

 heart is the pump,^ that the arteries 

 dilate passively as the heart forces 

 the blood into them, that the blood 

 goes from the right ventricle 

 through the lungs to the left auricle, 



' All stages of this phase of the argument are 

 not outlined fully. 



