i] His Forerunners and Followers. 13 



through the septum is mixed with the air thus drawn in, and 

 by the help of that heat, which is innate in the heart, which 

 was placed there as the source of the heat of the body by God 

 in the beginning of life, and which remains there until death, 

 is imbued with further qualities, is laden with 'vital spirits,' and 

 so fitted for its higher duties. The air thus drawn into the left 

 heart by the pulmonary vein, at the same time tempers the 

 innate heat of the heart and prevents it from becoming ex- 

 cessive. 



Thus from the right side of the heart there is sent to the 

 body generally along the great veins, and to the lungs along 

 the artery-like vein (the pulmonary artery), a flow, followed by 

 an ebb, of crude blood endued with natural spirits only, blood 

 serving the lower stages of nutrition. Blood flows through the 

 artery-like vein (the pulmonary artery) to the lungs for the 

 nourishment of the lungs, just as it flows through the other 

 veins for the nourishment of the rest of the body ; in both 

 cases there is an ebb as well as a flow along the same channel. 

 From the left side, on the other hand, there takes place along 

 the arteries to all parts of the body a flow, followed also by 

 an ebb, of blood endued with vital spirits, and so capable of 

 giving power to the several tissues to exercise their vital 

 functions. As this blood passes from the left heart along the 

 vein-like artery (pulmonary vein) to the lungs it carries with 

 it the various fuliginous vapours which, in the fermenting 

 activity giving rise to the vital spirits, have been extracted 

 from the crude blood, and discharges these vapours into the 

 pulmonary passages. 



Arterial blood, i.e. blood laden with vital spirits, reaching 

 the brain, there generates the animal spirits, which pure and 

 unmixed with blood, existing apart from blood, are carried 

 along the nerves to bring about movements and to carry on 

 the higher functions of the body. 



This Galenic doctrine Vesalius was content to teach. In 

 his great work of 1543 he says, 



" Just as the right ventricle draws blood from the cava so 

 " also the left ventricle draws into itself, each time the heart is 

 " dilated, air from the lungs through the vein-like artery, and 



