12 STUDIES IN ADVANCED PHYSIOLOGY. 



through the ventricle of the heart to the lungs (our pulmo- 

 nary artery) . This system he called the venous system and 

 the blood venous blood. This venous blood was dark, being 

 rich in nutritive matter and intended to give to all the 

 organs to which it was distributed the proper substantial 

 nourishing matters. On the left side of the heart and in 

 the arteries there was an entirely different kind of blood, 

 and having no connection in any way w r ith the other or 

 venous blood. This blood he termed the arterial blood. 

 It was lighter in color and weight and carried the vitalizing 

 pneuma dissolved in it which it received in the lungs. It 

 also carried warmth to all parts of the body, which warmth 

 was produced in the left side of the heart. Both kinds of 

 blood ran to all organs, so that each organ could choose 

 whether it wanted the nutritive, rich, thick, venous blood, 

 or the quick, pulsating, active pneuma~conta.inmg arterial 

 blood. It was still believed that the vitalizing influence now 

 dissolved in the liquid blood, the pneuma, caused the prop- 

 erties of sensation and motion. 



Galen, however, adds a new idea to explain the source 

 of the arterial blood. The venous blood is elaborated from 

 the food carried to the liver by the portal vein, but there 

 seemed at first sight no way to account for the production of 

 the lighter arterial blood. The vital spirits were extracted 

 from the air and added to it in the lungs, from which place 

 the blood carried the vital spirits to the left side of the heart, 

 where the finishing touches were given to it, and from which 

 it was sent out over the body. Galen solves this point by 

 admitting that there are pores, very tiny ones though, 

 through the thick ventricular septum, so that the finer parts 

 of the blood from the right side could soak through these 

 invisible openings to the left side. Further he contended, 

 and this seems remarkable now, that the arteries and veins 

 anastomose with each other at their outer ends by means of 

 excessively fine sieve-like canals and pores, so that again 

 some of the lighter parts of the venous blood could gradually 

 soak into the arterial svstem, and so replenish the arterial 



