recently as in the time of Albert von Haller (approximately 1760-1780) physicians still continued to believe that it was the function of respiration to cool the blood; and indeed it was scarcely possible before 1800 to offer a more correct physiology of the act of breathing, for it was not until after the lapse of many centuries that the advance in our knowledge of chemistry reached a point at which it became possible to find a satisfactory solution of so complicated a problem.
As to the nature of the blood itself Galen believed, as I have already stated more fully in Part I. ("Ancient Medicine"), that there are two kinds—spirituous blood (or spirit) and venous blood. He gave the name of spirituous blood to that which is found circulating in the arteries, and which is appreciably brighter in color than that which fills the veins. According to Flourens, the distinguished French physiologist of the nineteenth century, Galen was the first among the ancient anatomists to make this distinction of two different kinds of blood. To the spirituous variety Galen ascribed the function of nourishing the more delicately constructed organs like the lungs, while he claimed that the venous blood is suited to nourish only the coarser ones, like the liver, spleen, etc.
In his further development of a physiology of the circulation of the blood Galen, who as a rule expresses his ideas with great clearness, makes statements which I find it extremely difficult to comprehend. I am therefore tempted to assume that the copyists, to whom we are indebted for handing down his actual words from age to age, are the persons upon whom should be cast the blame for the obscurity of which I complain. However this may be, it is an unquestionable fact that the ablest physiologists, were they to be confronted to-day with the duty of solving this problem of the circulation under the conditions of knowledge which existed during the third century of our era, would surely not be able to provide a more correct solution than that which is credited to Galen. The problem was attacked repeatedly by some of the brightest and best-equipped minds of the Renaissance period, but not one of
