1:50 HISTORY OF PHYSIOLOGY. 



umpire between Aristotle and Galen ;" or rather, he might have said, 

 to see how, in the promotion of science, sense and reason, observation 

 and invention, have a mutual need of each other. 



We may observe further, that though Harvey's glory, in the case 

 now before us, rested upon his having proved the reality of certain 

 mechanical movements and actions in the blood, this discovery, and all 

 other physiological truths, necessarily involved the assumption of some 

 peculiar agency belonging to living things, different both from mechani- 

 cal agency, and from chemical ; and in short, something vital, and not 

 physical merely. For when it was seen that the pulsation of the heart, 

 its systole and diastole, caused the circulation of the blood, it might 

 still be asked, what force caused this constantly-recurring contraction 

 and expansion. And again, circulation is closely connected with respi- 

 ration ; the blood is, by the circulation, carried to the lungs, and is 

 there, according to the expression of Columbus and Harvey, mixed 

 with air. But by what mechanism does this mixture take place, and 

 what is the real nature of it ? And when succeeding researches had 

 enabled physiologists to give an answer to this question, as far as che- 

 mical relations go, and to say, that the change consists in the abstrac- 

 tion of the carbon from the blood by means of the oxygen of the atmo- 

 sphere; they were still only led to ask further, how this chemical 

 change was effected, and how such. a change of the blood fitted it for 

 its uses. Every function of which we explain the course, the mecha- 

 nism, or the chemistry, is connected with other functions, is subser- 

 vient to them, and they to it ; and all together are parts of the gene- 

 ral vital system of the animal, ministering to its life, but deriving their 

 activity from the life. Life is not a collection of forces, or polarities, 

 or affinities, such as any of the physical or chemical sciences contem- 

 plate ; it has powers of its own, which often supersede those subordi- 

 nate relations ; and in the cases where men have traced such agents in 

 the animal frame, they have always seen, and usually acknowledged, 

 that these agents were ministerial to some higher agency, more diffi- 

 cult to trace than these, but more truly the cause of the phenomena. 



The discovery of the mechanical and chemical conditions of the 

 vital functions, as a step in physiology, may be compared to the dis- 

 covery of the laws of phenomena in the heavens by Kepler and his 

 predecessors, while the discovery of the force by which they were pro- 

 duced was still reserved in mystery for Newton to bring to light. The 

 subordinate relation of the facts, their dependance on space and time, 

 their reduction to order and cycle, had been fully performed ; but the 



