ON THE STUDY OF PHYSIOLOGY. 63 



power in the former organ, the quantity of blood arriving at 

 and departing from it, the elastic and other properties of the 

 vessels, their various capacities, the resistance of the column 

 in the arteries and veins, the density and cohesion of the 

 blood, and many other points : — and to know all these with 

 perfect accuracy. Even if all this were accomplished, the 

 great number of elements entering into such a theory would 

 conduct us to impracticable calculations. It would be the 

 most complex case of a problem, which is extremely difficult 

 of solution in its simple state. The ablest geometricians, 

 sensible of these difficulties, speak of the operations of liv- 

 ing bodies with a modest caution, to which the bold calcu- 

 lations of some physiologists form a striking contrast. They 

 acknowledge that the springs of the animal frame are too 

 numerous, too intricate, and too imperfectly known, to be 

 submitted, with any prospect of advantage, to calculation ; 

 that, in such complicated operations, experience is our only 

 safe guide, and inductions from numerous facts the only 

 sure support of our reasonings. The most just calculations 

 on such subjects can merely appreciate our ignorance ; 

 which may indeed be concealed, but cannot be removed, by 

 the vain parade of a science foreign to medicine. 



If we define chemistry as the science which teaches us the 

 composition of bodies, explaining the laws, according to 

 which their elementary particles act on each other, when 

 brought into contact, the combinations or separations whicli 

 result from their affinities, and the circumstances which 

 promote or obstruct the action of those affinities, we must 

 allow that many of the animal processes exhibit to us che- 

 mical operations. Such are the changes wrought upon the 

 food by the solvent juices of the stomach, and by the admix- 

 ture of bile, pancreatic liquor, and intestinal secretions ; the 

 new combinations, which the elements of the blood enter 

 into in the glands, the membranes, and the skin, and in the 

 texture of the various organs, so as to exhibit to us a new 

 set of products ; the conversion of chyle and lymph into 

 blood ; and the mutual action of this fluid and the atmos- 

 phere in respiration. 



