PRINCIPLES OF PHYSIOLOGY. 



PREFACE. 



We observe, that in a corpse, purely physical and mechanical 

 forces imitate the processes of our bodies, and can originate 

 that motion in its machines, of which in virtue of their structure 

 and composition they are capable. The fluid portions are com- 

 bined and separated according to the laws of gravity, of the 

 power of attraction and repulsion, and remain in equilibrium 

 according to the laws of hydrostatics. When an anatomist 

 injects the vascular system, it is made, by merely mechanical 

 forces, to repeat in some degree its former natural function, 

 according to the laws of hydraulics. The muscle, the fibres 

 which are contracted by cold, keeps the limb in the same posi- 

 tion in which it had placed it, and, by a mere mechanical action, 

 the arteries of a corpse contract and compress the finger when 

 pushed into them, &c. 



These purely physical and mechanical forces are not the pecu- 

 liar forces which usually move the living animal organism in its 

 natural condition, but there are other forces operating in it, ac- 

 cording to a fixed arrangement, and according to laws altogether 

 different from the physical and mechanical laws already known; 

 and it is through these, that the organism performs those 

 natural processes which its structure renders it capable of. 

 That stimulus, which excites no movement in the lifeless heart, 

 or in the perfectly dead muscle, or in the arteries of a corpse, 

 in the natural or living condition keeps up the circulation, 

 changes the pulse in the arteries, and moves the muscles and 

 limbs. Those peculiar motive powers, which give the living 

 organism the advantage over the corpse, although they may 

 co-operate with the purely physical and mechanical forces com- 

 mon to both, T term the proper animal forces, and they 

 communicate to the living animal that nature which I call the 



PROPER ANIMAL NATURE OF ANIMAL ORGANISMS. 



