4 PRINCIPLES OF PHYSIOLOGY. 



The ordinary science of physiology considers the forces of 

 animal organisms in their natural condition, and as they act 

 together in connection with each other, but without distin- 

 guishing the simply physical and mechanical from the proper 

 animal forces. This presupposes that we know the laws accord- 

 ing to which each of these peculiar forces acts separately ; and, 

 indeed, as to the physical and mechanical, whose laws are known, 

 there is in general no difficulty. The physiological w^orks of 

 Haller teach us, in a manner almost impossible to be surpassed, 

 the mechanism of all parts of the animal body, of which the 

 structure developes the functions according to the laws of me- 

 chanics, hydrostatics, hydraulics, optics, acoustics, &c. But do 

 we know those laws by which the proper animal forces govern 

 the body when acting separately from the physical and me- 

 chanical, and independently of them ? Truly, no ! or at least 

 very imperfectly. The thoughts and desires are animal moving 

 forces of the animal organism. But do we at this moment 

 know anything of the laws by which these forces regulate their 

 appropriate organs? or have we hitherto troubled ourselves to 

 observe the operation of these laws in each particular class of 

 ideas and desires ? We have disputed stoutly enough, whether 

 the soul be matter or brain; whether thought be an electric fire 

 or a movement of the vital spirits ; whether souls and bodies 

 exercise a real or an ideal influence on each other ; whether souls 

 form their bodies, or whether they are diffused through them, 

 or dwell only in the head ; whether an instinctive impulse or 

 a passion belongs to the body or the soul ; or whether the vital 

 spirits be elastic or inflexible, electrical or ethereal, &c. All these 

 inquiries will remain for ever inscrutable mysteries, and do not 

 belong to our subject; they can remain altogether uninvestigated 

 without any disadvantage to the real usefulness of theoretical 

 medicine, but we have pursued them with profitless diligence, 

 and have done our best to confuse them more and more. How 

 much have we effected in resolving questions useful to our art, 

 as, for example, in determining by what laws the mind moves the 

 machinery of the animal organism? Under what circumstances 

 the nerves excite sensation ? Under what the sensation becomes 

 an animal moving force, so as to move this or that limb, in such 

 a manner and not otherwise? After what laws the imaginations, 

 the conceptions of the understanding, pleasure, pain, the in- 



