G8 ON THE STUDY OF PHYSIOLOGY. 



verbal and metaphysical puzzles, and the misplaced exer- 

 tions of the imagination, will make no impression. 



Now, although certain parts of the animal economy 

 obey the laws of mechanics, and others admit of illustration 

 by the aid of chemistry, and thus far the living processes 

 come within the domain of the physical sciences, the main 

 springs of the animal functions, the original moving forces, 

 cannot be explained on these grounds. The powers of 

 sensation and contraction, and the properties of the capil- 

 lary vessels, belong peculiarly and exclusively to living 

 organic textures : they are eminently vital, and form the 

 distinguishing character of living beings. We learn them by 

 observation, as we learn the properties of dead matter, and 

 we know nothing more than the fact, that certain vital ma- 

 nifestations are connected with certain organic structures *. 



* Since I delivered these Lectures, I have become acquainted with Dr. 

 Brown's Inquiry into the Relation of Cause and Effect, third edition, 8vo. 

 Edinburgh, ISLS ; a most instructive work, calculated to dispel much of 

 the obscurity and confusion, by which both physical and mefapliysical dis- 

 cussions have been perplexed and retarded, and to interest strongly all those 

 who derive pleasure from perspicuous language and close reasoning. As it is 

 extremely important to possess clear notions of causation, of the relations 

 expressed by the words cause, effect, property, quality^ power, 1 subjoin an 

 extract, in which these matters are more satisfactorily explained tlian in any 

 other book I have met with. 



*' It is this mere relation of uniform antecedence, so important and so 

 universally believed, which appears to me to constitute all that can be philo- 

 sophically meant, in the words power or causation, to whatever objects, 

 material or spiritual, the words may be applied. If events had succeeded 

 each other in perfect irregularity, such terms never would have been invented ; 

 but when the successions are believed to be in regular order, the importance 

 of this regularity to all our wishes, and plans, and actions, has of courseled 

 to the employment of terms significant of the most valuable distinctions 

 which we are physically able to make. We give the name of cause to the 

 object which we believe to be the invariable antecedent of a particular 

 change ; we give the name of effect, reciprocally to that invariable conse- 

 quent ; and the relation itself, when considered abstractedly, we denomi- 

 nate power in the object that is the invariable antecedent — susceptibilitif in 

 the object that exhibits, in its change, the invariable consequent. We say 

 of fire, that it has the power of melting metals ; and of metals, that they are 

 susceptible of fusion by fire,— that fire is the cause of the fusion, and the fu- 



