THE DEDUCTIVE METHOD. 



301 



inasmuch m it is possible to study 

 the laws and operations of one human 

 mind apart from other minds much 

 less imperfectly than we can study 

 the laws of one organ or tissue of the 

 human body apart from the other 

 organs or tissues. 



It has been judiciously remarked 

 that pathological facts, or, to speak 

 in comn^on language, diseases in their 

 different forms and degrees, afiford in 

 the case of physiological investigation 

 the most valuable equivalent to ex- 

 perimentation properly so called, in- 

 asmuch as they often exhibit to us a 

 definite disturbance in some one organ 

 or organic function, the remaining 

 organs and functions being, in the 

 first instance at least, imaifected. It 

 is true that from the perpetual actions 

 and reactions which are going on 

 among all parts of the organic econo- 

 my there can be no prolonged dis- 

 turbance in any one function with- 

 out ultimately involving many of the 

 others ; and when once it has done 

 so, the experiment for the most part 

 loses its scientific value. All depends 

 on observing the early stages of the 

 derangement, which, unfortunately, 

 are of necessity the least marked. If, 

 however, the organs and functions 

 not disturbed in the first instance, 

 become affected in a fixed order of 

 succession, some light is thereby 

 thrown upon the action which one 

 organ exercises over another, and we 

 occasionally obtain a series of effects 

 which we can refer with some con- 

 fidence to the original local derange- 

 ment ; but for this it is necessary 

 that we should know that the original 

 derangement was local. If it was 

 what is termed constitutional, that 

 is, if we do not know in what part of 

 the animal economy it took its rise, 

 or the precise nature of the disturb- 

 ance which took place in that part, 

 we are unable to determine which of 

 the various derangements was cause 

 and which effect ; which of them 

 were produced by one another, and 

 which by the direct, though perhaps 

 tardv, action of the original caus^ 



Besides natural pathological facts, 

 we can produce pathological facts 

 artificially ; we can try experiments, 

 even in the popular sense of the term, 

 by subjecting the living being to some 

 external agent, such as the mercury 

 of our former example, or the section 

 of a nerve to ascertain the functions of 

 different parts of the nervous system. 

 As this experimentation is not in- 

 tended to obtain a direct solution of 

 any practical question, but to dis- 

 cover general laws, from which after- 

 wards the conditions of any particular 

 effect may be obtained by deduction, 

 the best cases to select are those of 

 which the circumstances can be best 

 ascertained : and such are generally 

 not those in which there is any prac- 

 tical object in view. The experi- 

 ments are best tried, not in a state of 

 disease, which is essentially a change- 

 able state, but in the condition of 

 health, comparatively a fixed state. 

 In the one, unusual agencies are at 

 work, the results of which we have 

 no means of predicting ; in the other, 

 the course of the accustomed physio- 

 logical phenomena would, it may 

 generally be presumed, remain undis- 

 turbed, were it not for the disturbing 

 cause which we introduce. 



Such, with the occasional aid of the 

 Method of Concomitant Variations, 

 (the latter not less encumbered than 

 the more elementary methods by the 

 peculiar difficulties of the subject,) 

 are our inductive resources for ascer- 

 taining the laws of the causes con- 

 sidered separately, when we have it 

 not in our power to make trial of 

 them in a state of actual separation. 

 The insufficiency of these resources is 

 so glaring, that no one can be sur- 

 prised at the backward state of the 

 science of physiology in which in- 

 deed our knowledge of causes is so 

 imperfect, that we can neither explain, 

 nor could without specific experience 

 have predicted, many of the facts 

 which are certified to us by the most 

 ordinary observation. Fortunately, 

 we are much better informed as to 

 the empirical laws of the phenomena, 



