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be one of disordered association only ; comparison, or association, of 

 what? of ideas; or of that which is not obtained from parents, or 

 possessed by the ovum. It is perfectly clear, that if a man were born 

 of mad parents, and had in ever so strong a degree the hereditary 

 taint, he never could have either of the above forms of insanity, viz. 

 of disordered comparison or disordered association of ideas, if he were 

 so circumstanced from his birth as to be precluded the acquisitions 

 from externals, as, if he were enclosed in a dark room and never 

 permitted to hear an articulate sound. Yet in these forms of 

 insanity the predisposition is hereditary, although the form itself is 

 principally constituted by the acquirements from without, and de- 

 pendent perhaps upon education and a long train of connected 

 causationi In this case, although the acquired properties or ideas 

 have a principal share in immediately constituting the insanity, and 

 in determining the consequent acts of volition, yet we must suppose 

 the predisposition to ideas to have a share, or in fact, if it is a 

 principle of consciousness, to be the basis of their individual 

 existence. Here, then, we may look for the cause, or a cause, of 

 the insanity; and as the insanity cannot arise out of the mere pre- 

 disposition, but is principally dependent upon relations of ideas, so 

 in this, as in the corporeal instances, we perceive the probability 

 that the original and the acquired properties are mixed in the 

 causation of progressive phenomena ; and in this case too, as in the 

 other, we perceive the impossibility of pronouncing, such a share 

 have the original, and such the acquired properties in these occur- 

 rences. We must for the present be content with our alternatives. 



31. From this view it appears that we cannot fix a period to 

 the commencement of the processes which are preparatory to 

 disease; the necessity of a progressive change, leading up to this 

 state of disease, is demonstrable; and, with respect to the causes 

 which constitute the disease, we cannot lay down any general 

 criterion by which to distinguish whether they belonged to the 

 ovum or whether introduced from without. In cases of contagious 

 and infectious disease, &c. we know that a cause is obtained exter- 

 nally; but the share of this cause and that of the original proper- 

 ties, as we may conjecture that they produce effects in conjunction, 

 we cannot even here discriminate. 



32. That state of the properties which is the stage of pro- 

 gressive change, immediately preceding disease, is called predis- 

 position ; any change, the tendency of which is finally to impair 

 functions, &c. may be said to comprise a diseased state. But there 

 is convenience in the distinction between predisposition and disease: 

 according to our notion of the difference between these two, pre- 

 disposition is a change of the state of perfect health which does not 

 produce symptoms: disease is also a change of the state of health, 

 but it is manifested by symptoms : the former change is not related 

 with our faculties of perception, &c.; the latter change is related 

 with our faculties of perception. The most healthy state may be 



