INTRODUCTION. 475 



cause is scarcely to be distinguished from his definition of dis- 

 ease. 



" It has been common to divide causes into external and tn- 

 ternal) the last comprehending whatever has subsisted for some 

 time before it produced its effects upon the body, the first, 

 whatever is applied from without, and immediately operates its 

 effects. There is often some use in this distinction of causes ; 

 but it is a great mistake to suppose that it implies the same as 

 that between remote and proximate causes ; there may be in- 

 ternal causes which are not proximate, and external causes which 

 may be considered as a part of the proximate. 



" Another distinction with regard to causes, viz. that into the 

 predisposing and exciting causes, deserves attention ; as, when 

 an effect is produced by a particular agent acting upon a par- 

 ticular subject, which agent would not have acted upon every 

 subject. Thus to recur to my former illustration, in order 

 to kindle gun-powder, a spark can be produced only by the 

 collision of two certain bodies, flint and steel. The collision of 

 flint with soft iron will not produce the effect, which will there- 

 fore depend upon a concurrence of causes. Now the human 

 body is at different times in different conditions with regard to 

 its fitness for being acted upon by particular agents ; such a 

 condition is called a Predisposition, and the causes which pro- 

 duce it are termed predisposing causes. All those agents, on 

 the other hand, which produce their effects only under certain 

 conditions, are called occasional or exciting causes." 



IV. The cure of diseases is chiefly, and almost unavoidably, 

 founded in the knowledge of their proximate causes. This re- 

 quires an acquaintance with the Institutions of Medicine ; that 

 is, the knowledge of the structure, action, and functions of the 

 human body ; of the several changes which it may undergo ; 

 and of the several powers by which it can be changed. Our 

 knowledge of these particulars, however, is still incomplete, is 

 in many respects doubtful, and has been often involved in mis- 

 take and error. The doctrine, therefore, of proximate causes 

 founded upon that knowledge, must be frequently precari- 

 ous and uncertain. It is however possible for a judicious 

 physician to avoid what is vulgarly called theory, that is, 

 all reasoning founded upon hypothesis, and thereby many of 



