^ETIOLOGY. 5 



forming our diagnosis and prognosis, as well as directed in 

 the selection of our prophylactics and special therapeutics. 

 ^Etiology not only tells us of the general causes which induce 

 disturbance, but also of the special causes of special diseases 

 and the modes of their operation. The same causes, we can 

 understand, may produce different diseases; and different 

 causes may develop the same diseases. Still in practice we 

 hnd that the different classes of diseases arise from a limited 

 number of causes. When diseases only arise from certain 

 determinate or specific causes, they are spoken of as specific 

 diseases. 



Various terms have been employed to group or comprehend 

 what are designated as causes of disease ; but for all useful 

 purposes, to regard them as remote and proximate is sufficient. 

 The latter is in reality the condition or conditions of the parts 

 diseased upon which the symptoms depend. The remote are 

 further regarded as ■predisposing and exciting. Predisposing 

 causes are those which confer upon the individual or part a 

 greater susceptibility to be acted upon by the exciting than 

 others differently circumstanced. Exciting causes are such as 

 directly produce the textural changes or disturbances. 

 Neither of these, however, have anything distinctly and un- 

 alterably connected with them which certainly and in all 

 conditions compels them to action in this and no other 

 way. 



Causes are also spoken of as intrinsic or extrinsic, endo- 

 genous or exogenous. The intrinsic or endogenous are all 

 such which in operation owe their existence to inherited or 

 acquired power or potentialities residing in the animal itself. 

 Extrinsic or exogenous include all which act upon the animal 

 from without. 



1. Under intrinsic or endogenous causes of disease may 

 be ranked : 



a. Heredity, such as appear to be capable of propagation 

 from parent to progeny, by which we do not mean that the 

 actual diseased condition is necessarily propagated ; it may be 

 so, but more often it is a tendency or disposition under trifling 

 influences to develop some particular disease or one like it. 



Of some of these conditions w^e are certain ; of others not 

 so. They may be general or systemic diseases, or only local 



