THE CAUSATION OF DISEASE. I 59 



later chapter we shall discuss the question whether structural 

 alteration is a necessary concomitant of disease. The above 

 observations prepare us for the conclusion that some structural 

 change is a constant accompaniment of morbid processes. It 

 is quite obvious that a very large number of disorders are 

 attended by distinct structural changes — e.g., pneumonia, and 

 cirrhosis of the liver. All such diseases constitute distinct 

 natural variations. But even when the E causing the disease 

 produces what seems to be only functional change, there must, 

 according to the arguments just used when speaking of phy- 

 siological functions, be some structural alteration. 



All natural variations, whether physiological or pathological, 

 are, therefore, in the last resort, the same — viz., alterations 

 in structure, wrought by the peculiar action of E. If the 

 action of the E does not tend to break the harmony between 

 the S and the external-E, the variation may be spoken of 

 as physiological ; if, however, it tends to upset, in a very 

 marked degree, what Spencer would term " the equilibrium 

 between the inner and outer forces," it may be spoken of as 

 pathological. The two classes, in fact, pathological and physio- 

 logical, run into one another, and it is by no means an easy 

 matter — as we shall see in another place — to define an ideally 

 normal S. 



Some, however, will be inclined to say that the distinc- 

 tion between pathological and physiological variations is very 

 great, their criterion being this : that all pathological varia- 

 tions are dissolutionary.* There are objections to this view ; 

 but even supposing that physiological and pathological varia- 

 tions are thus sharply separated from one another, the two 

 none the less fall under the great class of natural variations. 

 And my object in the foregoing remarks has been to empha- 

 size this fact — namely, that pathology, being a branch of 

 biology, has to be studied on the same general lines. It is, 

 at all events, convenient to regard all morbid processes as 

 natural variations (temporary or permanent) ; but if some 

 contend that diseased processes need not be accompanied by 



* I am here speaking of actual pathological variations — i.e., of actual dis- 

 ease. For the distinction between actual and sub-pathological variations, 

 vide p. 38. 



