24 THE CAUSATION OF DISEASE. 



alteration of the external-body-E. A decayed tooth may 

 cause neuralgia or dyspepsia, and thus, in an indirect way, 

 bring about a universal modification of cell-E.* 



Diseases, then, may be roughly classified into the general 

 and the local, but it is difficult to draw the dividing line sharply 

 between them, few diseases being local in the strict sense of 

 the word. We meet, in fact, with every possible grade 

 between a strictly local and a thoroughly general disease. 

 Scarlatina is a typical general disease : in it rapid and pro- 

 found changes are wrought throughout the body. Organic 

 heart disease might be accounted local, at all events in its 

 early stages, although it eventually becomes general, and, 

 indeed, the most strictly general diseases usually begin locally 

 — that is, in one particular tissue. Some few, however, have 

 a more general origin, such as the specific fevers, for although 

 the poison is commonly introduced through one particular 

 tissue, it is rapidly disseminated throughout the body. Scurvy, 

 too, cannot be said to originate in any particular tissue : it is 

 really due to a universal mal-E, some essential element in the 

 blood being absent. f 



Disease, it has just been said, usually begins locally. When 

 this is the case it is of the first importance to specify, if we 

 can, the tissue first affected, and the nature of the E acting 

 upon it.J 



* Supposing a condition such as atheroma or fatty tumour to be strictly 

 local, and supposing, moreover, that it cause no trouble or inconvenience what- 

 ever to the individual, the question arises : are we justified in regarding it as 

 disease ? I have no hesitation in saying that we are not justified in regarding 

 it as actual disease. If it contain within it the germ of some future mischief : 

 if a fatty tumour be destined one day to press upon some nerve and cause 

 pain, or if an atheromatous patch be but the germ of a future aneurism, then 

 we have in these two diseases examples of potential but not actual diseases. 

 We have no more right to speak of them as actual diseases than we have to 

 assert that an individual is afflicted, in the embryo, with all those diseases 

 which he is destined to suffer. The mere possession of obvious structural 

 abnormality does net, in my mind, constitute actual disease. 



f. The use of the term " blood disease " in medical literature is very mis- 

 leading, for, owing to the mutual dependence of tissue upon tissue, there are 

 few, if any, general diseases in which the blood is not sooner or later involved. 



X In order to complete our knowledge of causation, it would be further 

 necessary to discover the part played by structural weakness of the affected 

 tissue. If we can assign to E and S respectively their proper share in causation 



