THE CAUSATION OF DISEASE. 305 



we often discover in the cadaver marked structural abnormality, 

 to say nothing of minor structural abnormalities, such as small 

 atheromatous patches, which may give no evidence of their 

 existence during life by altered function. I shall presently 

 discuss the question whether we are justified in regarding all 

 such minor structural changes as distinct abnormalities. 



Having, then, in the above tests, a means whereby an ap- 

 proximate criterion of abnormality may be obtained, let us now 

 inquire how far structural abnormality occurs during actual 

 disease. 



It has been over and over again remarked that disease may 

 result from abnormality of S, abnormality of E, or abnormality 

 of both. Given any of these, an abnormal inter-action must 

 ensue. When the E alone is abnormal, we theoretically 

 assume the S to be normal — that is, normal when the abnormal 

 E first acts upon it ; the propositions take no account of the 

 condition of the S during the abnormal inter-action — whether 

 or not, namely, it retains its normal structure. 



In respect of this question, we may divide diseases into two 

 classes : — 



1. Diseases accompanied by obvious structural abnormality 

 of tissue, as determined by macro- or microscopic exami- 

 nation. 



2. Diseases in which there is no discoverable abnormality 

 of tissue. 



This latter class falls into two subdivisions : — 



a. Diseases in which the S acted upon is normal at the time 



the nocuous E acts upon it, as may happen, for instance, 

 in poisoning by opium and in indigestion from a gross 

 error in diet. The E in such cases is for the most 

 part a necessarily mal-E — that is, one which would 

 produce an injurious effect upon all. (I say, for the 

 most part, because individuals differ in their response 

 to poisons and indigestible articles of food.) 



b. Diseases in which the S is abnormal at the time the 



nocuous E acts upon it, as epilepsy, insanity. In these 

 cases the E calling out the disease need not be a 

 necessarily mal-E. 



