THE CAUSATION OF DISEASE. 29 1 



other hand, if there is any peculiarity of the one or of the other 

 which shall lead to pain, or shall cut short by a fraction of 

 time the full term of life, the inter-action is morbid, and S 

 and E are abnormal. 



But another question arises — Can we always be certain that 

 the inter-action is healthful ? Can we always assert con- 

 fidently that a particular E is not working an injurious influ- 

 ence upon the body ? I think not, for a long time may be 

 required to render the evil obvious. An individual, for instance, 

 indulges for many years in alcohol, not, apparently, to an 

 injurious extent, for he seems to enjoy good health. Suppose, 

 however, that, as a result of such indulgence, his life is 

 shortened by never so short a time, it is obvious that, though 

 no evil effect has manifested itself concomitantly with the 

 indulgence, the alcohol has nevertheless all along been operat- 

 ing injuriously. Perhaps in such a case we should be able, 

 on close scrutiny, to detect distinct evil results, such as 

 morning headache, occasional indigestion, or what not ; but on 

 the whole it is doubtful whether the insidious effects would 

 indicate themselves at all at the time. Few, I think, will deny 

 that an injurious E may work altogether silently and unper- 

 ceived. We may take as another instance the case of a man 

 living in London under the most healthy conditions which he 

 can command, and enjoying in his own belief, and, indeed, to 

 ■all appearances, perfect health ; he dies, let us suppose, from 

 causes more or less natural, at the age of seventy. Now, it 

 may well be that, had this man spent the latter years of his 

 life in the country, he would have lived five years longer than 

 he did in London, in which case there could not have been 

 perfectly healthy inter-action, as we have defined it, in London, 

 in spite of no indication to the contrary. 



But although it may not always be easy to say whether 

 healthy inter-action between S and E is taking place, such 

 inter-action, however imperfect our estimation of it, is the only 

 criterion of normality of S and E. 



It must not, however, be supposed from the above remarks 

 that there is no such thing as an absolute and inevitable 

 abnormality of S and E. The following statement sums up 

 the whole truth respecting normality of S and E. 



