300 THE CAUSATION OF DISEASE. 



mality of S is the capacity of the S for living with a fair 

 measure of health in an average E. It is, as a matter of fact, 

 impossible to pass through life without being exposed over and 

 over again to an E which is abnormal to the vast bulk of the 

 community; every individual must be exposed to a certain 

 quantity of "necessary mal-E," and in our conception of 

 normality we must take into consideration the power of suc- 

 cessfully battling against this — the quality (if I may so put 

 it) , of being affected in a small degree by it, or of readily 

 recovering from the diseases which it causes. And here the 

 element of constitutional vigour comes into consideration. If 

 a weakly individual could live under a carefully regulated E 

 to extreme old age, he would not, in the ordinary sense of 

 the word, though yet he would in one sense, be regarded as a 

 normal man, for he would be incapable of successfully battling 

 against the " necessary mal-E " — against, namely, the average 

 quantity of mal-E. 



This leads us to consider an expression which is often used 

 — "resistance to disease." During life the body possesses a 

 power of resistance, " so that exposure to noxious agents of 

 various kinds does not always, or usually, result in the mani- 

 festations of disease. In this way must be explained the 

 escape of many from what must be regarded as very serious 

 risks." In a limited sense, we are justified in speaking of 

 " resistance " to disease ; but if an individual continually escape 

 unhurt by a so-called noxious agent, it is, perhaps, more 

 correct to say that such an E is not abnormal to that indi- 

 vidual. We should be no more justified in speaking of 

 " resistance " in such a case than of endowing an ordinary 

 individual with a resisting power to the asthma-exciting influ- 

 ence of ipecacuanha. When, however, a person in full bodily 

 vigour is proof against the evil influence of a particular germ, 

 but falls a ready prey thereto when exhausted from any cause, 

 then we may conveniently speak of the natural vigour of the 

 body affording resistance to the evil effects of the specific 

 poison. Unless we are careful, however, this word "resist- 

 ance " may lead us into error. Let us, for instance, consider 

 the following remarks : — 



" We are all of us habitually doing many things, living under 



