1 84 THE CAUSATION OF DISEASE. 



The tendency which a particular S has to respond abnormally 

 to a particular E may be spoken of as "a specific structural 

 deficiency." The less this structural deficiency, the greater is 

 the quantity of specific mal-E requisite to call forth the dis- 

 order. In other words, the quantity of mal-E requisite to call 

 forth a particular disorder is in inverse proportion to the 

 degree of structural deficiency. Suppose a disease, such as 

 insanity, be represented by eleven units, then the formula 

 S x + E ]0 indicates that the structural deficiency as regards 

 insanity-producing causes — i.e., the tendency of the mind- 

 centres to take on pathological action in response to specific 

 insanity-producing causes — is very slight ; while S 10 + E x 

 indicates a very intense structural deficiency — one, in fact, 

 which will spontaneously blossom into the full disease. 



All of us, even the most typically healthy, respond patho- 

 logically to some forms of E, and it may therefore be thought 

 that the term structural deficiency is inaccurate. The objec- 

 tion would have force, if there were one unchangeable standard 

 or normal S, but such is not the case. If an individual, who 

 would otherwise be accounted healthy, falls a very ready 

 victim to a certain skin parasite, he may be said to have a 

 structural deficiency as regards that parasite, just as an indivi- 

 dual who is incapable of resisting the attack of the tubercular 

 bacillus, or ague poison, may be said to be structurally defi- 

 cient in respect to these agents ; and it by no means follows 

 that the proclivity to disease depends on a weakened and 

 unhealthy bodily state. An individual having a structural 

 deficiency as regards a particular E is, in fact, one who is very 

 ill-adapted to that U, or who, as Spencer might say, is altogether 

 out of equilibrium with it. 



It does not, of course, follow that, because an organism is 

 ill-adapted to its E, disease must ensue. All the weeding-out 

 effected by natural selection is due to ill-adaptation ; but this 

 weeding-out is, except in the case of civilized man, in only a 

 small degree due to disease, which is the result of very signal 

 mal-adaptation of S to E. 



