CHAPTER XIX. 



The Symbolical Method of Expressing the Kelative Share taken by- 

 Structure and Environment in Causation. 



We shall do well, if we can, to assign to S and E respectively 

 their relative share in the production of any given case of 

 disease — to say what is the extent of the structural deficiency, 

 and what the intensity of the mal-E. 



Since disease depends upon an inter-action of S and E, 

 it is obviously impossible to eliminate E from causation, even 

 though the disease burst out spontaneously under the most 

 favourable E. But if the inherent tendency to disease in any 

 individual be so strong that the disease must needs break out, 

 no matter how favourable the E, we may, for all practical 

 purposes, eliminate the share of E in its causation. In such a 

 case the individual may be said to contain within himself the 

 full potentiality of the disorder. 



In considering the degree of structural deficiency, or pro- 

 clivity to some particular disease, we shall discover two 

 extremes. At one extreme end we have the class of cases 

 whereof mention was just now made — namely, in which the 

 proclivity to a particular disease is so great that it must needs 

 break forth under the most favourable Environment ; and at 

 the other extreme, a condition of S which refuses altogether 

 to be thrown into morbid action under the most intense 

 pathogenic E possible. These remarks do not, of course, 

 apply to all pathogenic E's, for there are many mal-E's which 

 excite disease in all alike — e.g., prussic acid, or the continued 

 breathing of foul air. Be it noted, moreover, that, by struc- 

 tural deficiency, or proclivity to disease, I wish to denote 

 proclivity towards some special disease. While a vast number 

 of specific E's will produce disease in all mankind, each one 

 -does not always produce the same disease. Prussic acid, e.g., 



