162 THE CAUSATION OF DISEASE. 



apartment where a European, recently landed, is exposed to the 

 attacks of pulex penetrans."* There is no occasion to pursue 

 this subject further, for it is known to all that certain indi- 

 viduals refuse to respond morbidly to E's which are capable of 

 setting up distinct morbid action in others. 



But among such as do respond there is vast difference in 

 respect of the readiness of response to any particular pathogenic 

 E. This " readiness of response " signifies the inherent tendency 

 to particular diseases, and may be spoken of as structural 

 deficiency. Many persons would quarrel with this term, since of 

 two individuals, one of whom, we will suppose, is proof against 

 the attack of the common flea, while the other is exceedingly 

 liable to be bitten by it, they would be unwilling to attribute to 

 the latter a structural deficiency, although, no doubt, they would 

 allow the term in the case of an individual who responded 

 readily to a gouty or tubercular E ; but we shall see, in another 

 place, that normality and abnormality of structure are relative 

 terms, and can only be considered in relation to E. If S-f E 

 be such that healthful inter-action results, then both may be 

 regarded as normal, but if S+this same E = disease, then S is 

 abnormal in regard to that E, and, therefore, the term structural 

 deficiency, used in this relative sense, is justifiable. 



We may have any degree of structural deficiency, or ten- 

 dency to particular disease. In the case of such diseases as gout, 

 tubercle, or cancer, we may, perhaps, speak of this deficiency 

 as an actual " disease taint" but in many cases of structural 

 deficiency there is obviously no condition of tissue meriting 

 this designation, as when an individual is structurally deficient 

 as regards certain skin parasites. In thus speaking of the 

 intensity of disease proclivity, I wish to denote the quantity 

 of pathogenic E necessary to call forth the actual disease — 

 the less the structural deficiency, the larger the quantity of 

 pathogenesis needful to call forth the actual disease, and vice 

 versa. Wherefore we arrive at this principle : the c^iiantity of 

 mal-E needful to call forth disease is in inverse ratio to the 

 structural deficiency. 



* Quoted by Darwin, " Variation under Domestication," vol. ii. p. 265. 



