1 82 THE CAUSATION OF DISEASE. 



and stable nervous system, the two may be regarded as a cross 

 in respect of the nervous system, and we should expect the 

 offspring to show a strong tendency to revert to the status quo 

 ante the acquisition of the neurotic state — i.e., to a normal 

 condition of nervous system. 



The Fixity of Structural Characters depends, in large mea- 

 sure, upon their age, ancestral or individual. The ancestral 

 age of serious pathological characters is never great — that is to 

 say, the number of successive generations of the same family 

 afflicted, actually or potentially, with the same serious disease 

 is never great. And such being the case, it follows that there 

 is a strong tendency for the offspring of parents afflicted with 

 serious disease to revert to the normal. In like manner, in 

 regard to characters acquired by the individual himself, the 

 more recent the acquisition the greater is the facility with 

 which it is cast off. 



This principle of " Structural Fixity," taken in conjunction 

 with what we know of the effects of crossing, explains, in large 

 measure, the vis medicatrix natural. 



That the fixity of a structural character largely depends 

 upon its age, ancestral or individual, is well shown under the 

 disturbing influence of disease, in which structural characters 

 tend to disappear in the inverse order of their age ; for almost 

 all disease is a process of dissolution, and, be it noted, so long 

 as the actual process of disease is going on, the dissolution 

 is partial, for, if it be complete, there is death of the part 

 affected, and this is not disease. Since, then, disease is 

 a process of partial dissolution — i.e., an incomplete undoing 

 of evolution — it follows that a number of ancestral characters 

 will tend to display themselves during disease, which must, 

 therefore, be largely tinged with an element of reversion. The 

 reversions, however, which take place during actual disease 

 are very rarely exact reproductions of ancestral states, because 

 the E causing the dissolution is probably always unlike that 

 which was normal to the evolutionary epoch to which the 

 reversion belongs ; and, inasmuch as E is capable of modifying 

 S, the reversion cannot be true : it will be, so to speak, a 

 natural variation of the true reversion. We may, therefore, 

 speak of a disease which is accompanied by distinct dissolution 



