THE CAUSATION OF DISEASE. 6 1 



to contract the disorder. (It is, of course, understood that in all 

 such cases of inherited disease it is a peculiarity of structure 

 which is inherited.) 



I say the peculiarity passes potentially through the opposite sex. 

 This means that the possibility of it exists in this sex, but that 

 it is, in some way or other, kept under and prevented from 

 showing itself. This subject of potentiality is highly interest- 

 ing. Man is a compound of many potentialities, and we can 

 never know what strange property he may show, if only the 

 fitting conditions for its development occur. A large number 

 of such potentialities are inherited from remote ancestors, 

 but this subject will be best considered under the head of 

 reversion. At present we are occupied with sexual heredity, 

 and the tendency of structural potentialities to pass through 

 one particular sex. The special sexual characters of each 

 sex lie dormant in the opposite sex, for if the ovaries or 

 testicles be atrophied, diseased, or removed, the characters 

 of the opposite sex develop. Thus, an old duck has been 

 known to acquire the plumage of the drake ; and " a hen, 

 which had ceased laying .... assumed the plumage, voice, 

 spurs, and warlike disposition of the cock ; when opposed 

 to the enemy she would erect her hackles and show fight. 

 Thus every character, even to the instinct and manner of fight- 

 ing, must have lain dormant in the hen as long as her ovaria 

 continued to act."* Again, the influence of the menopause on 

 woman is very striking : the body is then apt to undergo 

 marked change, and the mental alteration is one affording the 

 psychologist an interesting study. The opposite condition — viz., 

 disease, atrophy, or removal of the testicles — has a like effect, 

 that is to say, the male tends to approach in character to the 

 female. .Now these facts show most strikingly how characters 

 can pass latently through one sex, and manifest themselves in 

 the opposite sex in the offspring — how, for instance, it is 

 possible for a good milking cow to transmit her good qualities 

 through her male offspring to future generations."! But they 

 further explain those cases of non-sexual characters which are 



* "Animals and Plants under Domestication," vol. ii. p. 36. 



\ Ibid., p. 27. Darwin's remarks on this head deserve careful study. 



