THE LA WS OF HEREDITY. 79 



inclusion under a separate head, may with advantage 

 be here briefly considered. This is what has been 

 called 



HEREDITY AT CORRESPONDING AGES. Here the pecu- 

 liar character may have been transmitted directly from 

 the parents, or it may have been the outcome of 

 reversion in fact, it matters not how it has been 

 acquired, the sole peculiarity to be noticed being the 

 fact that the character makes its appearance at a 

 certain age, and that age is, in the child, the same 

 age as that at which the character had previously 

 appeared in the parent or other ancestor. This 

 peculiarity is most frequently noticed in phthisical 

 families, but it often occurs in cancer, insanity, and 

 other transmitted degenerate conditions. It is a matter 

 of common observation that in some phthisical families 

 the children grow up strong and apparently healthy, 

 but on attaining a certain age the inherited disease, 

 or perhaps I should say the disease, a predisposition 

 to which has been inherited, lights up, and- one after 

 another they die off. Austin Flint, in his excellent 

 " Practice of Medicine," when speaking on this point, 

 says : " This congenital predisposition may remain 

 completely latent until the period of life in which 

 the disease is most apt to be developed; and we 

 sometimes see a whole family of children, one after 

 the other, fall victims to this disease [phthisis], when 

 they severally reach a certain age." Of course our 

 recently acquired knowledge of the character of this 

 disease will modify largely the views once held as to 



