72 MARRIAGE AND DISEASE. 



insanity, epilepsy, scrofula, and gout, while the latter 

 diagonal is said to be most frequently observed in 

 cases of structural peculiarity. 



II. KEVERSIONAL HEREDITY or ATAVISM. "This is 

 a term used to denote cases in which a child, instead 

 of resembling its immediate parents, resembles one of 

 his grandparents or still remoter ancestor, or even 

 some distant member of a collateral branch of the 

 family " (Lucas). This is a very common form of 

 heredity. To recognise some peculiar character in the 

 grandchild which is absent in the parent, yet strongly 

 marked in the grandparent, may be said to be an 

 almost everyday occurrence. In some diseases 

 pathological variations this mode of transmission is 

 so regularly followed that these diseases have come 

 to be looked upon as only attacking every other gene- 

 ration. Gout thus frequently attacks only alternate 

 generations, and there are several other diseases which 

 at times follow the same rule ; therefore it should be 

 understood that the absence of a " family disease " in 

 one generation is no evidence that the taint has been 

 shaken off and got rid of, and will not appear in the 

 next generation. Sir William Aitken states his opinion 

 that "a family history extending over less than three 

 generations is almost worthless, and may be misleading." 



This reversional form of heredity is to be explained 

 in this way : Where the peculiar character transmitted 

 belongs to what might be called the physiological class, 

 it may be taken that its reappearance in the family is 

 the result of the action of the natural tendency to 



