212 Heredity. 



quickness of mind, inconstancy in desires, sudden and variable will. 

 Just as real insanity, says Moreau of Tours, may be hereditarily 

 reproduced only under the form of eccentricity, may be transmitted 

 from progenitors to descendants only in modified form, and in 

 more or less mitigated character, so a state of simple eccentricity 

 in the parents a state which is no more than a peculiarity or a 

 strangeness of character may in the children be the origin of 

 true insanity. Thus, in these transformations of heredity we some- 

 times have the germ attaining its maximum intensity ; and, again, 

 a maximum of activity may revert to the minimum. 



We cannot say what are the causes of these metamorphoses, 

 by what mysterious transmutation nature thus extracts better from 

 worse and worse from better ; for the question is beyond the 

 present range of science. We cannot tell why a given mode of 

 psychic activity is transformed in process of transmission, nor why 

 it assumes one form rather than another. Were the solution of 

 the problem attainable, it would doubtless reveal some singular 

 mysteries. Thus many physiologists have thought that when both 

 parents present the same characteristics, heredity may acquire such 

 power as to destroy itself. Sedgwick thinks that in this way the 

 fact may be explained that two deaf-mute parents oftentimes give 

 birth to children that can hear. In truth, we can only ascer- 

 tain the facts : but this is quite enough, since the facts show by 

 what concurrence of fortuitous circumstances and accidental causes 

 nature produces diversity. 



But these metamorphoses, occurring between generation and 

 generation, will cause us less surprise if we bear in mind that they 

 are also frequent in the same individual. There is no doubt as 

 to this point ; pathology supplies countless instances of it. To 

 restrict ourselves to mental diseases : * Madness,' says Esquirol, 

 ' may affect all forms, either successively or alternatively. Mono- 

 mania, mania, and dementia, alternately replace one another in 

 the same individual.' Thus a lunatic will pass three months in 

 lypemania, the following three months in mania, four months in 

 dementia, and so on in succession, now in regular order, anon 

 with great variations. A lady, fifty-four years old, is one year lype- 

 maniac, and the next year maniacal and hysterical. Often, in the 

 same subject convulsions are seen to pass into epilepsy, epilepsy 



