166 THE GROWTH OF GROUPS 



frequently born to the same parents. " The brothers " 

 are conspicuous in many asylums. In Tanzi's well- 

 known book on mental diseases there is a photograph 

 of three sisters, all victims of the disorder, who are alike 

 even in feature. 



Let us now consider some of the opinions held in 

 regard to the nature of Dementia prcecox. Some writers 

 uphold the atavistic theory and regard persons afflicted 

 with the disorder as reversions. They compare dis- 

 ordered action to " monkey- tricks " and draw special 

 attention to the so-called signs of degeneration, especially 

 to certain characteristics of the ear and hand, which are 

 said to be peculiarly frequent in demented persons. Many 

 of these peculiarities, however, may be seen in persons 

 commonly regarded as normal. The so-called simian 

 hand is said to be common in dementia. This type of 

 hand is described as long and narrow with a thumb less 

 " opposable " than usual. The hands of the many 

 species of apes and monkeys display a great variety of 

 shape, they are not always long and narrow. It is 

 scarcely possible to construct an ideal simian hand from 

 nature, but in some monkeys the plane of the thumb nail 

 is at right angles to the plane of the finger nails when the 

 hand is flat ; that is to say it is more, rather than less, 

 " opposable " than in man. 



The term reversion which contains, so to speak, the 

 essence of the atavistic explanation of dementia, is of 

 course borrowed from biology, it is well therefore to 

 note that this term is no longer in general use among 

 biologists. 



The atavistic theory does not find many supporters. 

 There is one grave objection to it. As Tanzi points out, 



