318 ILLINOIS STATE ACADEMY OF SCIENCE 



instances where one of the twins was a mongol and two 

 where both were mongols. 



The mental affections of twins do not differ in form or 

 in frequency from those of other individuals. A limited 

 number of psychic disturbances have been reported 

 which do not differ from those encountered in children of 

 single birth 



Epilepsy of both children with mental deficiency is 

 reported. A few cases of dementia precox have been re- 

 corded. Hydrocephalus occurred in a pair of twins. One 

 was delivered by craniotomy, the other was born sponta- 

 neously. There was no syphilis or alcoholism in the par- 

 ents. The father was by occupation a painter, but did 

 not suffer from lead poisoning. The second infant died 

 on the twelfth day. 



Soukhanoff made an analysis of thirty-three cases of 

 insanity in twins in 1900. In some there were congenital 

 mental defects, in one dementia precox, in one general 

 paralysis. In most cases the twins were uni-ovular, alike 

 in appearance and mental character, and the form of in- 

 sanity in each pair was the same. 



Infections. According to Orgler's observations, the 

 behavior of twins towards infectious and nutritional dis- 

 turbances was not always the same in both. One twin 

 became ill with bronchitis, Avhile the other developed 

 whooping cough. The first recovered in two weeks, while 

 the latter remained ill for two months. 



They often reacted differently to infectious diseases. 

 One twin died of generalized miliary tuberculosis, while 

 his mate developed tuberculides and a strongly positive 

 Pirquet reaction and the disease ran a more protracted 

 course. In those instances where one twin developed 

 rickets or exudative diathesis, the other had it also, 

 though the intensity of the manifestations was frequent- 

 ly variable, the disease being intense in one child, mild in 

 the other. 



There is also recorded a case of single ovum twins who 

 seemed to be similar physically and mentally, but who 

 showed some difference in their resistance to infection. 

 Whether this difference in resistance is peculiar to one 

 ovum twins cannot be definitely stated. It may be as- 



