PAPERS ON MEDICINE AND PUBLIC HEALTH 313 



The period of uterine gestation is at best a hazardous 

 one. In addition to those hazards that are met by single 

 embryos and by two egg twins, there are certain very 

 serious special dangers that fall upon one egg twins by 

 reason of their close genetic relationship. One egg twins 

 vary according to the period when the placenta is de- 

 veloped, and consequently one may receive more nutri- 

 ment than the other. Moreover, on account of the differ- 

 ence in the blood supply to the two fetuses, one is more 

 favored than the other, a condition which may even lead 

 to the death of the less favored. Because of these varia- 

 tions in food supply and as a result of one fetus crowd- 

 ing upon the other, there is not only a disproportion in 

 size and weight of the two infants, but malformation and 

 conditions of arrested development may be noted in the 

 weaker twin. Thus, one of the pair may be strong and 

 healthy at birth, the other weak and delicate physically 

 and defective mentally. 



In my practice I have such an instance. The weaker 

 one was extremely difficult to nourish, was very much re- 

 tarded physically, and has remained defective mentally, 

 while the other child developed rapidly and normally. 

 The twins are now fifteen years old, the one a tall, bright, 

 well-developed girl, while her sister is infantile in size 

 and has attained no mental development. I recently saw 

 a pair of male twins, three years old. One was bright, 

 well grown, and his development was perfectly normal. 

 The other weighed only twenty pounds at three years, 

 teeth developed late, and his static development was 

 markedly delayed. He was mentally much retarded and 

 unable to talk. The normal twin's birth weight was six 

 pounds, the other's three pounds. Instances of this kind 

 must be very frequent. 



Dentition may occur at different periods in the two 

 infants, and this does not always depend on the severity 

 of the rickets. In one pair that seemed free from rick- 

 the first dentition" occurred at the seventh month, 

 while the other infant developed his first teeth two 

 months later. At ten months the first infant had eight 

 teeth, while the other had only two. The difference be- 



