148 THE PHYSIOLOGY OF TWINNING 



comes to bear upon this weakened heart and, if suffi- 

 ciently strong, overwhelms it and brings its rhythm to 

 a standstill. Heart-death ensues as the direct result of 

 its relation with the other twin. This is secondary 

 heart-death. Heart-death from any other cause is 

 primary heart-death and is not a consequence of twin- 

 ning. 



A HEART-DEAD TWIN tCEPT ALIVE BY ITS PARTNER 



While on the one hand a twin may injure its partner 

 by robbing it of its blood supply and suppressing its 

 heart rhythm, a twin which has suffered heart-death on 

 its own account, may, on the other hand, be kept alive 

 by its normal partner. This life-saving act is made 

 possible by means of the third circulation. Were it not 

 for extensive blood transfusion between the normal and 

 the heart-dead twin the latter would die and disintegrate 

 at once. Instead, the heart-dead twin is kept under at 

 least partial circulation so that more or less of the body 

 continues to develop. A completely normal individual 

 cannot, however, be thus reared; for, in the first place, 

 a dead heart cannot revive and therefore atrophies, and, 

 in the second place, the circulation through the placenta 

 from the normal twin is never sufficiently abundant nor 

 energetic to afford nutriment to all parts of the body. 

 Usually those organs situated on the outskirts of the 

 zone of circulation are the first to be deprived of their 

 needed share and are arrested in their development or 

 become secondarily resorbed. For these reasons the 

 prolonging of life in the dependent twin is of no value 

 either to it or to the normal twin. In fact the vicarious 

 heart labor consequent upon the maintenance of an 



