Congenital Cardiac Disease in Identical Twins.

The studv of rare diseases and rare abnormalities is of more valuie in throwing light upon pathological or physiological processes than in furnishing guidance for futuire enc-xunter with the same condition. This principle applies to the study of diseases in the individual, but it applies even more in the case of homogeneous twins, for here the solutions of embryological problems may become apparent, and a means is afforded of investigating the influence of the various factors which control development in childhood. The roles of nurture and nature in directing character formation have thus been investigated by Galton1. The occurrence of acquired disease, both plhxsical and psychical, in homogeneous twins has elucidated the close similarity of intimate structure and defence mechanisms possessed by such twins. In this connection, twins suffering from lienteric diarrhcea have been recorded by Cockayne2, while asthma occurring in both of a pair has been. described bv Trousseau3. Cases of congenital abnormalities occurring doubly in twins have been investigated and recorded by Cockayne2, who found suich abnormalities involving not only gross and intimate struieture but mental and metabolic processes also. The rarity of congenital cardiac abnormalities in twins, and the writer's recent observation of twins suffering fronm patent duetuts arteriosus, have prompted an iinvestigation of car(liae defects occurring in paired offspring, and specially a consi(leration of the clinical manifestations of patent ductuis arteriosus in infants. This paper therefore deals first wN-ith congenital ca.rdiac disease in homogeneouis twins, an account being given of cases recently observed, and secondly with the synmptomis of patent ductus arteriosus. In the latter part other examples of this defect occurring solitarily in single children have been collected for their clinical valuie, and the syndrome has been described.