106 HEREDITY 



heart, especially those of the left side of the heart, 

 which is subjected to greater strain. But these 

 poisons, or toxins (the plural is used not because 

 there is definite evidence that there are more than 

 one, but because we know little of their nature as 

 yet, the diplococcus having only very recently been 

 discovered), are also contained in the blood which 

 the mother sends to the placenta ; and that organ is 

 apparently unable to prevent their passage from the 

 maternal to the foetal circulation. Hence the toxins 

 may attack the heart of the child, especially the 

 valves of the right side, which are subjected to the 

 greater strain in intra-uterine life. The child is thus 

 born with " congenital heart-disease," or, to use the 

 doctor's slang, " a congenital heart." Now, observe the 

 broad results as they would appear, say, thirty years 

 ago, when the bacterial origin of rheumatic fever 

 was not even suspected. The mother has the rheu- 

 matic " diathesis," or "constitution," or "dyscrasia" 

 — the Qfreater the iOTorance the more luxuriant the 

 terminology — which results in heart-disease. The 

 child is born with heart-disease absolutely identical 

 save for a slight difference in its site. Plainly the 

 child has inherited the maternal " diathesis." 



But now we know the actual facts of the case, and 

 we perceive that they really have nothing to do with 

 the problems of heredity proper. The baby's heart- 

 disease is not due to its having inherited the " rheu- 

 matic diathesis " from its mother, but to the circum- 

 stance that during its life within the mother certain 

 poisons circulating in the mother's blood happened 

 to pass into its blood and, as is quite intelligible, 

 caused injuries within its body similar to those pro- 



