nERI<]DITY AND DISEASE 107 



(luced within the body of the mother. Profoundly 

 interesting and important all this doubtless is ; and so 

 are a hundred other cases more or less parallel with 

 it, such as the killing of the child by the giving of 

 poison to its mother, or the possible treatment of the 

 suckling child, after birth, by giving castor oil to its 

 mother. But these are not cases of heredity, save in 

 so far as the child's tissues inherit those characters of 

 the maternal tissues which make them respond in cer- 

 tain fashion to the action of the rheumatic toxin, or 

 mercury, or castor-oil. This we now see clearly, but it 

 is well to remember the totally dillerent aspect which 

 the facts necessarily wore when the nature of rheu- 

 matic fever was unknown. Meanwhile there remain 

 not a few^ diseases, such as gout, of which the causation 

 is still unexplained and about the inheritance of which 

 it will be well to preserve some reticence until haply 

 we may " know what we are talking about." 



But before we leave this part of our subject we may 

 note one or two very interesting facts which, as we 

 are now able to recognise, are not facts of heredity, 

 though they may appear to be such at first sight. 

 We have already observed how the passage of poisons 

 from the blood of a mother to the blood of the 

 unborn child may give rise to the appearance of 

 inherited disease. Similarly a child may acquire 

 immunity from various diseases or poisons, but this 

 immunity is acquired — not inherited, or innate, or 

 "natural." For instance, Ehrlich, the greatest living 

 authority on immunity, has shown that the oflspring 

 of mice who had acquired an imnuinity to the action 

 of certain poisons, were themselves immune, if both 

 parents or the mother alone had been immunised ; 



