74 THE CONTROL OF LIFE 



is a-wanting is not in its inheritance, but in its environ- 

 ment. Similarly, stunted growth in infants, or a suc- 

 cession of rickets generation after generation, may imply 

 defective nurture rather than defective inheritance. 



(6) Even when a child is born with symptoms of, 

 or with definite expressions of a disease (a condition 

 to which the term congenital should be applied), it 

 does not follow that the disease was part of the inherit- 

 ance. For there may be microbic infection before 

 birth, e.g., with the animal organism {Treponema palli- 

 dum) that causes syphilis. Similarly, on the other 

 side, there are facts that seem to show that when a 

 mammalian mother has been rendered artificially im- 

 mune to a disease (by the injection of an antitoxin) 

 she may confer this benefit upon her offspring before 

 birth. But this is an early acquirement on the off- 

 spring's part, thanks to its intimate partnership with 

 its mother ; it is not strictly part of the inheritance. 



(c) An attempt must be made to discriminate be- 

 tween the inheritance of a definite disease and the in- 

 heritance of a constitutional proclivity or predisposition 

 towards that disease. Microbic diseases such as tuber- 

 culosis cannot be hereditary, being due to specific infec- 

 tion. Yet they seem to run in famihes. Part of the 

 explanation of this may be the persistence of the same 

 kind of house and habit, and the same abundance of 

 opportunity for infection ; but part of the explanation 

 may also be the actual inheritance of a predisposition, 

 e.g. a ready vulnerabihty of internal surfaces. But 

 the difficulty is to define this predisposition or diathesis, 



