THE INHERITANCE OP FAMILY TRAITS 165 



Those who die of tuberculosis are those whose bodies have 

 not been able successfully to combat the genns — ^their bodies 

 have lost in the battle. Family physicians know cases where 

 under bad conditions, overwork, depression of mind and 

 body their patient will begin to decUne and, then, under 

 more favorable conditions begin to build up again. The bat- 

 tle wages now in favor of the one side, now of the other. 

 The result depends quite as much on internal resistance as 

 virulence of the germ. 



That families vary in their internal resistance is well 

 known. Dr. Coolidge of the Lakeville Sanitarium, Massa- 

 chusetts, tells me that he classifies his patients on the basis 

 of their resistance as measured by their response to good treat- 

 ment in the first few days; and he states that the old New 

 England families now show a relatively high resistance to 

 tuberculosis as compared with recent immigrants. 



The Family Histories that have been placed in my hands 

 show the same thing. Though one in ten die of tuberculosis 

 it was not difficult to pick out ten families in each of which 

 about ten persons had died of whom not one had died of 

 tuberculosis. On the other hand there are families with an 

 incidence of consmnption of 75 or 80 per cent. That this is 

 not merely communication of the disease in the families with 

 high death rate follows, of course, when we grant that practi- 

 cally all grown persons are infected anyTvay. It seems per- 

 fectly plain that death from tuberculosis is the resultant of 

 infection added to natural and acquired non-resistance. It 

 is, then, highly undesirable that two persons with weak re- 

 sistance should marry, lest their children all carry this weak- 

 ness. 



Pneumonia. — Since the germ of pnemnonia is a normal resi- 

 dent of our throats, the disease is not due merely to infection; 

 but to a weakening of a natural or acquired resistance. Our 

 Family Records show again and again the heavy incidence of 



