106 HEREDITARY CHARACTERS 



Now it is quite evident that we, as a race, have not 

 acquired immunity to measles. What we have acquired 

 is a high-resisting power to the disease, and the capacity 

 of acquiring immunity individually very readily. With 

 us measles is as a rule a very trivial matter, only the few 

 individuals who have varied away from this inborn capacity 

 succumbing to it. We see that to a race that has not been 

 subjected to any selection with regard to measles, it is very 

 fatal, and has helped in some cases seriously to diminish 

 or even exterminate the native population. It must be 

 borne in mind, that we cannot regard these cases of im- 

 ported disease in quite the same light as the malaria among 

 the West African negroes or measles among the European 

 races. In the case of the imported disease, a race ready 

 to supplant the existing population is necessarily present, 

 and so, before the original race has time to acquire immunity 

 or resistance, the race which has imported the disease takes 

 its place. These are two cases amongst many where races 

 have partially acquired a new character. Whether, if 

 selection went on long enough, complete immunity to such 

 diseases might be obtained, is doubtful. In both these 

 cases, however, the immunity seems to have reached a con- 

 dition where the disease is no longer a danger to the race. 



A comparison between the immunity to tuberculosis in 

 Northern European races, and in races where the disease 

 has only recently been introduced, is also highly instructive. 

 The Northern European races still suffer considerably from 

 the ravages of the tubercle bacillus, but have acquired a 

 considerable degree of resisting power. In towns, almost 

 every one must be infected at some time or other, and 

 very frequently the bacilli live and multiply for some time 

 in the body, being eventually eliminated. Post-mortem 

 examination reveals the presence of tubercular infection in 

 a great proportion of the cases where its traces are sought. 

 " The statement is made by Bouchard that of the post- 

 mortems at the Paris Morgue generally upon persons dying 

 suddenly the percentage found with some evidence of 



