^V 194 EVOLUTION AND DISEASE. 



if not impracticable. The inhabitants, thus cut off from 

 the outside world, intermarried very freely. At the end 

 of the last century sexdigitism, both of the hands and 

 feet, suddenly appeared, and in thirty-five or forty years 

 almost the entire population was thus affected. When, 

 in 1829 and 1836, says M. Potton, I observed this 

 strange phenomenon it was present in some subjects 

 only in a very rudimentary manner ; amongst many it 

 was only a large tubercle containing a hard osseous body, 

 and fixed to the side of the thumb, a more or less well- 

 formed nail terminating it. At this time the influence 

 of crossing, due to the opening-up of communications, 

 was making itself felt. In 1847 I had occasion to see 

 a foreman, originally from this locality, who married and 

 settled in Lyons. He was affected with the malforma- 

 tion, but was the father of four normal children. At the 

 time of writing, he goes on to say, the anomaly has 

 almost completely disappeared from the district. 

 r This isolation of villages helps to explain the endemic 

 retinism of Alpine countries. It has been shown, on 

 eliable authority, that cretins are most abundant 

 i villages where intercommunication with towns or 

 eighbouring villages is difficult, so that the inhabitants 

 ntermarry freely ; since the introduction of railways 

 reer communications have been opened up, and new 

 lood introduced in the affected districts ; this has had 

 tie effect of diminishing the number of cretins. 



This condition of things is illustrated by the following 

 example : There is preserved in the museum of the 

 Royal College of Surgeons a fish with a large tumour 

 growing from its side. It was suggested that the pond 



