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 4 
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 i 
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. 
This isolation of villages helps to explain the endemic 
cretinism of Alpine countries. It has been shown, on — 
reliable authority, that cretins are most abundant 
in villages where intercommunication with towns or 
neighbouring villages is difficult, so that the inhabitants 
intermarry freely ; since the introduction of railways 
freer communications have been opened up, and new 
blood introduced in the affected districts ; this has had 
the 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 
