ENLARGEMENT OF PARTS FROM USE. 27 
in lambs. In Britain sheep and lambs are often turned 
out to feed on clover grown in fields with the stubble 
from a previous crop of wheat remaining ; the short, 
stiff, hard ends of the straw irritate the mouth and nose 
as well as the tender part of the feet above the coronet, 
oid, 
WIN 
a lif 
I, 
Fic. 15.—The stomach of the Darter (Plotus wnhinga), showing 
the hairy pyloric plug (Mus. Royal College of Surgeons). 
and produce a crop of warts. The relation of such 
irritation to warts is demonstrated by the fact that when 
the lambs are removed from the stubble the warts dis- 
appear. Similar warts grow on the hands of children 
