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, 



FIG. 15. The stomach of the Darter (Plotus anhinga), 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 



