Nettling Insects 
49 
itching. It was soon found that this dermatitis was caused by certain 
short, barbed hairs of the brown-tail caterpillars and that not only the 
caterpillars but their cocoons and even the adult female moths might 
harbor these nettling hairs and thus give rise to the irritation. In 
many cases the hairs were wafted to clothing on the line and when this 
was worn it might cause the same trouble. Still worse, it was found 
that very serious internal injury was often caused by breathing or 
swallowing the poisonous hairs. 
The earlier studies seemed to indicate that the irritation was 
purely mechanical in origin, the result of the minute barbed hairs 
36. Browntail moths. One male and two females. Photograph by 
M.V. S. 
working into the skin in large numbers. Subsequently, however, 
Dr. Tyzzer (1907) demonstrated beyond question that the trouble 
was due to a poison contained in the hairs. In the first place, it is 
only the peculiar short barbed hairs which will produce the dermatitis 
when rubbed on the skin, although most of the other hairs are sharply 
barbed. Moreover, it was found that in various ways the nettling 
properties could be destroyed without modifying the structure of the 
hairs. This was accomplished by baking for one hour at no° C, by 
warming to 6o° C in distilled water, or by soaking in one per cent, or in 
one-tenth per cent, of potassium hydrate or sodium hydrate. The 
most significant part of his work was the demonstration of the fact 
