Nettling Insects 49 



itching. It was soon fotind 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 cotdd be destroyed without modifying the structure of the 

 hairs. This was accomplished by baking for one hour at iio^ C, by 

 warming to 60° 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 



