TIIK BROWN-TAIL Morn. 143 
of cases of this poisoning; I should s;iy nearly a hundred 
cases in all came under my observation. The irritation 
seemed to remain and was much worse than that caused by 
poison oak or poison ivy, and was not so easily gotten rid 
of. I treated most cases with some cooling application. 
Some cases were decidedly obstinate, but no case was seri- 
ous enough to menace the life of the patient." 
Nettling may be produced, as we have learned from ex- 
perience, by the younger stages, even those in the webs, 
where they are freely handled by one with a tender skin. 
No inconvenience would occur to anyone, however, from 
handling the unopened webs, and rarely will the young 
caterpillars be annoying. 
The cause of the nettling has been recently investigated 
by E. E. Tyzzer, A. M., M. D., Assistant in Pathology, Har- 
vard University, and Director of Research, Caroline Brewer 
Croft Cancer Commission, who has reported on the "Path- 
ology of the Brown-fail Moth Dermatitis." His conclu- 
sions are as follows :* 
'The most important facts thus far ascertained con- 
cerning the brown-tail moth dermatitis may be summarized 
as follows : 
The lesions are produced by the penetration into the epidermis of pecu- 
liarly modified microscopic hairs, the nettling- hairs, which are sharply 
pointed and barbed for their entire length. The other hairs of both the 
caterpillar and moth do not produce any dermatitis. 
These nettling hairs develop on the caterpillar, but are also found, as the 
result of direct transference, on the cocoons, moths, egg masses and in the 
winter webs, and are blown about in the air. They develop on the subdorsal 
tubercles of the fifth and sixth segments of the young caterpillars, but are 
much more numerous as the caterpillars attain' their growth, being then 
found on the subdorsal and the lateral tubercles from the fifth to twelfth seg- 
ments inclusive. The caterpillars are then very poisonous. 
The nettling hairs, which from their shape are perfectly adapted for pene- 
tration, possess in addition an irritating substance which" is, undoubtedly, an 
important factor in the production of the dermatitis. 
This substance may be destroyed by heating the nettling hairs at 115 C. 
either in a fluid or with dry heat, or it may be extracted from them with cer- 
tain -solvents, such as dilute solutions of alkalies at room temperature, or 
water heated to 60 C. Nettling hairs inactivated by either of these measures 
produce no more than a slight redness when rubbed into the skin, and prob- 
ably act then merely as foreign bodies. 
An index for the presence of the irritating substance is found in a peculiar 
reaction which takes place when the active nettling hairs are mingled with a 
drop of blood between a slide and coverglass. This reaction begins about 
the point of the hair, but spreads rapidly so that a large area is involved. 
The first change is the breaking up of the rouleaux of red blood corpuscles. 
The corpuscles then become coarsely crenated ; later are spherical, with slen- 
der spines protruding from the surface; and finally appear perfectly spheri- 
cal and closely packed. If the Irritating substance has been previously 
either inactivated by heat or extracted from the nettling hairs, they no longer 
give this reaction with the fed blood corpuscles. 
"The dermatitis produced by the nettling hairs Is of two types, dependent 
upon the number of these elements penetrating a given area. The severe 
type is usually due to actual contact with the caterpillars; the milder scat- 
tered rash is due to nettling hairs blown in the air and lodging on the skin or 
on the under garments as they hang drying. The pathological process in the 
skin consists of necrosis of the epidermal cells around the nettling hairs, the 
* Second Annual Report of the Superintendent for Suppressing the I Hpsj 
and Brown-tail Moths, Massachusetts, January, 1907, pages 154-168. 
