50 
Poisonous Arthropods 
V 
w 
that if the nettling hairs are mingled with blood, they immediately 
produce a change in the red corpuscles. These at once become 
coarsely crenated, and the 
roleaux are broken up in the 
vicinity of the hair (fig. 37 b). 
The corpuscles decrease in 
size, the coarse crenations 
are transformed into slender 
spines which rapidly disap¬ 
pear, leaving the corpuscles 
in the form of spheres, the 
light refraction of which con¬ 
trasts them sharply with the 
normal corpuscles. The 
reaction always begins at the 
(a) Ordinary hairs and three poison hairs of sub- . . , . , r ., , • 
dorsal and lateral tubercles of the larva of the basal Sharp pOUlt OI the hair. 
browntail moth. Drawing by Miss Kephart. R ^ ^ produced by 
purely mechanical means, such as the mingling of minute par¬ 
ticles of glass wool, the barbed hairs of a tussock moth, or the other 
coarser hairs of the brown-tail, with the blood. 
The question of the source of the poison has been studied in our 
laboratory by Miss Cornelia 
37. 
Kephart. She first confirmed 
Dr. Tyzzer’s general results 
and then studied carefully fixed 
specimens of the larvae to 
determine the distribution of 
the hairs and their relation to 
the underlying tissues. 
The poison hairs (fig. 37), 
are found on the subdorsal 
and lateral tubercles (fig. 38), 
in bunches of from three to 
twelve on the minute papillae 
with which the tubercles are 
thickly covered. The under¬ 
lying hypodermis is very 
greatly thickened, the cells 
being three or four times the length of the ordinary hypodcrmal 
cells and being closely crowded together. Instead of a pore canal 
37. 
(6) Effect of the poison on the blood cor¬ 
puscles of man. After Tyzzer. 
