164 GYPSY AND BROWN-TAIL MOTHS. [Jan. 



the nettling hair. This is proved by the failure of the fluid from the 

 caterpillar to produce, when mingled with mammalian blood, any char- 

 acteristic change in the red blood corpuscles. The reaction of the human 

 skin in this instance is much more severe, but, on the other hand, is of 

 much shorter duration than is the case of the lesions produced by the 

 nettling hairs. It is possible that the fluids of other caterpillars, usually 

 regarded as innocuous, would be found equally poisonous if rubbed into 

 excoriations of the skin ; but this was not tried. 



The pathological processes produced by the nettling hairs of the 

 brown-tail moth were studied in both human and animal tissues. 



The reaction of the human skin to the nettling hairs of the brown- 

 tail moth varies greatly with different individuals. "When these hairs 

 are rubbed upon the skin, there is immediately, with most persons, con- 

 siderable itching, and the inoculated area rises up in the course of fifteen 

 or twenty minutes in the form of a wheal, about which there is con- 

 siderable reddening, that changes to white when the skin is stretched. 

 The reaction, however, is not always so prompt to appear. The severest 

 process observed showed nothing for a period of eight hours after the 

 inoculation. The nettling hairs, even when rubbed into the skin of other 

 individuals, produce only slight reddening or perhaps very slight eleva- 

 tion, and practically no discomfort. AVhether or not decreased alka- 

 linity of the blood forms a factor in the insusceptibility of these per- 

 sons is only a matter of conjecture. The blood of all persons and of 

 all laboratory animals thus far tried has reacted in a typical manner 

 to the nettling hairs. , 



The dermatitis as it occurs naturally is of two types, according to the 

 manner of acquisition. If, for instance, a caterpillar is felt crawling 

 over one's neck and is thereupon slapped or crushed and the part after- 

 ward thoroughly rubbed and scratched, a marked local dermatitis de- 

 velops, in which the lesions are confluent. There is a local reddening 

 and thickening of the skin, with the formation of papules or vesicle. 

 as the case may be. A patient in this condition is liable to seek the 

 advice of a physician. On the of her hand, if the nettling hairs are dis- 

 tributed by a breeze to underclothes as they hang drying, the dermatitis 

 which results from wearing these clothes is of the nature of a scattered 

 urticarial rash. The lesions in such a case are in the form of small 

 discrete papules, which, if not scratched, often show at their summit a 

 tiny vesicle filled with clear fluid. They are generally more numerous 

 on parts of the body where the skin is soft. Many persons having such 

 rashes never consult the physician. Warm, mimuv weather aggravates 

 the condition : the reason for this is that the epidermis is then kept moist 

 by perspiration, and. becoming softer, favors the penetration of the 

 nettling hairs. In dry, cool weather the epidermis is less easily pene- 

 trated. 



The duration of this form of dermatitis may be long, on account of 

 repeated inoculations; the individual lesions usually, however, heal in 



