1907.] PUBLIC DOCUMENT No. 73. 161 



the red blood corpuscles, and when even rubbed into the skin now failed 

 to produce a typical dermatitis, but only a slight redness, which \\;is 

 scarcely discernible, and which was probably comparable with that pro- 

 duced by the penetration of the epidermis by minute foreign bodies, 

 such as particles of glass or the barbed hairs of other caterpillars. The 

 degree of heating does not, in this instance, affect the structural in- 

 tegrity of the nettling hairs, for they appear unchanged even after 

 baking an hour at 150 C. 



The experiment of heating the nettling hairs at various temperatures 

 proves conclusively that their action upon the skin is not purely a 

 mechanical one, but that it depends upon the presence of a chemical 

 substance which is destroyed at high temperatures. The failure of the 

 nettling hairs, after being heated to 115 C., to give the characteristic 

 reaction with red blood corpuscles, together with the fact that they no 

 longer produce the typical dermatitis, suggested the possibility that this 

 peculiar reaction might serve as an index to their toxicity. This was 

 put to the test in subsequent experiments, and this inference has been 

 borne out. 



In order to determine the solubility of the irritating substance con- 

 veyed by the nettling hairs, the effect of various solvents was tried both 

 at room temperature and heated. For the time being the presence of 

 the poison in the solvent was disregarded, and the reaction of the 

 nettling hairs with the red blood corpuscles and upon the skin was de- 

 termined after they had been placed under the influence of the solvent. 

 By so doing it was believed that it would be possible to estimate at 

 least the relative degrees of solubility of the irritating substance. 



Treated with alcohol, acetone, chloroform and ether, the nettling hairs 

 remained active both as regards the test with red blood corpuscles and 

 the inoculation of the skin, whether boiled for a short time or kept for 

 days at room temperature. The nettling hairs remained active after 

 being boiled in pyridin, which boils at a temperature between 106 and 

 108 C. Kept in pure glycerine or in equal parts of glycerine and dis- 

 tilled water for several days, the nettling hairs remained active. They 

 were also active after heating at 110 C. in pure glycerine, but after 

 heating at 115 C. they failed to react. As this was the approximate 

 temperature at which they were inactivated by dry heat, it seems cer- 

 tain that the poison is destroyed at this temperature. The nettling 

 hairs also remained active when kept for several days in glacial acetic 

 acid, in Y 2 per cent, acetic, and in both 1 per cent, and -jL per cent, 

 aqueous solutions of hydrochloric acid. The reaction with the red 

 blood corpuscles was delayed for a short time after the soaking in acids, 

 but afterward went on undiminished. This retarding of the reaction 

 is probably due to the fact that several moments must elapse before 

 the acidity of the hairs is neutralized by the blood in which they were 

 placed. The retardation is more pronounced after strong than after 

 weak acid solutions, but if the hairs are subsequently thoroughly washed 



