150 ALEXANDER VON HUMBOLDT. 



Pictet, Van Mons, Fourcroy, Loder, &c., as well as in various 

 treatises in Grren's, Crell's, Millin's, and other periodicals. 



In June, 1795, Humboldt writes to Blumenbach: <I can only 

 describe to you here one experiment. I applied two blisters to 

 my back, each of the size of a crown-piece, and covering respec- 

 tively the trapezius and deltoid muscles : I lay meanwhile flat 

 upon my stomach. When the blisters were cut, and contact 

 made with zinc and silver, I experienced a sharp pain, which 

 was so severe that the trapezius muscle swelled considerably, 

 and the quivering was communicated upwards to the base of 

 the skull and the spinous processes of the vertebra?. Contact 

 with silver produced three or four single throbbings which I 

 could clearly separate. Frogs placed upon my back were ob- 

 served to hop ; when the nerve was not in immediate con- 

 tact with the zinc, but separated from it by half an inch, and 

 the silver only in contact, my wound served as a conductor, 

 and I then felt nothing. Hitherto my right shoulder was the 

 one principally affected. It gave me considerable pain, and 

 the lymphatic serous humour produced in some quantity by the 

 irritation was of a red colour, and, as in the case of bad sores, 

 was so acrid as to produce excoriation in places where it ran down 

 the back. The phenomenon was of too striking a nature not 

 to be repeated. The wound on my left shoulder was still filled 

 with a colourless watery discharge, and I caused the nerves to 

 be strongly excited in that wound also by the action of the 

 metals. Four minutes sufficed to produce a similar amount of 

 pain and inflammation with the same redness and excoriation 

 of the parts. After being washed, the back looked for many 

 hours like that of a man who had been running the gauntlet.' 



On his return from Italy and Switzerland, Humboldt insti- 

 tuted in December, 1795, a repetition of his former experiments, 

 and supplemented them by an additional series, in consequence 

 of his interviews with Volta and Scarpa, both of whom he had 

 visited when at Pavia and on Lake Como. 



He thus describes them : ' Dr. Schallern experimented upon 

 my back for fully three-quarters of an hour. The painful pro- 

 some notes to my book. He is so eager about it, that he has already sent 

 translations of certain portions to Banks in London.' 



