The work we are reporting here grew out of an interest in the results published by Landsteiner and his collaborators in the Journal of Experimental 2~ledicine between 1935 and I941 as "Studies on the Sensitization of Animals with Simple Chemical Compounds."
It seemed of interest to extend these methods to two substances which are of importance as war gases, namely phenarsazine chloride (DM) and chloroacetophenone (CN).
Phenarsazine Chloride.--A I per cent. solution of DM was prepared by dissolving the compound in a mixture of equal parts of dibutyl phthalate and olive oil. Each of a group of six guinea pigs was shaved on the side and five of them were treated by spreading a drop of the solution with a glass rod over an area about the size of a quarter; the corresponding area of the sixth pig was spread with a drop of the solvent mixture. This treatment was repeated at the same sites for 21 times at three day intervals. Two weeks after the last treatment, o.I ml. of a DM-albumin complex was injected intracutaneously at another site in each of the six animals. During the following 72 hours, no differences between the reactions of the experimental and control animals were observed, and it was concluded that no sensitization had taken place which could be detected by this method.
In a second experiment, a 2 per cent. solution of DM in ethyleneglycol monomethylether ("cellusolve") was used. In this solvent the DM does not cloud and precipitate as it does in the first solution. The spreading was carried out as before in a group of five guinea pigs and one control for I3 times at three day intervals, and two weeks after the last treatment a test was made by spreading a drop of the material at another site. No reaction was observed in any of the animals, nor