Rhus vernicifera contains urusiol in the latex, but many other species of Anacardiaceae contain similar substances. These two varieties are extremely alike in their microchemical characters and show indentical colour reactions with the reagent mentioned below. Thus we can easily prove the existence of these substances in a latex, obtained by piercing the leaf or stem, by the use of the microchemical method of testing. The method is as follows : first add absolute alchohol to the latex on a slide glass, and next add 15-50 % nitric acid to the portion impregnated. with alchohol. Its colour will then change to bright red or red after 1-2 seconds. Caustic potash also produces good results. Even with a 5-10 % solution it shows a deep green colour very soon in the portion treated with alchohol. Both 1-5 % copper acetate solution and 1-5 % ferric chloride react as well as caustic potash, the former quickly turning the portion treated with alcohol purple-black, and the latter turning it black. If 15-52 % nitric acid is added to the latex without alchohol it will soon turn red-brown, but a weak solution of this acid is slow in its reaction. A 20 % solution takes from 1 to 2 minutes for the colour reaction, and a 35% solutiom from 5 to 7 seconds. But this nitric acid seems to act upon the other substances in the latex besides the urusiol or similar substance, and colour reaction of the latex is somewhat different from that when alchohol is present. On the other hand, when a solution of caustic potash, copper acetate, and ferric chloride reacts directly in the Iatex without alcohol, the reaction colours appear sharply, even with a weak solution, and there is no difference from the colours which are shown when alcohol has been added. We can judge by this microchemical method if each species of Anacardiaceae is poisonous or not, and also whether the latex of each species is of value for such purpose as the manufacture of paints. So we find that these questions depend principally upon whether the latext contains urusiol or simillar substances or not.