In an investigation of the rôle of 1:2:5:6–dibenzanthracene in the production of tumors Chalmers (1934) examined, spectrographically, tissues of fowls that had received injections of this hydrocarbon dissolved in fat. Similar spectrographic studies, on mouse tissues, have been carried on in this laboratory and obstacles similar to those reported by Chalmers have been encountered. Chalmers found that some extracts contained substances which showed “intense absorption in the ultraviolet.” Such substances would mask the dibenzanthracene spectrum; consequently the spectrographic analysis of those extracts was being held in abeyance, Chalmers stated, until the interfering substances could be removed. He found that extracts of tissue into which dibenzanthracene had been injected two years previously showed no selective absorption even though the extracts were concentrated “to the point of general absorption in the ultraviolet.” Chalmers then determined, on successive days, the quantity of dibenzanthracene remaining after injection and found that most of the hydrocarbon disappears from the site of injection within a week. Berenblum and Kendal (1934) injected a colloidal aqueous preparation of dibenzanthracene into the breast muscle of the fowl and, by means of the fluorescence spectrum, examined the muscle extracts for the presence of the hydrocarbon. The method was said to be sensitive to 0.02 mg. These investigators stated: “Since each of the 7 birds initially received 0.6 mg. of dibenzanthracene, while less than 0.02 mg. was present in the breast muscle at the end of the experiment, most of the dibenzanthracene must have disappeared from the site of injection during the course of the experiment.”