Part I . Concentration of the Active Substance. By I. HIEGER. THE first experimental production of cancer by the products of distillation of coal was achieved in 1915 by Yamagiwa and Ichikawa (Mitteil. med. Facultit, kaiser. Univ. Tokyo, 1915, 15, 295), and the first enquiry into the chemical basis of tar cancer was that of Bloch and Dreifuss (Schweiz. med. Woch., 1921, 2, 1033), who concluded from their observations that the substance responsible must be a high-boiling, neutral, non-nitrogenous compound which forms a stable picrate. The production of strongly carcinogenic tars by pyrolysis of isoprene or acetylene in a current of hydrogen (Kennaway, J . Path. Bact., 1924, 27, 233; Brit. Med. J., 1925, ii, 1) showed that the agent present in these tars must be a hydrocarbon. A large number of known constituents of fractions of coal and other tars boiling above 270" were tested in this Institute with negative results. The use of the fluorescence spectrum, first applied to this problem by Mayneord in 1927, was continued by the present author (Biochem. J., 1930, 24, 505) with observations on a specific fluorescence spectrum (bands at 4O00, 4180, 44OOA.) common to the tars and mineral oils which produce cancer of the skin either as an industrial disease or i n animal experiments.These spectra suggested an attempt to isolate the fluorescing substance, whether this were the cancer-producing factor itself or some substance which closely accompanies this factor. The results of spectrographic and biological tests have now proved to be in complete agreement. Thus the preparations derived from pitch by a variety of solvent extraction methods, the fractions separated by formation of picrates, distillation and crystallisation, and finally the hydrocarbon (1 : 2-benzpyrene) have proved carcinogenic and have given in each case the fluorescence spectrum with bands at 4000,4180,4400 A. The treatment of pitch described here has yielded fractions which are f a r superior to pitch as cancer-producing agents and at the same time possess the specific fluorescence spectrum in an enhanced degree.Hence the fluorescence test can predict the behaviour of fractions of pitch when tested on animals, although it must be pointed out that certain cancer-producing hydrocarbons prepared synthetically (e.g., 1 : 2 : 5 : 64ibenzanthracene) have fluorescence spectra different from those of active pitch fractions. EXPERIMENTAL.Two tons of a medium soft pitch (see fluorescence spectrum I) which was shown to be cancer-producing (see below) were distilled from a cast-iron retort. The distillate above 510" (thermometer in liquid) resembled the deep red glassy distillate of pitch which was found some years ago to be carcinogenic (Kennaway, Brit. Med. J., 1924, i, 564). The fraction, b.p. 500-510", resembled very soft pitch and was much more sol. in ordinary solvents than the fraction, b. p. above 510". A fraction with the same physical characteristics distilled at 475-500"(pyrometer instead of thermometer); yield, about 5% of the charge of pitch. From t...

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Cytomegalovirus colitis in the immunocompetent patient is an unusual clinical entity. We describe a patient with life-threatening cytomegalovirus colitis in the absence of immune deficiency and review the medical literature available on this topic.

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