LONDON Royal Society, February 14. G. BARRY, J. W. COOK, G. A. D. HASLEWOOD, C. L. HEWETT, I. HIEGER and E. L. KENNAWAY: The production of cancer by pure hydrocarbons (3). Tests for cancer-producing activity on the skin of mice have been carried out with a number of pure compounds of known molecular structure, most of which have been polycyclic aromatic hydrocarbons. In all, some 140 different compounds have now been tested. Of these, 69 are related to 1: 2-benzanthracene and 25 of them have given positive results. 1: 2-benzanthracene itself has very little carcinogenic activity, but such activity is shown by derivatives in which substituents (saturated alkyl groups or additional rings) are attached to positions 5 or 6, or both. The most active so far encountered is methylcholanthrene, a hydrocarbon which was obtained by simple chemical means from the deoxycholic acid of bile. In this way a direct relationship has been established between the carcinogenic compounds and some normal constituents of the body. Of 71 compounds not related to 1: 2-benzanthracene, 65 have given completely negative results. Of the 6 compounds which gave positive results, only 3: 4-benzphenanthrene ahd considerable activity. The remaining 5 compounds gave only 10 tumours (2 epitheliomas and 8 papillo-mas) in 360 mice. By way of contrast the 25 carcinogenic compounds related to 1: 2-benzanthracene gave 437 tumours (335 epitheliomas and 102 papillomas) in 1,220 mice. C. H. WADDINGTON, J. NEEDHAM, W. W. NOWINSKI and R. LEMBERG: Studies on the nature of the amphibian organisation centre. (1) Chemical properties of the evocator. An evocator, that is, a substance capable of causing the ectoderm of the amphibian gastrula (Triton spp., axolotl) to differentiate into neural tissue, has been obtained in ether extracts of whole newt bodies and of mammalian liver. The active substance is present in the unsaponifiable fraction, and in the part of that fraction precipitable with digitonin. It comes out with the cholesterol if the unsaponifiable fraction is allowed to crystallise from alcohol in the cold, and is probably of a sterol-like nature. An active ether -soluble substance, which is also precipitable with digitonin, has been isolated from crude preparations of glycogen. The whole of the evocating activity of glycogen may be due to the admixture of this substance. C. H. WADDINGTON and D. M. NEED-HAM: Studies on the nature of the amphibian organisation centre. (2) Induction by synthetic sterol-like substances. Certain synthetic hydrocarbons have been implanted into young amphibian gastrulse. Inductions of neural tissue have been performed by 1: 9-dimethylphenanthrene, 9: 10-dihydroxy-9: 10-di-n-butyl-9: 10-dihydro-l: 2: 5: 6-dibenzanthracene, and 1:2:5: 6-dibenzanthracene. The first two of these are oestrogenic and the third carcinogenic. There is therefore probably a group of evocating substances which overlaps with the group of oastrogenic and carcinogenic substances. This provides the first satisfactory evidence that more than one substance is capable of evocating, and suggests that the naturally occurring evocator is a sterol-like substance.