It was shown by Stocks (1950) that the standardized mortality of cancer of the stomach tended to be greater in northern than in southern towns in England. Stocks considered this to be consistent with the hypothesis that gastric cancer depends on an irritant. The only environmental factor which appeared to correlate in any way with the varying incidence of cancer of the stomach was hardness of water, towns with a water supply of moderate hardness tending to have lower rates than towns with soft or very hard water. This correlation was not a very close one. He showed also that the standardized mortality of cancer of the stomach was greater in towns with a low proportion of people of advanced age and in towns with a high proportion of men in unskilled and partly skilled occupations. Stocks did not explore, and apparently did not take into account, any possible genetic difference in the populations which he examined, nor was this possibility mentioned by Legon (1951, 1952) in attempts to correlate the geographical variations in the mortality from gastric cancer with variations in the organic content of the soil.