THE NEW SOUTH WALES INSTITUTE OF PSYCHIATRY

the year appeared to be the critical level. In West Africa, most of which lies below 3000 feet, and where there are not the extremes of altitude within a limited compass found in Central and East Africa, variations in the incidence of the tumour were, however, still apparent. But here there are marked variations in rainfall, and consequently in the pattern of the vegetation in different regions. In the dry parts, the tumour was practically unheard of, but it was fairly commonly seen in the more verdant areas. There was some evidence that local epidemics of the tumour arose, a failure of the rains leading to a dearth of cases and a wet season being followed by a fresh outbreak. It thus seemed that humidity, related as it is to the local patterns of vegetation, as well as temperature, was a controlling factor. In no region of Africa did the incidence of the tumour have the slightest relationship to the relative population densities.