1. The addition to the Nairobi prison diet of either a mineral supplement (closely reproducing in composition the ash of cows' milk) or of a small dose of cod-liver oil, or a combination of these two, produced in adult African prisoners a distinct improvement in body weight.
2. Similarly an addition of olive oil and iodine produced a like effect but less in degree. The significance of this will require further investigation.
3. Evidence is adduced which suggests that one of the most important constituents of this soluble mineral mixture is calcium. Thus:
(a) The prison diet would appear on the basis of previous work to be deficient in the absolute amount of calcium present, nor does it seem rich in vitamins A and D. (In this connection it seems apposite to mention that cases of “night blindness” have frequently been reported.)
(b) The blood calcium of the 42 experimental subjects was initially at a low normal level.
(c) In the groups receiving the mineral mixture and/or cod-liver oil (which is a recognised calcium absorption promoting agent) the level of the blood calcium was invariably raised.
(d) As indicated above, the body weights in these groups increased. There appears to be, further, a certain amount of correlation between the increase in body weight and that of the blood calcium level.
(e) Balance experiments show that given favourable conditions (i.e. the addition of the mineral mixture alone or along with cod-liver oil) calcium will be absorbed in amount considerably in excess of that absorbed from the basal diet alone.
4. In the course of the work some evidence has emerged that certain other factors, e.g. intestinal parasites and minimum temperature, may respectively influence the blood calcium level and the body weight increase. Should these prove in future work to be real influences they would not vitiate our present conclusions.