Sex Differences in the Requirements of Certain Food Factors.*

T H E adult male in any species is generally recognised as being a larger and heavier animal than the adult female. Donaldson gives the weight of a male rat as 279.9 gms. and of the female as 230.4 gms. at 365 days, presumably fully grown. It also appears to be accepted that the metabolism of the male is different from that of the female. Possibly this is quite correct, for the functions of the two are widely divergent. Mitchell points out that the biological value of proteins for growth is probably quite a different problem from the biological value of protein for maintenance, and further that the conditions of gestation and lactation also call for separate investigation. In these respects the function of the female is different from that of the male, and therefore it might well be expected that the requirements of the two sexes should differ. In spite of this, many nutrition workers use only one sex for their experiments, and there are no available data giving the separate requirements of each sex. Osborne and Mendel describe some very interesting experiments in which they endeavoured to find the daily dosage of vitamin B needed to keep a rat in health and to provide for normal growth. These observers, unfortunately, used a large majority of male