The chemical composition', of 6 full-term human babies and of newly born mice, rats, rabbits, guineapigs, cats, pigs, and one grey seal, is com pared. The outstanding variable was fat, of which human babies contained 11 to 28 per cent., the seal 9 per cent., guineapigs about 10 per cent. and the remaining species only 1 to 2 per cent. A connection is suggested between the high fat content of these. 3 species and their relatively long gestation periods. Also, the lipaemia occurring in pregnant women and guineapigs, but not in rats or rabbits, may be significant for the fetus. The percentage composition of the newly-born mammals is given also on a fat-free basis, and a number of differences in mineral content are discussed. Mice contained more Zn than other species, even those born covered with hair. The liver of the newly born rabbit contained 84 mg. inorganic Fe per 100 g., 4 times as much as any other species. The pig and guineapig had very little liver Fe, but much Cu; the seal, mouse and kitten had the most Zn. These 3 metals may compete for storage proteins in the liver.-D. Duncan.