are closely related to variations in the amount of hæmoglobin. Leichtenstern states that the excess in men of hæmoglobin is 7 per cent. until the tenth year, 8 per cent. between 11 and 50 years, and 5 per cent. after the fiftieth year.[63] Jones states further[64] that the specific gravity is higher in persons of the upper classes and lower in the poorer classes. Observations of boys who were inmates of workhouses gave a mean specific gravity of 1,052.8 and on schoolboys a mean of 1,056, while among the undergraduate students of Cambridge University he found a mean of 1,059.5. Several men of very high specific gravity in the last group had distinguished themselves in athletics. "Workhouse boys are in most cases of poor physique, and one can hardly find a better antithesis than the general type of physique common among the athletic members of such a university as Cambridge."[65] There is no more conclusive evidence of an organic difference between man and woman than these tests of the blood. They permit us to associate a high specific gravity, red corpuscles, plentiful hæmoglobin, and a katabolic constitution. A comparison of the waste products of the body and of the quantity of materials consumed in the metabolic process indicates a relatively larger consumption of energy by man. It is stated that man produces more urine than woman in the following proportion: men, 1,000 to 2,000 grams daily; women, 1,000 to 1,400 grams. As age advances, the amount diminishes absolutely and relatively in proportion to the diminution of the energy of the metabolic process. A table prepared from adults of both sexes, twenty-five years of age, of the average weight of sixty kilograms, shows a larger proportion both of inorganic and organic substances in the urine of men.[66] Milne Edwards has found that the bones of the male are slightly richer in inorganic substances than those of the female.[67]