The intake and excretion of calorific constituents of milk by babies.

I . The intake and excretion of energy, total nitrogen, fat and carbohydrate by twenty baby boys aged about a fortnight were measured over 3 days. 2. Ten of the babies received breast milk which had been expressed from their mothers, the remaining ten received one of two preparations based on dried cow’s milk, with either lactose or sucrose added. 3 . The intake of energy, protein and carbohydrate was greater in the ten babies receiving the cow’s milk preparations. 4. The urinary excretion and retention of N was greater in the babies fed on the cow’s milk preparations. 5. The absolute excretion of N in the faeces was simiIar whatever the diet, but the excretion of fat was less and the excretion of carbohydrate greater for babies having breast milk. 6 . The ca1orie:N ratio in the urine was 5.8 kcal/g urinary N in those receiving breast milk and 4.8 kcal/g N in those fed on the cow’s milk preparations. The value for the adult is 7.9. 7. Calorie conversion factors have been calculated which are more appropriate for milk diets for babies than the factors of Atwater which were designed for mixed diets for adults.