The proteins and protein-bound carbohydrates of the serum of the developing pig.

1. The concentrations of total nitrogen, hexosamine and protein-bound hexose and the amounts of these constituents precipitated by trichloroacetic acid were determined in the serum of pigs at various ages from 57 days after copulation to 42 days after birth. The concentrations of the same constituents were also determined in the serum of mature pigs. 2. A rise in the concentrations of total nitrogen, hexosamine and protein-bound hexose between 90 days' gestation and term was entirely due to material soluble in trichloroacetic acid. This material disappeared from the serum by 7 days after birth. 3. Electrophoresis of the serum proteins showed that the concentration of alpha(1)-globulin fell steadily during gestation, being lower at term than at 57 days' gestation. No alpha(1)-globulin was detected at 7 days of age. 4. It was concluded that high values for non-protein nitrogen in the serum of newborn piglets, determined after precipitation of the proteins with trichloroacetic acid, is largely due to the presence of one or more mucoproteins and not to alpha(1)-globulin. 5. The protein migrating in the alpha(1)-globulin position is possibly a foetal protein of the fetuin type.