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Abbott Laboratories, North Chicago, Illinois
By employing suitably prepared dogs, the minimum amount of a protein required to maintain nitrogen balance (MPN value) was determined.
The MPN values of casein, crude fibrin, and pharmaceutical grade fibrin were found to be, respectively, 140160, 70 and 80100 mg N/kg/day.
Fortification of casein with cysteine reduced the MPN value to 80100 mg N/kg/day. When both cysteine and methionine were added to casein in sufficient amounts, the MPN value fell to 6070 mg N/kg/day.
The MPN value for lactalbumin was not determined, but it maintained nitrogen balance when given at the rate of 100 mg of lactalbumin nitrogen/kg/day.
2 Present address: Bristol Laboratories, Inc., P.O. Box 657, Syracuse, N. Y.
Manuscript received 27 February 1946.