Foreign plasma protein (horse) introduced parenterally into the protein fasting dog is not utilized in the body economy. Its fate appears to be disintegration and elimination as excess urinary nitrogen. This is totally different from the fate of dog plasma protein under similar conditions.

Dog hemoglobin given parenterally to the protein fasting dog is not utilized as is dog plasma protein to keep the animal in nitrogen equilibrium but the globin is largely broken down and discarded as excess urinary nitrogen. A small part of the injected hemoglobin is probably utilized to maintain the red cell concentration in the blood at high levels.

Dog plasma given parenterally in a protein fasting dog will maintain the dog in nitrogen equilibrium and there is no surplus nitrogen elimination in the after periods. It is apparent that the introduced plasma protein is utilized efficiently in body metabolism to replace or repair tissue protein. It is suggested that although this is an emergency reaction the same reactions may go on in normal internal metabolism. The observation that foreign plasma and dog hemoglobin cannot be utilized when given parenterally actually strengthens this last argument for a normal contribution from plasma proteins to body proteins.

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