When blood plasma proteins are depleted by bleeding with return of the washed red cells (plasmapheresis) it is possible to bring dogs to a steady state of hypoproteinemia and a uniform plasma protein production on a basal diet limited in protein. Such dogs are clinically normal but have a lowered resistance to infection and certain intoxications.

Casein digests given by vein or subcutaneously to such plasma depleted dogs are effective in promoting abundant new plasma protein production. Casein digest L by vein is equivalent to whole liver of like protein equivalence by mouth. The ratio of new plasma protein production to protein intake is 20 to 25 per cent in both instances.

Casein digest L by vein gives the same response in plasma protein output as the same digest by mouth. Protein digest X by vein requires addition of tryptophane and cysteine to be effective in plasma protein production. The added cysteine sulfur is more than 95 per cent retained by the dog.

The speed of digest injection has no effect on its utilization, within the range tested.

Casein digest L given by vein to non-depleted dogs is less well utilized than in dogs depleted of plasma protein.

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