When blood plasma proteins are depleted by bleeding with return of the washed red blood cells (plasmapheresis) it is possible to bring dogs to a steady state of hypoproteinemia and a uniform plasma protein production on a basal low protein diet. These dogs are clinically normal but their resistance to infection is distinctly below normal. Introduction of variables into this standardized existence gives information relative to plasma protein production.

Plasma protein production under these conditions with a plasma protein concentration of 3.5 to 4.2 gm. per cent is relatively constant. As the plasma protein concentration rises the plasma protein removed falls rapidly (Table 1). At 4.6 gm. per cent the protein removed is less than 50 per cent of the amount removed at a plasma protein level of 4.0 gm. per cent.

Cystine appears to be an important amino acid for plasma protein formation. This shows in Table 2 and is supported by data coming from published experiments.

These experiments related to the factors which control plasma protein production bear on the problems of shock, hemorrhage, and protein wastage and their treatment by plasma injections which hold the attention of surgeons and physiologists at the moment.

Again we would emphasize the fluidity of body protein including plasma protein—an ebb and flow between protein depots and plasma protein—a "dynamic equilibrium" of body protein. A discussion of the passage of large protein molecules through cell borders is submitted.

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