Given healthy dogs, fed abundant iron and protein-free or low protein diets, with sustained anemia due to bleeding, we can study the capacity of these animals to produce simultaneously new hemoglobin and plasma protein.

The reserve stores of blood protein producing materials in this way are very largely depleted, and levels of 6 to 8 gm. per cent for hemoglobin and 4 to 5 gm. per cent for plasma protein can be maintained for considerable periods of time. These dogs are very susceptible to infection and to injury by many poisons.

Under such conditions, these anemic and hypoproteinemic dogs will use very efficiently a variety of digests (serum, hemoglobin, and casein) and the growth mixture (Rose) of pure amino acids. Nitrogen balance is maintained and considerable new blood proteins are produced.

Dog plasma by vein is used freely in these doubly depleted dogs to make new hemoglobin in abundance (Table 1). Serum digests by vein are well utilized to make new hemoglobin and plasma protein in the same dogs (Table 1). Serum digests by mouth are effectively used to make new blood proteins (Table 5).

Dog or sheep hemoglobin given in large amounts intraperitoneally are remarkably well utilized to form hemoglobin and plasma protein (Table 6). It must be obvious that the globin of the hemoglobin is saved in these protein-depleted dogs and used to make large amounts of hemoglobin and plasma protein.

Hemoglobin digests are also well utilized whether given by mouth (Table 7) or by vein (Table 8) and liberal amounts of plasma protein are manufactured from digests presumably ideally suited for hemoglobin production.

Casein digests are well used (Table 8) and form as much new plasma protein as any material tested—even serum digests.

Amino acid mixtures are of especial interest. The growth mixture of 10 amino acids (Rose) is well utilized by mouth or by vein and favors new hemoglobin production more than any material tested (Table 2). Cystine replacing methionine in the amino acid mixture increases the plasma protein—hemoglobin output ratio, that is it favors plasma protein production.

Digests of various sorts and amino acid mixtures or combinations of digests and amino acid mixtures can be used rapidly and effectively to build new hemoglobin or plasma protein, to maintain nitrogen equilibrium, and to replete reserve protein stores. These experiments point to clinical problems.

The unexplained preference given to hemoglobin production in these hypoproteinemic dogs is observed under all conditions, even when whole plasma or serum digests are given by vein. In general, 2 to 4 gm. of hemoglobin are formed for every gram of plasma protein.

This all adds up to a remarkable fluidity in the use of plasma protein or hemoglobin which can contribute directly to the body protein pool from which are evolved, without waste of nitrogen, the needed proteins, whether hemoglobin, plasma protein, or tissue proteins.

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