1. The concentration of protein in the serum and plasma of normal dogs is given. Analyses of serum from 38 animals yielded the following averages and standard deviations, (a) for albumin: 3.26 ± 0.48 gm. per cent, (b) for globulin: 2.72 ± 0.76 gm. per cent, and (c) for total protein: 5.98 ± 0.67 gm. per cent. Analyses of plasma from 19 animals showed, (a) for albumin: 3.38 ± 0.38 gm. per cent, (b) for globulin: 2.98 ± 0.55 gm. per cent, and (c) for total protein: 6.36 ± 0.71 gm. per cent.
2. A diet for dogs is described, the feeding of which results in a progressive decline in the concentration of protein in the serum. A composite curve constructed from the findings with 21 animals discloses a rapid initial fall and a slower subsequent decrease in albumin and total protein and an approximately constant level for globulin. The course of the globulin curve was subject to wide variation in separate experiments, both increases and decreases being recorded.
3. With five dogs the nitrogen balance was followed through a total of 42 metabolism periods of approximately 7 days each. The average daily loss of nitrogen was 1.15 gm. Approximate calculations disclose that only 3 or 4 per cent of the nitrogen eliminated is accounted for by the decline in circulating protein, the remainder being represented by loss from the tissues.
4. An episode is described with one dog when, during a period of self-imposed fasting, the serum albumin regenerated to a normal level, apparently at the expense of catabolized tissue protein.
5. The course of serum proteins is described during the recovery which follows interruption of the low protein diet and return to a regime of adequate feeding.
6. A discussion is given of the relationship between tissue proteins and plasma proteins. The data permit one to entertain the hope that a way will be found for stimulating an internal readjustment to provide temporary relief from hypoproteinemia, a way which will depend upon the potential ability of the tissues to provide sufficient protein for the needs of the plasma.