When the protein consumption of normal human individuals is increased from 0.5, to 1.5, to 2.5 gm. of protein per kilo body weight, the specific gravity of the plasma rises and the hematocrit value falls.

The analysis of variance demonstrates that the change in protein consumption is a significant but minor factor in determining the total variability of the observations.

When albino rats were given diets containing a small, a moderate, and a large amount of protein, there was an increase in serum protein concentration but no change in hematocrit value.

During the period over which the most rapid changes in rate of urea excretion and serum urea concentration occurred as normal human individuals passed from a 2.5 to an 0.1 gm. of protein per kilo body weight consumption, there was no change in serum protein concentration.

Over a 5 day period during which a diet that was adequate in calories but almost wholly devoid of protein was taken, the serum protein concentration of normal individuals steadily rose. This was associated with a slight increase in hematocrit value but no change in blood or plasma volume.

The protein effect is one of the minor factors that contribute to the variability of serum protein and hematocrit measurements in normal individuals.

The general conclusion is reached that we shall have to measure the rate at which red cells and protein enter and leave the circulating blood stream before we can hope to comprehend the mechanism of the protein effect.

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