We may next profitably consider the effect of a pure proteid diet--such as lean meat free from fat--on the output of nitrogen. In studying this problem, we at once meet with several important and surprising facts. First, we are led to see that, strange as it may seem, every addition of proteid to the diet results in an increased excretion of nitrogen. In other words, increase of proteid income is followed at once by an increase in the metabolism of proteid, with a corresponding outgo of nitrogen. The hungry or fasting man with his income entirely cut off, and consequently suffering from a heavy drain upon his capital stock, would be expected, when suddenly supplied with fresh capital in the form of meat or other kind of proteid food, to hold on firmly to this all-important foodstuff; but such is not the case. It is impossible, for example, to establish nitrogen equilibrium by an income of proteid equal to what the individual during fasting is found to metabolize. As stated by another, “It is one of the cardinal laws of proteid metabolism that the store of nitrogenous substances in the body is not increased by, or not in proportion to, an increase in the nitrogen intake.” The principle is well illustrated in the fasting experiment just described. On the fifth day of fasting, the nitrogen output amounted to 11.4 grams. On the day following, the man took 35.6 grams of nitrogen in the form of proteid, while the excretion of nitrogen for that day rose to 26.8 grams. In other words, although deprived of all proteid income for five days, and during that period drawing entirely upon his proteid capital, the man was wholly unable to avail himself of the proteid so abundantly supplied at the close of the fast and make good the losses of the preceding days; only a small proportion of the proteid income could be retained. If a dog fed on a definite quantity of meat suddenly has his proteid income increased, there is at once an acceleration of proteid metabolism, and a corresponding increase in the output of nitrogen. Addition of still more proteid to his income is followed by an accumulation of a portion of the proteid; but this tends to decrease gradually, while there is a corresponding daily increase in the excretion of nitrogen. In this manner, there finally results a condition of nitrogenous equilibrium or nitrogen balance.