Again, an animal brought into nitrogen equilibrium by excessive proteid feeding, if suddenly given a small amount of meat per day, tends to put out nitrogen from its own tissues. This tissue loss, however, decreases slowly, and eventually the animal is quite likely to re-establish nitrogen equilibrium at a lower level. There is, in other words, a strong tendency for the body to pass into a condition of nitrogen balance under different conditions of proteid feeding, even after a long period of nitrogen loss and with an abundance of proteid in the intake. The starving body, as we have seen, cannot make use of all the nitrogen fed, although we can well conceive its great need for all the proteid available. A certain amount of the proteid fed, or its contained nitrogen, is at once passed out of the body and lost, even though the organism be gasping, as it were, for proteid to make good the drain incidental to long fasting. A recent writer[26] has suggested that some explanation for these anomalies may be found in the supposition “that a long succession of generations in the past, which have lived from choice or necessity on a diet rich in proteids, have handed down to us, as an inheritance, a constitution in which arrangements exist for the removal of nitrogen from a considerable part of this proteid. The fact that the amount of proteid taken is re-adjusted to suit the actual needs of the body, though it makes these arrangements unnecessary, will not necessarily remove them. The denitrifying enzyme, which has been trained to keep guard over the entrances by which nitrogenous substances are admitted into the body, will continue to levy its toll of nitrogen, even when the amount of proteid presented to it is no more than the tissues which it serves actually require.” [26] Leathes: Problems in Animal Metabolism. Philadelphia, 1906, p. 157. As an illustration of how the body behaves with a low nitrogen intake followed by a sudden increase in the income of proteid, some data from an experiment performed by Sivén[27] on himself may be cited: [27] Sivén: Zur Kenntniss des Stoffwechsels beim erwachsenen Menschen, mit besonderer Berücksichtigung des Eiweissbedarfs. Skandinavisches Archiv für Physiologie, Band 11, p. 308.