protein were given to supply this amount, the tissues would be saved. It is found, on the contrary, that nearly twice as much urea is excreted as before. If the quantity of protein be steadily increased, equilibrium is at last established, but not until the amount of nitrogen in the protein given is two and a half times as great as the amount excreted during the starvation period. Additional food at once gives rise to additional waste. The tissues which during the period of scarcity had reduced their oxidation to a minimum become more active at the first hint of returning plenty. This last experiment illustrates a general law. An increase of proteid food within certain limits increases the metabolic activity of the tissues—provokes them to extravagance. It is possible, by adding protein to a mixed diet which sufficed for the maintenance of body-weight and nitrogenous equilibrium, to bring about a nitrogen deficit and to reduce the body-weight. Or, if the body is gaining in weight, owing to the accumulation of fat, the substitution of protein for carbohydrate (weight for weight, since their caloric values are the same) will lead to its reduction. It is difficult to avoid the use of fanciful language in accounting for these results. The animal economy is like an over-careful housekeeper, who, when meat is scarce, doles out porridge also with a thrifty hand. When meat is plentiful she is prodigal with every article of diet. Protein is the most costly of foods. Any indication that it is scarce leads to a shutting-down of activity. On the other hand, no other food is so readily absorbed (unless the digestive organs be protein-sick); none is so quickly incorporated in the bioplasm; none is so easy to decompose. When fed with protein the machinery hums. The insatiable appetite for beef and eggs which overtakes a man of sedentary habits after a long morning in a boat or on a bicycle does not indicate that his muscular tissue is suffering from wear and tear. It does not prove that he is setting free energy by oxidizing proteid food. It shows that he is asking certain tissues which are accustomed to a quiet life to exhibit prodigious energy. They will not shake off their customary sloth unless he stimulates them with sumptuous fare. At the end of a week he finds that proteins are not the best fuel for steady work. If he consumes sufficient to supply all the energy needed by his muscles, he is hampered by a quantity of nitrogenous residues which have to be reduced to urea and eliminated by the kidneys. He goes back approximately to his old regimen, so far as proteins are concerned, and consumes more carbohydrates for the supply of the force which his increased muscular activity demands.