the unsanitary and extremely expensive rat nuisance is so hard to abate. The amino acids that are circulating in the blood stream after every meal are primarily to be used for repairing protoplasmic wastage; also they serve for the manufacture of new protoplasm, provided growth is going on. In theory an adult who is through with all his growth except in the skin and one or two other minor tissues should be able to get along with just the amount of protein which will make good his protoplasmic wastage. Since protein is an expensive food and likely to be hard to get in times of scarcity, the question of how much protein should be eaten is of great practical importance. There are several ways of studying the problem; one is by the actual study of diets to find out how much protein people do habitually eat; another is by finding out how much the daily protoplasmic wastage amounts to. If no more protein is being eaten than is necessary for the protoplasmic wastage, these two figures should be about the same. The way of finding out how much protoplasmic wastage there is is to go on a diet which contains abundant starch and fat for energy supplies, but no protein or amino acids. When one is on that kind of diet he knows that he will not have to burn up any of his own tissues to supply him with the energy for his metabolism; whatever breakdown of protoplasm occurs on such a diet is the natural wastage of the body and not the result of using tissues for fuel, as is the case in complete starvation. It is fairly easy to keep track of the decomposition of protein in the body, because protein contains nitrogen and the nitrogen is given off almost wholly in the waste products that are passed out from the kidneys. By collecting the urine and analyzing it for nitrogen the amount of protoplasmic breakdown in the body can be determined, provided no nitrogen-containing compounds were taken in with the food. Otherwise, of course, one could not be sure that nitrogen appearing in the urine had actually come from the wastage of protoplasm. The fact is that when an average-sized human being goes on a diet which contains no protein, but is ample in other respects, he loses daily from his body about an ounce of protein. This is proven by the occurrence in the urine of an amount of nitrogen which stands for that much protein. The person may be gaining or losing weight meanwhile; if his consumption of fats, starches, and sugars is excessive, he may deposit some fat, in which case he might gain weight in spite of the loss of some of his actual living protoplasm. Usually though, in experiments of this kind, there is a steady loss of weight made up of the ounce of protein and of three or four ounces of water. We have to remember that living protoplasm is three-fourths or more water, so that whenever any protoplasm wastes away, some water will be lost as well as protein. It is a very interesting fact that this protoplasmic wastage goes on