Protein, which repairs tissue and also furnishes the substance from which new tissue is made, is used more economically during pregnancy than when the maternal functions are inactive. As a result of this economy the same allowance of protein which is sufficient before conception is sufficient also during pregnancy. This fact has been put in the clearest light by extensive observations made upon animals. Dogs which were not pregnant, for example, have been carefully fed so that their food should contain just enough protein to cover the needs of the body and keep their weight constant. Subsequently, when these animals became pregnant precisely the same amount of protein was fed to them. The result was that they gained in weight, and at the same time the waste products of protein they threw off were notably diminished. Such observations, of which there have been a large number yielding concordant results, may be safely taken to mean that an amount of protein previously satisfactory for the animal is also sufficient for her during pregnancy. We are forced to conclude that protein was used more sparingly in the latter condition--a view which has been repeatedly confirmed with regard to human beings as well as animals. It is found, for example, that an amount of protein competent to meet the needs of a man of a given weight will not only provide for the wants of a woman of equal weight while she is pregnant, but will also leave a surplus sufficient for the growth of the fetus. With regard to the mineral substances, likewise investigations indicate that the "housekeeping" of the body during pregnancy proceeds along unusually economic lines. It is not advisable, therefore, to make any change in the diet with regard to these substances. Attempts have been made to cut down the amount of minerals in the food for the purpose of softening the fetal skeleton. The success sometimes attributed to these efforts is, however, very doubtful, for we know that the mother's tissues will be robbed of minerals for the embryo whenever her food fails to contain them in sufficient amount for her own needs and those of the child. Practically speaking, the mineral content of diet during pregnancy requires no thought, for so long as meat and vegetables are eaten in satisfactory quantity the mineral nutrition will take care of itself.