Nature provides against ignorance of the amount of supply necessary, by enabling the system to carry off a limited amount of surplus food above the bodily requirements. Her capacity in this regard is limited and varies with each individual. Therefore common sense is required in deciding for oneself the amount of food which will aid, and not hinder Nature in her processes. Without doubt many eat more food than the system requires, and when it is overloaded they do not take the pains to burn up and eliminate the excess through exercise and oxygen. On the other hand, this theory of overeating has been so long discussed that many have not eaten sufficient food and their bodies are undernourished. Many, also, from lack of exercise, hence lack of demand of the body for food, have supposed this lack of appetite to be Nature’s call “Enough”; inertia has resulted and waste remains in the body. They have failed to exercise sufficiently to create a demand for food. It is thus undernourished because sufficient new building material has not been supplied. The relief from this condition is exercise and deep breathing so that Nature removes the waste and calls for fresh building material. Many others, through mental and physical activity, burn up much fuel and the result is the body does not store up sufficient fat for a reserve, or for beauty and comfort. The nerves require a certain amount of fat for their protection. People of this type should take a more full and sometimes a more varied diet, particularly more liquid, and should not fail in daily exercise and deep breathing. Each individual should know, approximately, the chemical constituents and the proportion of these constituents in normal blood, because from the elements in the blood, the tissues are constructed. If certain elements are lacking, the foods containing these elements in largest proportions should be supplied until the blood no longer shows the deficiency. This is Nature’s method of correction. The variations in the blood can be known only by chemical analyses and until physicians have access to chemical laboratories the giving of drugs cannot be a science. Each meal, or each day’s food, may not contain the amount of protein or of fuel ingredients necessary for that day’s work and resupply, but the body is continually storing material, and this reserve is constantly being drawn on to provide any element which may be lacking in that day’s supply. Thus, an excess or a deficiency one day may be adjusted the next. Healthful nourishment requires that the balance, as a whole, be kept and that a deficiency or oversupply be not continued for too long. The distinct steps in anabolism and the effect of oxygen on assimilation are discussed in the following pages. _DIGESTION_