The value of gelatin as an article of diet is of interest in this connection. Gelatin is not, strictly speaking, a protein, and it cannot be built up into the tissues. It does not prevent, nor even delay, starvation. Yet up to a certain point it can be used as a substitute for proteid food. In the observation just referred to, protein might be withdrawn at any stage, without disturbing nitrogenous equilibrium, by substituting about 2 grammes of gelatin for every gramme of protein withdrawn. It spares protein, although it does not take its place. It is said that the minimum of protein necessary for the maintenance of nitrogenous equilibrium may be reduced to about one-half by the substitution of gelatin. This has been interpreted as indicating that when we have reduced the oxidation of nitrogenous substance to its smallest amount the nitrogen comes from two sources in about equal proportions—(_a_) the bioplasm; (_b_) the food-proteins in contact with it. It is inferred that gelatin, although it cannot be built up into bioplasm, may take the place of proteins present in the cell-juice. It appears to be impossible to starve the cell until it consists of a bioplasm framework bathed in nitrogen-free cell-juice. As the non-living proteins of cell-juice are removed, they are, if no nitrogenous food be given, renewed by the breaking down of bioplasm. When gelatin is absorbed, it takes its place in the cell-juice, and the breaking down of bioplasm is no longer necessary. When digestion is impaired, or vitality lowered, decoctions of meat which contain extractives of low calorific value, useless, without synthesis (_cf._ p. 144), for the purposes of tissue-repair, may to a certain extent save tissue-waste. In the same way, gelatin, which is very rapidly digested in the stomach, may cover the consumption of proteins, although it cannot take their place. To sum up: The requisite daily income of energy must come from both nitrogenous and non-nitrogenous food. It is impossible to reduce the nitrogenous factor below a certain minimum. From this minimum upwards, until a certain level is reached, every additional unit of nitrogenous food enables the system to dispense with more than its equivalent of non-nitrogenous food. When the proper balance of foods is attained, there is no waste either of labour involved in digestion, or of labour involved in metabolism and excretion. =The Liver.=—The liver weighs from 3 to 3½ pounds. It lies beneath the diaphragm, more on the right side than on the left. Its posterior border, which rests against the last three ribs (separated from them by the diaphragm), is about 3 inches thick. Its anterior border is thin, and keeps close along the line of the ribs. If the organ is neither unduly enlarged nor squeezed out of its place owing to the use of a tight corset, it does not project below the ribs, save where it crosses the space between the rib-cartilages below the end of the breast-bone. [Illustration]