This result is of great importance. Burdon Sanderson, the late learned professor of physiology at the University of Oxford, has not hesitated to compare it to the discovery of respiratory combustion by Lavoisier. There is no doubt some exaggeration in the comparison; but there is, on the other hand, no less exaggeration in supposing that it is not of great importance. We may no longer in these days speak without reservation of the vital vortex of Cuvier, and of the incessant twofold movement of assimilation and dissimilation which is ever destroying living matter and building it up again. In reality, the living protoplasm varies very little; it only undergoes oscillations of very slight extent; it is the materials, the reserve stuff on which it operates, which are subject to continual transformations. _Chemical Composition of Protoplasm._—One of the the three characters attributed by Ch. Robin to living matter was its chemical composition, of which little was known in his time. He insisted on the constant presence in the living elements of three orders of immediate principles—proteid substances, carbohydrates, and fatty bodies. In reality the proteid substances, or albuminoids, alone are characteristic. The two other groups, carbohydrates and fatty bodies, are rather the signs and the products of the vital activity, than constituents of the matter on which it is exercised. It is therefore on the knowledge of the proteid substances that all the sagacity of biological chemists has been exercised. Their efforts for thirty years, and particularly in the last few years, have not been barren; they enable us to give a first rough sketch of the constitution of these substances. § 1. THE CHARACTERISTIC SUBSTANCES OF THE PROTOPLASM. THE NUCLEO-PROTEIDS.