puscles of the frog by passing induction-shocks; and I find that the rate of formation of this compound through intracellular oxidation can be greatly accelerated by this means, especially in leucocytes, where the oxidation-rate is relatively rapid. I am inclined, therefore, to attribute to the variations in the electrical polarization of the membranes an important general role in varying the rate and possibly the character of the energy-yielding intracellular oxidations. On this view, intracellular metabolism would be largely controlled by membrane-processes. How this is possible may be illustrated by the case of anesthesia just discussed. The ether-impregnated plasma-membrane is relatively unaffected, as compared with the normal membrane, by isotonic sodium chloride solution; and consequently the stimulation, with its resultant increase in oxidation, is prevented by thus altering the membrane. The precise nature of the conditions in these and similar phenomena can be elucidated only by further study.
I had hoped to discuss the rôle of membrane-processes in other cellactivities, such as fertilization, cell-division and development, but the space at my disposal is insufficient. Before closing, however, I wish to refer briefly to the large class of physiological processes in which a regular rhythmical repetition of the same change, e. g., contraction, is the essential characteristic. Such processes include ciliary activity, the action of contractile vacuoles, the action of the heart and of nerve-cells like those of the respiratory center or the heart-ganglia of certain animals. In the division of cells during early development, a definite though slower rhythm is also seen. Now an electrical rhythm accompanies the physiological rhythm in muscle and nerve cells, probably in cilia, and almost certainly in dividing cells, as indicated by the experiments of Miss Hyde on dividing fish-eggs. The existence of a chemical rhythm—of carbon dioxide production—has been demonstrated in dividing cells (sea-urchin eggs) by Dr. Lyon, and we may infer its presence in the other rhythmical processes. The electrical rhythm indicates a rhythm of changing permeability, and of this there is some direct evidence in dividing egg cells. In all of these cases we have to do with automatic processes whose rhythm proceeds of its own accord, provided the external conditions remain normal. Each cycle in the rhythm furnishes itself the conditions for its own recurrence. The question arises: from what physico-chemical point of view is it best to regard this class of phenomena? In the case of a rhythmical contractile tissue three interdependent and synchronous rhythms may be distinguished—a chemical, a mechanical (presumably the expression of surface-tension changes), and an electrical. An elementary model of these phenomena is, I believe, furnished by the experiments of Bredig and his pupils on the rhythmical catalytic decomposition of hydrogen peroxide in contact with metallic mercury. When a ten per cent, solu-
