continued in decreasing degree, without this being shown in the final result. The problem of the existence of a reserve supply of oxygen is in no way solved by these experiments. [69] _Rosenthal_: “Untersuchungen über den respiratorischen Stoffwechsel.” Arch. f. Anat. u. Physiologie physiolog. Abt. 1902 und Suppl. 1902. [70] _Falloise_: “Influence de la réspiration d’une atmosphère suroxygéné sur l’absorption d’oxygène.” Traveaux du laborat. de physiol. de L. Fredéric Liège, T. VI. [71] _Durig_: “Ueber Aufnahme und Verbrauch von Sauerstoff bei Aenderung seines Partialdruckes in der Alveolarluft.” Arch. f. Anat. u. Physiol. physiol. Abt. 1903 Suppl. [72] _Winterstein_: “Ueber den Mechanismus der Gewebeatmung.” Zeitschr. f. allgem. Physiol. Bd. VI, 1907. [73] _Lesser_: “Die Wärmeabgabe der Frösche in Luft and sauerstofffreien Medien. Ein experimenteller Beweis dass die CO_{2} Production der Frösche im sauerstofffreien Raum nicht auf Kosten gespeicherten Sauerstoffs geschieht.” Zeitschr. f. Biologie Bd. 51, 1908. In assuming the presence of a reserve supply of oxygen in the cell we must above all entertain no false conception as to its amount. This must be, as I have often had occasion to emphasize, exceedingly small and in no way comparable with the great masses of organic reserve substances contained in the cell. The assumption, especially for the _nerve centers_ of the frog, that the excitability remains after complete exclusion of oxygen must be looked upon as demonstrating a reserve supply of oxygen, would oblige one to suppose the presence of such a small store of oxygen that it would be completely exhausted by continued activity in room temperature within ten to twenty-five minutes. Strychninized frogs, in which the blood has been replaced by an oxygen-free saline solution, lose, as I have shown,[74] their excitability completely within ten to twenty-five minutes after the blood has been displaced. Nevertheless the assumption of the existence of a small oxygen supply in the cell can hardly be evaded. It must not be imagined that the moment the blood of the frog has been replaced with an oxygen-free solution, there is not a trace of oxygen left in the organism. Were such the case, the irritability, if measured by the extent of the response, would sink _momentarily_ to a very low level, for the anoxydative disintegration processes are associated with an incomparably smaller production of energy than those of oxydative disintegration. We see, however, that the irritability in the muscles, nerves and nerve centers of the frog even after the complete withdrawal of oxygen at first remains practically at the former height and only very gradually decreases. Above all it would seem to me to be in the interest of the preservation of the organism and especially of those parts in which there is a high energy production and particularly those substances in which energy production predominates, that the material