cooling, but is only brought about when at the same time a renewed oxygen supply is provided. For instance, a frog is depressed in the warm chamber and even when a strychnine injection has been introduced, does not show the slightest reaction to stimuli. In the warm water bath artificial circulation is now applied in the previously described manner with an oxygen-free saline solution at 30° C., so that the blood is displaced and thus the renewed oxygen supply to the nervous centers prevented. The animal can now be cooled and the warm saline solution be replaced by a cooled one without the least recovery taking place. If, however, blood of the ox with contained oxygen is substituted for the oxygen-free saline solution, the frog shows signs of recovery within a few minutes and after ten or fifteen minutes responds as a result of the strychnine to the merest touch with tetanic contractions of the whole body. By modifying these methods of investigation to a certain extent _Bondy_[203] has confirmed these results to the fullest extent. Later _Winterstein_ by quantitative determinations of oxygen consumption on medusæ showed that at 30–35° C., at which temperature heat depression sets in, the consumption of oxygen shows an increase of about three and a half times compared to that in a temperature of 11–12° C. These facts show that we have in heat depression a process which, as far as its genesis is concerned, is completely analogous to that of fatigue. In fatigue, a relative want of oxygen is produced by the increased consumption following functional activity, in heat depression by the increase of the entire metabolism producing a corresponding increase of oxygen requirement. In both instances we have an excitation produced by external stimuli which result in an increase in the amount of oxygen required, and in both instances the oxygen at disposal is not sufficient to permanently meet the augmented demand. In both types, therefore, decomposition must become more and more anoxydative and the well-known series of processes is developed, which find their expression in depression. [202] _H. Winterstein_: “Ueber die Wirkung der Wärme auf den Biotonus der Nervenzentren.” Zeitschr. f. allgem. Physiol. Bd. I, 1902. The same: “Wärmelähmung und Narkose.” _Ibid._ [203] _Oskar Bondy_: “Untersuchungen über die Sauerstoffaufspeicherung in den Nervenzentren.” Zeitschr. f. allgem. Physiol. Bd. II, 1904.