permanent nonirritability, that is, into complete fatigue. [152] _Hermann_: “Untersuchungen über den Stoffwechsel der Muskeln ausgehend vom Gaswechsel derselben.” Berlin 1867. [153] _Joteyko_: “La fatigue et la respiration élémentaire du muscle.” Paris 1896. [154] _Julius Vészi_: “Zur Frage des Alles oder Nichts Gesetzes beim Strychninfrosch.” Zeitschr. fur allgem. Physiologie Bd. XII, 1911. [Illustration: Fig. 35. Double glass chamber for comparative experiments on fatigue of the nerve (_n n_). A and B--Wires of the electrodes. (After _Thörner_.) ] [Illustration: Fig. 36. Curve of action current of two nerves, one of which is stimulated (plain line) whilst the other remains at rest (dotted line). After decrease of irritability of the stimulated nerve in nitrogen, oxygen is introduced into the chamber and irritability increases again. Then the previously resting nerve is stimulated in nitrogen and the stimulated nerve remains at rest. (After _Thörner_.) ] The knowledge that fatigue represents a prolonged refractory period resulting from relative deficiency of oxygen has enabled me with the aid of my coworkers to demonstrate the existence of fatigue and produce the typical symptoms experimentally for a living tissue, which up to then was considered indefatigable: I refer to the medullated nerve. After having found that the condition necessary for the production of fatigue in the nervous centers is a deficiency of oxygen, I arrived at the conclusion that fatigue could only be obtained in the medullated nerve when subjected to a deficiency of oxygen. Up to that time, however, no consumption of oxygen was known for the nerve. It was, therefore, necessary to first ascertain if the nerve possessed an oxydative metabolism. At my request, _H. von Baeyer_ investigated these questions. After many vain attempts to obtain absolutely pure nitrogen, we finally succeeded in finding a method by which it is possible to gain nitrogen gas, which is, one might almost say, in a mathematical sense absolutely pure. It was then possible for _H. von Baeyer_[155] to asphyxiate the nerve and subsequently to bring about complete restoration by the introduction of oxygen. It was shown that the nerve requires merely a minute quantity of oxygen and only completely asphyxiates when the last trace of oxygen is removed, and further that recovery takes place within a fraction of a minute if the oxygen is again supplied. These experiments which have been carried further by _Fröhlich_[156] were afterwards confirmed in other laboratories,[157] and _form_ the basis for proving the existence of fatigue of the medullated nerve. Shortly after, _Fröhlich_[158] was able to demonstrate symptoms of fatigue in the medullated nerve. He found that the refractory period of the nerve, which, as previously mentioned, _Gotch_ and _Burch_ fixed at about .005 second duration, was prolonged by oxygen deficiency to .1 second, so that stimuli