flacidity with a drop in breathing rate and transition to convulsive breathing with 3 to 4 breaths per minute until complete cessation of breathing of 45 seconds duration (post-hypoxemic pseudo-death—Lutz). Then follows a period of improvement in breathing, until the first subconsciousness movements announce the gradual recovery of consciousness, during which, nevertheless, the higher mental functions are temporarily entirely absent. Further recovery proceeds slowly during the course of the following ½ to 1½ hours as may be seen from the above case record. During the time of complete unconsciousness, there was defecation and urination in the case of most subjects, increased salivation and, in some cases, vomiting. Here we obviously have the conditions which Lutz and Wendt in their animal experimentation which is referred to in greater detail later found in falling experimentation with O_{2} breathing and designated as “post-hypoxemic twilight state” (“Posthypoxaemischen Daemmerzustand”) since we are dealing with a slow recovery of consciousness, especially also in view of the mental behavior of the experimental subjects. The post hypoxemic pseudo-death observed by Wendt and Lutz was not found in any experiments in the form which they had observed. The severe condition described above we could designate as hypoxemic pseudo-death only because it was limited to the period of the most severe O_{2} lack (on the average, between 13.3 and 12.3 km.). In spite of the relatively large number of experiments, the actual cause of the severe mental disturbances and bodily failures (paralysis, blindness, etc.) attendant upon post-hypoxemic twilight state remains something of a riddle. It appeared often as though the phenomena of pressure drop sickness had combined with the results of severe oxygen lack. In this connection, the subjective accounts made by the authors in two experiments each were interesting. In the case of Ro. during a half hour stay at 12 km. [39,400 ft.] with oxygen, [page 17 of original]