Oxygen equipment is absolutely necessary at these altitudes, since it assures the most favorable conditions for the jump. In case of failure of the equipment, loss of the mouthpiece or other mishaps, we still need not count upon serious disturbances or injuries up to 20 km. [65,600 ft.]. Even jumps from 21 km. [68,900 ft.] will go well if there is automatic opening of the parachute through barometrical control at 7 to 4 km. [23,000 to 13,100 ft.] altitude. The automatic opening is also essential for several other reasons: 1. In particular cases the parachute jumper is not able to regain consciousness at a sufficient altitude above the ground because of collapse or injury. 2. As a result of cold the jumper may be handicapped by immobility of his hands, and thus be hindered in pulling the rip cord. 3. As a result of the unconsciousness resulting from anoxia, the [page 27 of original] parachute jumper loses all sense of the time which has elapsed since his jump, as was shown in all experiments, so that it is impossible for him, with failing eyesight, to estimate his altitude. On the other hand it is desirable, on the basis of the reason adduced under number 3 above, that the opening of the parachute at altitudes above 7 km. [23,000 ft.] be prevented, since very often the parachute jumper would pull the rip cord immediately after recovering from his altitude sickness, which may be too soon and at too high an altitude. The best conditions for explosive decompression itself and for the seconds elapsing until the appearance of altitude sickness are provided if flying is done at a cabin pressure corresponding to 8 km. [26,300 ft.] and with oxygen breathing. Since it may become necessary to abandon the aircraft for reasons other than damage to the pressure cabin, the pressure equalization at a predetermined rate must be made possible by means of a valve. In case abandonment does not appear necessary in spite of the loss of cabin pressure the danger of oxygen lack is still less with the automatic diving control mechanism than in a parachute jump, since the dive may be made with considerably greater rate of descent. VI. Summary Experiments were instituted upon the possibility of rescue from altitudes up to 21 km. [68,900 ft.]. Without parachute oxygen equipment, rescue in descending experiments is still possible from 13 km. [42,700 ft.], with equipment, from 18 km. [59,100 ft.]. The danger arising from cold must be considered. In falling experiments, rescue from 21 km. [68,900 ft.] altitude with and without oxygen was proved possible. Automatic parachute opening is necessary. Ebullition of the blood does not yet occur at 21 km. [68,900 ft.] altitude. [page 28 of original]