The experiments herein described were carried out at the works of Messrs. Siebe Gorman, Ltd., with the co-operation of Sir Robert Davis, who kindly placed at the author's use the necessary apparatus. A small cylindrical copper chamber was used about 20 inches long and 12 inches wide. One end was hermetically closed, and the other fitted with a removable lid; a thick glass disc formed the larger part of this lid, and served as an observation window. An air-tight junction was made between the lid and the chamber by means of thick rubber washers lubricated with glycerine. When a positive pressure was used a set of bolts and nuts secured the lid to the chamber and made the closure air-tight. The chamber was made to withstand pressure up to +130 lbs. It was fitted with valved inlet and outlet tubes; one tube connected the chamber with a pressure gauge. For evacuating the chamber and studying the effect of low pressures, an efficient pump was used with the piston working in oil. The stroke of the pump was driven by a band off the workshop shafting. The chamber was evacuated by this means down to the lowest pressure required (70 mm Hg), in about 6 minutes. To indicate the pressure during evacuation the chamber was connected to the top of a barometer tube, which was fitted with a scale; the bottom of this tube dipped in a cup of mercury. The chamber was placed in the vertical portion, and a wooden platform arranged inside on which the animals rested in full view under the glass window. The opening of the inlet tube used for ventilating the chamber was carried below this platform, so that the chamber could be thoroughly washed out with oxygen, or a mixture of oxygen and nitrogen. After the animals,
e. g
., two rats, had been introduced, and the chamber closed, the inlet tube was connected, in the first series of experiments, with a cylinder of oxygen (99%) and the chamber well washed out with this gas. It was then repeatedly evacuated down to about 150 mm Hg, oxygen being admitted each time. This procedure secured a purity of oxygen in the chamber, as was shown by analysis. Finally the chamber was evacuated down to the pressure whereat symptoms of acute dyspnœa became manifest, a slow inflow of oxygen being maintained during this evacuation. The animals settle down, and quietly rest on the platform during the final evacuation, that is until the pressure drops to about 100 mm Hg, they then become restless, and when the pressure drops to 90-80 mm Hg their breathing becomes very deep and slow and they slow other signs of want of oxygen. Rats make convulsive leaps towards the window of the chamber, and on coming to rest their limbs straddle out, guinea pigs and pigeons fall over, monkeys close their eyes and fall asleep when the pressure falls below 120-110 mm Hg, and then as the pressure falls below 100 sink lower and lower down, but are still able to balance themselves in the sitting posture. Below 90 mm Hg the head falls against the side of the chamber and the monkey is unable to recover its balance when the chamber is shaken. The animals quickly recover when oxygen is let in, thus the evacuation could be repeated several times with like result, bloats were observed in a larger chamber which took about 35 minutes to evacuate. They were at first in the standing posture, but lay down when the pressure fell to 100-90 mm Hg and made convulsive movements when it reached 90-80 mm Hg.
Wooden platform as a hand table