tion of the lungs. The very same thing happens when we take gentle exercise and produce more in our bodies.
At each breath we rebreathe into our lungs the air in the nose and large air-tubes (the dead-space air), and about one third of the air which is breathed in by a man at rest in dead-space air. Thus, no man breathes in pure outside air into his lungs. When a child goes to sleep with its head partly buried under the bed-clothes, and in a cradle confined by curtains, he rebreathes the expired air to a still greater extent, and so with all animals that snuggle together for warmth's sake. Not only the new-born babe sleeping against its mother's breast, but pigs in a sty, young rabbits, rats and mice clustered together in their nests, young chicks under the brooding hen, all alike breathe a far higher percentage than that allowed by the Factory Acts. To rebreathe one's own breath is a natural and inevitable performance, and to breathe some of the air exhaled by another is the common lot of men who, like animals, have to crowd together and husband their heat in fighting the inclemency of the weather.
In the Albion Brewery we analyzed on three different days the air of the room where the generated in the vats is compressed and bottled as liquid carbonic acid. "We found from 0.14 to 0.93 per cent. of in the atmosphere of that room. The men who were filling the cylinders and turning the taps on and off to allow escape of air must often breathe more than this. The men engaged in this occupation worked twelve-hour shifts, having their meals in the room. Some had followed the same employment for eighteen years, and without detriment to their health. It is only when the higher concentrations of are breathed, such as 3 to 4 per cent, of an atmosphere, that the respiration is increased, so that it is noticeable to the resting individual; but percentages over 1 per cent, diminish the power to do muscular work, for the excess of produced by the work adds its effect to that of the excess in the air, and the difficulty of coordinating the breathing to the work in hand is increased.
Haldane and Priestley found that with a pressure of 2 per cent, of an atmosphere of in the inspired air the pulmonary ventilation of a man at rest was increased 50 per cent., with 3 per cent, about 100 per cent., with 4 per cent, about 200 per cent., with 5 per cent, about 300 per cent, and with 6 per cent, about 500 per cent. With the last, panting is severe, while with 3 per cent, it is unnoticed until muscular work is done, when the panting is increased 100 per cent, more than usual. With more than 6 per cent, the distress is very great, and headache, flushing and sweating occur.
Divers who work in diving dress and men who work in compressed air caissons constantly do heavy and continuous labor in concentrations of higher than 1 per cent, of an atmosphere, and so long as the
