632 TRANSACTIONS OF SECTION I. 
the mines could be safely worked and illuminated with electricity, and miners’ 
nystagmus prevented, for this is due to the dim light of the safety lamp. The 
problem possibly may be solved by purifying and cooling the return air, and 
mixing and circulating this with a sufficiency of fresh air. 
Owing to the fact that the percentage of CO, is the usual test of ventilation 
and that only a very few parts per 10,000 in excess of fresh air are permitted by 
the English Factory Acts, it is generally supposed that CO, is a poison and that 
any considerable excess has a deleterious effect on the human body. No sup- 
position could be further from the truth. 
The percentage of CO, in the worst ventilated room does not rise above 
0:5 per cent., or at the outside 1 per cent. It is impossible that any excess 
of CO, should enter into our bodies when we breathe such air, for whatever the 
percentage of CO, in the atmosphere may be, that in the pulmonary air is kept 
constant at about 5 to 6 per cent. of an atmosphere—by the action of the 
respiratory centre. Jt is the concentration of CO, which rules the respiratory 
centre, and to such purpose as to keep the concentration both in the lungs and in 
the blood uniform (Haldane); the only result from breathing air containing 
0°5 to 1 per cent. of CO, is an inappreciable increase in the ventilation of the 
lungs. The very same thing happens when we take gentle exercise and produce 
more CO, 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 analysed on three different days the air of the 
room where the CO, generated in the vats is compressed and bottled as liquid 
carbonic acid. We found from 0°14 to 0°93 per cent. of CO, 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 with- 
out detriment to their health. It is only when the higher concentrations of CO, 
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 CO, pro- 
duced by the work adds its effect to that of the excess in the air, and the 
difficulty of co-ordinating 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 CO, in the inspired air the pulmonary ventilation of a man at rest 
was increased 50 per cent., with 3 per cent. about 1U0 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 labour in concentrations of CO, higher than 
1 per cent. of an atmosphere, and so long as the CO, is kept below 2 to 3 per 
cent. they are capable of carrying out efficient work. In the case of workers in 
compressed air it is important to bear in mind that the effect of the CO, on the 
breathing depends on the partial pressure and not on the percentage of this gas in 
the air breathed, : 
