Submarine Appliances And Their Uses
Deep Sea Diving, &c., &c.

THE PHYSIOLOGY OF DIVING. The produc- tion of Carbonic Acid Gas in the body. To produce energy we have (p use up ,fuel in one form or another. In the steam engine we burn coal, in an internal, combustion enp-ine petrol .oiicoal ças, and • , ”, t • AtAîWsl ( T k ’jUMpr©' Ai in the body certain constituents of the tissues. In each case oxygen is combined with the carbon of the fuel, and carbonic acid gas is formed, together with water vapour. Respiration is the process by which air is drawn into the lungs and, in turn, expelled. The blood in its passage through the lungs receives oxygen from the air, and gives up the carbonic acid gas and water. (Carbonic acid gas will be denoted in future by its formula CO2.) The greater part of this exchange takes place in the minute recesses/ of the lungs. The amount of CO2 given off by the lungs will depend on several factors, such as the amount of work that is being done, or the kind of food that has been eaten. If there is much CO2 to be given off we shall require much air to wash out the lungs, also if there is much CO2 in the air that we are breathing it is evident that we shall require a greater quantity of air to flush them out. This washing out of the lungs is best effected by increasing the depth of the respirations, and not by increasing their frequency. If, when a diver is in deep water, the rate of his respiration is counted, it will be found to be the same as when at the surface, provided the air supply is adequate. Dangers of Carbonic A cid Gas at the surface. The popular idea of the danger of CO2 in the air is much exaggerated. In fresh air there is only .03 per cent, of CO2, and if we are at ordinary atmospheric pressure, and provided we are at rest, it is not until we get this percentage in- creased a hundred times that we even begin to feel its effects in any way. Where this percentage (3 per cent.) is reached we find that we begin to breathe deeper than usual, and it has been found that this amount of CO2 causes us to breathe about twice as deeply as we usually do. At 6 per cent, there is severe panting-, at 10 per cent, there is extreme distress, and at a slightly higher percentage loss of consciousness occurs, which at 25 per cent, very gradually deepens into death. Effects of Carbonic Acid Gas at different pressures. Whilst the above is true for the effect of CO2 at the normal pressure, it has been found that it does not hold true when the air is under pressure. In this case, to estimate the effect of the CO2 the percentage present must be multiplied by the absolute pressure, when the effect on the human body will correspond with that produced by the new percentage at normal pressure. For instance, at 33 feet 1 per cent, of CO. has exactly the same effect as 2 per cent, has at the surface, or as 0.5 per cent, would have at 99 feet. In other words the deeper a diver descends the greater is the effect of a small percentage of CO2 in the helmet. Air supply required by Diver. It will be seen that the danger from the accumulation of CO2 in the dress is not an imminent one, and the pumps can usually be stopped for at least four minutes before the CO2 would accumulate to a serious extent, and, if the diver is ascending at the time, for much longer. How much air does a diver need? We saw that when CO2 reached 3 per cent, a man at rest at ordinary atmospheric pressure feels it. If he is working at the time 3 per cent, will cause him distinct discomfort. From a very large number of analyses of air issuing from the diver’s helmet, we have found that he produces about .014 cubic feet of CO2 (measured at atmospheric pressure) in one minute when at rest on the bottom at all depths, and about .045 cubic feet (measured at atmospheric pressure) when at work. From 15