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

Dangers due to the Absorp- tion of Nitrogen by the Blood. How to avoid the danger. to the existing pressure, but the tissues take up the gas at a much slower rate— a late which depends on the blood supply. Where this is good, as in the brain and spinal cord, the saturation is quick, but in the fibrous tissues about joints, etc., saturation is very slow. I hose tissues which are saturated quickly also give up theii sui plus nitrogen quickly, and those which saturate slowly also desaturate slowly. It is of the utmost service that the tissues of the diver take so long to get saturated with the air, as it much reduces the dangers due to short stays under water. The Greek divers will come up from 30 fathoms as fast as they can, but they make very short stays under water ; their time from surface to the bottom and return docs not exceed 10 minutes, so that their tissues are not sufficiently satu- rated to cause danger unless they make successive dives at short intervals of time. e must shortly refer to the various dangers which result from the for- mation of bubbles in the blood and tissues. In the first place they may come off in the blood vessels themselves, filling the right side of the heart with air, and causing death in a few minutes. In. less sudden cases the bubbles form in the brain or spinal cord, leading to paralysis of the legs (diver’s palsy), whilst in less serious cases we may only have severe pains in the joints and muscles. How are these dangers to be avoided? In the first place the diver must descend as quickly as he possibly can, i.e., as quickly as his ears and air supply will let him. Every minute spent in descending is time lost, since the body is becoming saturated with nitrogen all the time. A scale of time to be allowed on the bottom has been drawn up, during- which there is but little chance of the diver getting dangerously saturated. If the tissues are at all allowed to get fully satu- rated, the time required for safe desaturation is so great that it becomes very tedious loi the diver to hang" on to the shot rope. 1 here is absolutely no danger in a quick descent, provided that the ears are well open, and that the air pumps can keep the pressure in the dress-æqua! to that of the depth that the diver may be at. Of course, if the air pressure falls below that of the water, a quick descent would mean all the dangers of a fall, but this is not likely to happen, as the diver would Aciv quickly feel the “ nip ” of the too short supply of air, and instinctively hold on to the ropes until the supply has caught him up again. J sta-' al t’10 bottom must be governed by the table appended when the c ept is 9 fathoms 01 over. I his table has been drawn so as to leave little chance of the tissues getting saturated. In ascending, the diver is decompressing himself, and it is this gradual de- compression that is the most important factor in the prevention of accidents from the formation of bubbles of nitrogen. I he blood, we saw, could hold in solution about twice as much of the gas at any pressure as it would do if it behaved like water; we can therefore come up from 33 feet to the surface without fear of ill- effects. This relative amount of 2—1 of absolute pressures holds good up to high pressures, so that the diver at 7 atmospheres (198 feet or 33 fathoms) can come quickly up to 3J atmospheres (82 feet or about 14 fathoms),'or when at 6 atmo- spheres (165 feet or 27I fathoms) to 3 atmospheres (66 feet or 11 fathoms) with- out danger of bubbles forming. It will be seen how very important this law is, for the diver can come up quickly from the dangerous depths to a depth within r7