634 EVENING DISCOUKSES. 



EVENING DISCOURSES. 



FRIDAY, SEPTEMBER 1. 



The Physiology of Submarine Work. By Leonard Hill, M.B., F.R.S. 



Compressed air is used in all the great subaqueous works of to-day, in tun- 

 nelling, harbour works, shaft sinking in wet soil, pier and bridge building, 

 diving for pearl and sponges, salvage work, &c. The intercommunication of the 

 great cities of the world depends on tunnels built with the aid of compressed 

 air. All such works are limited to a certain depth by the pathological effects 

 produced on the workers. 



The Naked Direr. 

 . The naked diver preceded the diver who uses compressed air. The body of 

 the naked diver is pressed upon by the water, equally and in all its parts, by 

 a pressure equal to one atmosphere (15 lb. per square inch) for every 33 feet 

 (10'3 m.) of depth. He takes a deep breath or two, fills his lungs before, and 

 holds his breath during the dive. He places a foot in a stirrup attached to a 

 heavy stone, and so is carried rapidly to the bottom. The air in his lungs, air 

 passages, and middle ear must be compressed to half its volume at 33 feet 

 (2 atmospheres absolute), to one-third at 66 feet (3 atmospheres absolute), to a 

 quarter at 99 feet (4 atmospheres absolute). The depths attained are usually 

 not greater than 60 to 70 feet. The compression of the air in the lungs is 

 rendered possible by the upward movement of the diaphragm and sinking' in 

 of the abdomen. Some of the air in the lungs must dissolve in the blood accord- 

 ing to the law of partial pressures. 



The amount of nitrogen dissolved from air at 1 atmosphere pressure and at 

 body temperature is 085 per cent. This is the figure for the watery part of the 

 body. The fat dissolves about 5 per cent., an important fact discovered by 

 Vernon. At 66 feet (3 atmospheres) the watery part can hold 085 x 3 and 

 the fat 5x3 per cent. Putting the fat against the solids of the body 

 (bones, &c), which do not dissolve gas, it may be assumed that the whole body 

 dissolves about 1 per cent, of nitrogen per atmosphere. A man weighing 

 60 kgm., then, will dissolve when compressed from 1 to 3 atmospheres about 

 1,200 c.c. of nitrogen, 'that is, if time were allowed for the blood to convey the 

 nitrogen from the lungs to the tissues till saturation occurred. In the lungs 

 there are about 4,000 c.c. of air. Of course, far loss than 1,200 c.c. will be 

 dissolved in the minute the diver is submerged. In addition to the solution 

 of nitrogen, the blood will take up more oxygen, both in solution and chemically 

 combined with the hemoglobin ; the diver working hard gathering pearl or 

 sponge will use oxygen rapidly. It is clear, then, that the absolute volume of 

 air must be reduced during the minute the diver stays submerged, but it is 

 difficult to estimate by how much. To allow for the reduction of volume, both 

 by compression and solution, in the body, it is clear that the diver must fill his 

 lungs well, otherwise the diaphragm will be pushed up to such an extent that 

 the action of his heart and the circulation of the blood become impeded. It is 

 this, in part, which sets a limit to the depth to which the naked diver can go. 

 The bleedings, from mouth and nose, which the unpractised naked diver suffers, 

 are due. no doubt, to both the congestion of the blood which results from holding 

 the breath and to rarefaction of the air in the nose and middle ear during the 

 ascent. Some time ago I put this question to Sir E. Eay Lankester : What 

 happens in the case of the whale which sounds, perhaps, to a depth of 1,000 feet ? 

 Does the whale allow the lungs to fill with water as the air becomes compressed 

 to one-thirtieth of its volume; if not, what is the mechanism engaged which per- 

 mits such compression ? I fancy the whale allows water to enter, and blows this 

 out again when it ascends to the surface. The naked diver can extend his stay 

 under water by deep breathing before the plunge and filling the lungs with 



