5 68 



NATURE 



[October 26, 191 1 



I have noted that the same false views are even now 

 put forward in the daily Press to explain the symptoms, 

 due to the rarefaction of the air, endured by aeroplanists. 

 The sickness of high altitudes suffered by mountain 

 climbers, balloonists, and aeroplanists has nothing to do 

 with the mere mechanical effect of the lowering of baro- 

 metric pressure. In an atmosphere enriched with oxygen 

 U. Mosso has endured a lowering of barometric pressure 

 until he could span the height of the column of mercury 

 in the barometer with his hand. Oxygen want, due to the 

 rarefaction of the air, is the prime cause of altitude sick- 

 ness. At an altitude of 18,000 feet, where the barometric 

 pressure is halved, a man, filling his lungs with air, takes 

 in only half the weight of oxygen which he takes in at 

 sea-level. His respiratory and circulatory organs can 

 scarcely work hard enough for the body to get enough 

 oxygen. The extra pulmonary ventilation washes the CO, 

 out of the body, and produces a subnormal concentration 

 of CO, in the blood and tissues. This is partly the cause 

 of mountain-sickness. Individual variations in immunity 

 to this sickness probably depend on variations in the 

 chemical quality of the blood and power of the hajmoglobin 

 to combine with oxygen. 



That mere mechanical pressure, uniformly applied, is of 

 no importance to living matter is shown by the existence 

 of life in the greatest depths yet sounded, where the super- 

 incumbent pressure may equal two, three, and even five 

 miles of water. By means of a small chamber and 

 hydraulic pump and lantern I can project the shadow of the 

 frog's heart beating in a suitable salt solution at a pressure 

 of 2000 lb. (133 atmospheres), equivalent to a depth of 

 nearly a mile of water. Regnard has compressed living 

 aquatic animals, frogs' muscles, &c, to 500 and even 1000 

 atmospheres, and has found at the highest pressures the 

 tissues become stiff and take up water, and life is 

 destroyed. His experimental results and those of the deep- 

 sea soundings (Challenger reports) are in contradiction. 

 Regnard's experiments require repetition, with careful 

 attention to the chemical composition of the water in which 

 the living matter is compressed. 



I refute the mechanical theories of compressed-air illness 

 by this experiment : a frog's web is stretched over the 

 glass window of the small pressure chamber, and is 

 illuminated by the arc light, so that the circulation of 

 the_ blood is projected on the screen. The circulation re- 

 mains unchanged when the pressure is rapidly raised to 

 twenty or even fifty atmospheres. 



Manomerric records of blood pressure taken from 

 mammals enclosed in a pressure chamber, or from man, 

 show no noteworthy change when the pressure is raised 

 to three atmospheres. Similarly, I now show that a frog's 

 heart or muscle contracts normally when suddenly sub- 

 mitted to_ a pressure of air equal to fifty atmospheres. 

 After a time the contraction languishes ; but that is not 

 due to the pressure per se, but to poisoning bv the high 

 pressure (concentration) of oxygen. The pressure uniformly 

 applied has no mechanical effect on the living protoplasm. 



The Evolution of Diving Apparatus. 

 The use of compressed air for submarine work was a 

 matter of slow development, owing, not to lack of inven- 

 tion, but to want of efficient air pumps and flexible tubes. 

 The naked divers had a barrel, or bell-shaped vessel, stand- 

 ing on a tripod, lowered down to them full of air, to 

 which they could return and breathe the air within every 

 minute or twi I [so chewed pieces of sponge dipped 



in oil. prok. -wallowing inhibits the respirs 



tory centre and checks the desire to breathe. One of the 

 oldest inventions is that of a pipe conveying air from the 

 surface in lb,, mouth of tlie diver. Such a device cannot 

 be used at any depth, because the bo.lv is pressed upon bj 

 the water plus the atmospheric pressure, while the lungs 

 exposed to the atmospheric pressure alone. ["his 



thing difficult, 11 .1 darigi rouslj ■ 1 I : the 



lungs with blood, as I can demonstrate by this 1 1.1 



[la also demonstrates the coin-' tive • lie. t 



produced by lessening thi atmospherii pn ui .1: part 



of the body only. Bernouilli (seventeenth centum formu- 

 lated the correct theorv that the diver must be supplied 

 with air at the press,,,,, ol the water surrounding him. 

 aped from under the 



NO. 2 191, VOL. 87] 



helmet, and only the head was dry. The air pressure in 

 the modern diving dress (invented by Siebe), regulated by 

 a valve in the helmet, keeps the water from entering at 

 the wrist cuff, and the whole body is kept dry and warm 

 and equally compressed. I demonstrate the modern diving 

 dress which Messrs. Siebe, Gorman and Co. have lent me 

 for this lecture. The pressure produced by the pump must 

 keep up to that of the water as the diver descends, so 

 long as he does not fall down. He can descend rapidlv, 

 e.g. 100 feet in two minutes ; but it is dangerous to fall 

 down, for if the pump does not keep up with the water 

 pressure a cupping effect is produced, and the diver may 

 suffer haemorrhage from the lungs and mouth and nose. 



By means of the escape valve the diver can adjust his 

 specific gravity so that he is only slightly heavier than 

 water, and can move easily along the bottom. He tills 

 his dress more or less with air, just as the fish fills its 

 swim bladder. If the dress becomes over-filled the diver 

 is " blown up " to the surface ; and in the old style of 

 dress he may become helpless, arms and legs blown out 

 stiff, unable to open his valve. You see how this happens 

 in the case of the model diver. To prevent this accident 

 the legs of the latest fashionable dress are laced up, as I 

 now show you. 



The Diving Bell and Caisson. 



Anyone who pushed an inverted glass under water and 

 saw it did not fill would conceive the idea of a diving bell. 

 Sinclair (1665) fashioned a simple wooden bell to recover 

 treasure from an Armada ship off Mull. At 33A feet the 

 air in such a bell is compressed to half its volume, and 

 this, together witli lack of ventilation, rendered such a bell 

 of little use. 



Halley, the astronomer, used a pipe and bellows for 

 shallow work, while for deep work, when his bellows 

 failed, he sank a cask full of air to a deeper level than 

 the bell. From the cask to the bell passed a tube, and 

 the water, entering the cask through a hole, displaced the 

 air into the bell (model demonstrated). He descended to 

 nine to ten fathoms with four others, and used up seven 

 to eight barrels of air. 



With the building of efficient air-pumps, Smeaton (1778) 

 applied the bell to the important use of building the piles 

 of bridges. Triger (1839) applied it to the sinking of coal 

 shafts through quicksands, and the bell became thus 

 evolved into the modern caisson — a steel chamber provided 

 with a cutting edge below and an air-lock above for allow- 

 ing the men to enter and leave without raising the bell. 

 Finally, the miss,,,, was applied to the purpose of hori- 

 zontally tunnelling under rivers. To effect this a steel 

 shield provided with cutting edge is driven forward by 

 hydraulic jacks. Screens are placed in the shield to allow 

 excavation of the soil in front of it. As fast as the shield 

 is driven forward, segments of the iron tunnel are built 

 into place. Water is kept out of the work by the use of 

 compressed air. On entering, the men are "com] 

 in the air-lock. i.e. the air pressure is raised to that in the 

 tunnel, and on leaving the tunnel they are " decompressed," 

 i.e. the air pressure is lowered in the loci; down to the 

 normal, so that the outer door of the lock may he op, ned. 



A diver is " compressed " on descending into the water, 

 as the pressure of his air-pump always keeps up to that 

 of the water. On coming up he is "decompressed." 



The Ventilation of the Diving Dress. 

 Divers in deep-sea water have in the past been unable 

 to stay down long owing to a feeling of oppression, which 

 they have ascribed to the pressure of the water. M. 

 Greenwood and I have exposed ourselves in our com- 

 pressed-air chamber to +02 lb. (seven atmospheres) and 

 + 7S lb. (six atmospheres) respectively, and found our 

 breathing just as free and easy as at atmospheric pressure. 

 Beyond the increasing nasal twang of the voice there are 

 1.0 symptoms produced, and there is no sense by which the 

 pressure can be estimated. John Haldane has dot 

 service in proving thai the cause of the oppression is due 

 ed partial pressure of CO, in the helmet owing 

 to deficient ventilation. The breathing is regulated by the 

 pressure of CO. in the lungs, so that this is kept at ; to 

 11 pet cent, of an atmosphere. During work the amount 



