130 SECTIONAL ADDRESSES. 



in one special case, that of working in liigli pressurs air, whicli has involved 

 serious injury in the past to the men employed in very important work. 

 In this case, while death and injury occurred in a very high percentage 

 only a few years ago, the dangers have now been much reduced, thanks 

 to the civil engineer. Air under pressure is required in the sinking of 

 bridge foundation cylinders and in the driving of subaqueous tunnels, 

 and the resulting illness is commonly called caisson disease, diver's palsy 

 or ' bends,' the latter name being due to the bodily distortions of the 

 sufferers. This in its essence is a mechanical disease, and for this reason 

 the medical profession did not advance far in ascertaining its cause. It 

 was the civil engineer who through bitter experience and long-continued 

 observation, found a cure. Chance gave me, forty-eight years ago, while 

 at the Forth Bridge, the opportunity to study this disease during the 

 sinking of the caissons which were being built and sunk under air pressure. 

 At a later date the appalling death rate under the much higher pressures 

 and much worse conditions that attended the construction of the Hudson 

 Tunnel, New York, necessitated something being done to amehorate the 

 life of those who worked for me, and to make it possible to get the men 

 to face the dangers of carrying on the construction of this, the first 

 subaqueous tunnel built in the United States. The work had been 

 commenced many years before, and much pain and many deaths had 

 occurred, but without any cure having been discovered. Many months 

 of continuous observation on these undertakings enabled me to ascertain 

 certain facts and to devise a scheme of treatment — ^the use of recompres- 

 sion in a medical airlock — which is now always adopted on undertakings 

 where compressed air is being employed, and with great success. These 

 experiences also led me to discover contributory causes not realised up 

 to that time, namely, among others, the necessity for much purer air 

 than is required in workings at atmospheric pressure, and further the 

 benefits arising from stage decompression. I had mules continuously 

 under air pressure for many months, and they did not suffer at all from 

 this long immersion but, like human beings, they suffered badly on passing 

 through the air locks when coming out and getting back to normal atmo- 

 spheric pressure. By simple re-immersion in high air pressure and by 

 very slow decompression treatment, which is a very gradual withdrawal 

 of the pressure while still keeping the air pure, I was able to reduce the 

 death rate among the men at the Hudson Tunnel in 1890-2 from 25 per 

 cent, per annum to 1|. In the Blackwall Tunnel in 1893 there were no 

 deaths at all during the whole course of the works. Since those days 

 Prof. Haldane, Prof. Sir Leonard Hill and Captain Damant, to mention 

 the chief workers in this field, have carried the work of regulated decom- 

 pression further and brought the rough discoveries I made and introduced 

 to a more exact scientific basis ; and much greater depths of immersion 

 involving higher air pressures are now possible and safe by means of stage 

 decompression. Here is a case where the civil engineer has helped the 

 science of medicine — a return for some of the benefits received from the 

 bacteriologist and medical man. 



During my investigations I tried to ascertain the actual blood pressures 

 in the human body but so far these have never been taken. Only com- 

 parative, not actual, pressures can be taken, but I feel sure there is a great 



