364 Mr. Leonard Hill [May 25, 



WEEKLY EVENING MEETING, 



Friday, May 25, 11)06. 



His Grace the Duke of Northumberland, K.G. P.O. 

 D.C.L. F.R.S., President, in the Chair. 



Leonard Hill, Esq., M.B. F.R.S. 



Compressed Air and its Pliysiological Effects. 



Co^ipressed air is used in all the great subaqueous works of to-day^ 

 in tunnelling-, pier sinking, bridge building, diving, etc. All such 

 works are limited to a certain depth by the pathological effects pro- 

 duced on the workers. 



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 -f 1 atm. (15 lb. per 

 sq. in.) for every ;->P>^ ft. (10 'o m.) of depth. He fills his lungs 

 before, and holds his breath during, the dive. The air in his lungs 

 must l)e compressed to half its volume at :'>o| ft. (2 atm. al)s.), to 

 one-third at 67 ft. {?■> atm. abs.), to a quarter at lOOj ft. (-l atm. abs.), 

 and so on.* The depths attained are usually not greater than 

 60-70 ft. 



The duration of his stay under water is limited by the oxygen- 

 carrying power of his l)lood. This may become greater by practice. 

 Diving birds have double tlie normal volume of blood (Bohr). The 

 diver who uses gear, or the caisson worker, is surrounded with com- 

 pressed air and ])reathes freely in it. The body of either is pressed 

 upon by the air, and the air pressure must always be just greater than 

 that of the water to keep the latter out of the helmet, bell, or caisson. 

 Whether it ])e air or water that uniformly presses upon the body the 

 tissue fluids transmit the pressure equally throughout the body, and 

 thus although it is computed that -|- 1 atm. means an additional total 

 pressure of 15,000 to 20,U0(I kilograms (40,000 lb.) on the body of a 

 man, no mechanical effect is produced. Living matter is a colloidal 

 solution, containing about so per cent, of water, and is practically 

 incompressible. 



The theory, put forward ])y many medical writers, that congestion 



* The squid eating whale, according to the Prince of Monaco, finds its 

 feeding grounds at depths of 4000 ft. Is the volume of air in its lungs com- 

 pressed to the lOOth part ? 



