1906.] on Compressed Air and its Physiological Effects. 365 



of the blood in the deeper parts of the l)ody can be induced by 

 variations of atmospheric pressure, is contrary to physical principles, 

 and is quite untenable. 



I can refute it by the following experiment : A frog's web is 

 stretched over the glass window of a pressure chamber, and is 

 illuminated by the arc light, so that the circulation of the blood is 

 projected on the screen. The circulation remains unchanged when 

 the pressure is raised to 20 atm. Manometric records of blood 

 pressure in mammals also show no noteworthy change. 



That mere mechanical pressure uniformly applied is of little im- 

 portance to living matter is shown by the existence of life in the 

 greatest depths yet sounded, where the superincumbent pressure may 

 equal 2 to 8 and even 5 miles of water. 



The use of compressed air for submarine work was a matter of 

 slow development, owing, not to lack of invention, but to want of 

 efficient air pumps and flexible tubes. The oldest invention is that 

 of a pipe conveying air from the surface to the mouth of the diver. 

 Such a device cannot be used at any depth, because the body is 

 pressed upon by the water plus the atmospheric pressure, while the 

 lungs are exposed to the atmospheric pressure alone. The pressure of 

 the water on the body makes breathing difficult and congests the blood 

 within the lungs. The cupping glass demonstrates the congestive 

 effect produced by lessening the atmospheric pressure at one part of 

 the body only. 



The same bad conditions pertain to the w^ater-tight metal helmet, 

 combined with leather dress, suggested by Borellus (17th cent.), the 

 diver being supposed to live on the air in the helmet. 



Bernouilli formulated the correct theory that the diver must 

 either be supplied with air at the pressure of the water surrounding 

 him, or that Borellus' helmet must be made of leather so that the air 

 within can be compressed by the water. The Venetians (17th cent.) 

 pumped air into a diver's helmet with a bellows, and thus forestalled 

 by two centuries the modern diving dress of Siebe, Gorman and Co. 



Any one 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 33 J ft. the air in such a bell is 

 compressed to half its volume, and this, together with lack of ventila- 

 tion, 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 dis- 

 placed the air into the bell. He descended co 1) to 10 fathoms with 

 four others, and used up 7 to 8 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 



