252 EFFECT OF WATER PRESSURE ON BIOPLASM 



unsafe to expose a man for more than a very few minutes to 

 2 or 3 atm. 2 . 



Snell has laid particular stress on the importance of free 

 ventilation in caissons. He says that the sickness increases 

 whenever the C0 2 tension rises to 0-1 per cent. atm. C. Ham 

 and the writer have found that a tension of C0 2 of 3-4 per cent, 

 atm. produces dyspnoea equally when an animal is exposed to 

 compressed air or to ordinary air. Thus 1 per cent, of C0 2 in 

 the air breathed at 4 atm. pressure has the same effect as 

 4 per cent, at 1 atm. Such high tensions of C0 2 as 1-4 per cent, 

 seemed to have no particular influence on the dangers of decom- 

 pression. Any agent which produces exhaustion of the work, 

 such as hot moist air, CO arising from flare lights, H 2 S emanating 

 from foul soil, will increase the risk of rapid decompression by 

 lowering the vigour of the workmen, and thus the efficiency of the 

 pulmonary ventilation. 



THE EFFECT OF WATER PRESSURE ON BIOPLASM 



The sea covers 141 million square miles, or three-quarters of 

 the surface of the globe, and everywhere in this vast expanse, 

 from the cold Arctic and hot Red Seas, from the shallows and the 

 depths, the dredge has brought to view evidence of abundant 

 life. Up to 1865, and in spite of the results of soundings by John 

 and James Ross at 1800 m., naturalists considered the abysm of 

 the ocean just as barren of life as the highest mountain peaks. 

 While taking soundings for the Atlantic cable the naturalist 

 Wallich observed star-fish entangled by the sound brought up 

 from a depth of 6500 ft. Upon a piece of the broken Sardinian 

 cable, which was recovered from a depth of 2000 m., Milne 

 Edwards observed Polyps, Pectens, and even an oyster. These 

 animals had been living at a water pressure of 200 atm., and had 

 covered the cable with a crust doubling its thickness. 



The Channel, North and Baltic Seas, have a mean depth of 

 about 100 m. The Mediterranean mean, 1300 m. ; deepest, 4000 m. 

 The Atlantic mean, 3500 m. ; deepest, 5000 m. of? Cape Verd. The 

 Pacific mean, 4285 m. ; deepest, the fossa of Tuscarora off Japan, 

 8573 m. A column of water 10-33 m. high equals one atmosphere. 

 An animal living in the fossa of Tuscarora would therefore be 

 exposed to 857 atm, NO direct sunlight pierces to the depths, 



