EVENING DISCOURSES. 



G35 



oxygen The breathing is regulated by the concentration of acid (or the hydro- 

 gen ion) in the blood— carbonic acid is the natural end-product of muscular 

 metabolism; lactic acid is produced in the muscles when there is a deficiency 

 of oxygen. Deep breathing before the dive will wash out much of the carbonic 

 acid in the blood, owing to the increased ventilation of the lungs. The blood 

 and muscles, too, will be better oxygenated, and thus less lactic acid will be 

 produced during the submergence. If oxygen is breathed this will be still more 

 the case, as Martin Flack and I have shown. After deep breathing air tor 

 2 minutes we easily held our breath 2 or 3 minutes. After deep breathing 

 oxygen 5 minutes one of our subjects held his breath over 8 minutes and another 

 just over 9 minutes. Taking a deep breath and then holding it, J. M. pulled 

 up a 63 lb weight seventeen times in 23 seconds before he was compelled to 

 take another breath. After deep breathing air for 2 minutes he held his breath 

 while he pulled it up thirty times in 50 seconds; and after deep breathing 

 oxv^en for 2 minutes, seventy times in 85 seconds. Similarly after a deep 

 breath E A. E. held it while he ran 113 yards in 29 seconds; 150 yards 

 in 35§ 'seconds after deep breathing air for 2 minutes; 256 yards in 6?f seconds 

 after deep breathing oxygen for 2 minutes. S. E. ran on one breath 4/0 yards 

 in 110 seconds after deep breathing oxygen ! At the end he ran blindly, having 

 lost consciousness owing to the high concentration of CO, in his blood. ^ 



The high pressure of oxygen in the lungs enables one to hold one s breath 

 until the pressure of CO, reaches 10 to 11 per cent., while if the pressure of 

 oxygen is low a breath must be taken when that of the CO, reaches no more 

 than half this amount. A balance is struck between the relative pressures of 

 oxygen and carbonic acid. 



It is clear, then, that the naked diver can stay longer and do more efficient 

 work if he deeply breathed and filled his lungs with oxygen before each dive. 



I will demonstrate my little apparatus by means of which oxygen can be 

 generated from oxylithe (peroxide of sodium) and inhaled. Two blocks of 

 oxylithe are put in the metal box— the generator— and a pint of water in the 

 rubber bag. The mouthpiece of the bag is clipped and the water allowed to 

 enter the generator. Oxygen fills the bag, and a solution of caustic soda is 

 formed. The man breathes in and out of the bag. This invention allows 

 oxygen to be carried about, and has proved useful for mountain climbers who 

 at high altitudes suffer from oxygen want. 



Diving birds have double the normal volume of blood (Bohr), just as the 

 llama and the human inhabitant of high altitudes have more red corpuscles and 

 hemoglobin. Observations on the blood of naked divers would probably show 

 the same increase. 



The Mechanical Effects of Pressure on the Body. 



The body of the naked diver, at a depth of say 66 feet, is pressed upon 

 equally on all sides by the water, and by a pressure of 3 atmospheres ; for 33 feet 

 of water = 1 atmosphere. The gas in his lungs (and intestines) is compressed 

 into one-third of its volume, and that is the only effect of the pressure, for 

 the pressure is transmitted equally and instantly by the fluids of the body to 

 all parts, and as the fluids are practically incompressible the pressure has no 

 mechanical effect. 



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

 pressed air and breathes 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 dress, bell, or caisson. I will demonstrate 

 this on the model diver, diving bell, and caisson. Whether it be air or water 

 that uniformly presses upon the body, the tissue fluids transmit the. pressure 

 equally; and thus, although it is computed that an extra atmosphere means an 

 additional total pressure of 15,000 to 20,000 kilograms (40,000 lb.) on the body 

 of a man, no mechanical effect is produced. Living matter is a jelly containing 

 about 80 per cent, of water, and, like water, is practically incompressible. Since 

 attention was first drawn to compressed-air illness the larger number of medical 

 writers, ignorant of physical laws, have supposed that exposure to compressed 

 air mechanically alters the distribution of the blood, forcing it inwards and 

 causing a congestion, which is suddenly and dangerously altered on decom- 

 pression. 



