270 



LOADING UP 



bed of the sea. The volume of gas in solution in the body is at 

 once reduced to 1/3, viz.: 0-005 c.c. per gram. At the same time 

 the blood in the lungs has its content of nitrogen reduced from its 

 normal value of 0-87 c.c. per 100 c.c. of blood to 0-29 with almost 

 immediate restoration to the normal figure. The litre of blood 

 in the capillaries of the lungs would now have in solution three 

 times the weight of nitrogen as under normal pressure. When 

 the blood arrives at the tissues, partition of its load will take 

 place. Each gram of tissue has a deficit of 0-01 c.c. of nitrogen, 

 and nitrogen will pass from blood to tissue till each gram of tissue 

 contains the normal value of 0-015 c.c. per gram. This value 

 will not be reached at once, because the very acquisition of 

 nitrogen by the tissue implies the loss of nitrogen by the blood. 

 The blood then returns to the lungs for a fresh charge, which it 

 again shares with the tissues, and so on. Haldane calculates 

 that somewhere about five hours are required before the body is 

 completely saturated with nitrogen after any change of pressure, 

 i.e. till the partial pressure of nitrogen in the tissues corresponds 

 with its partial pressure in the blood and so to its partial pressure 

 in the alveolar air. 



If we consider the amounts taken up by the various tissues we 

 may arrive at some conclusion as to the mechanics of the processes 

 of saturation and desaturation. The average working man 

 weighs 70 kg., of this amount 15 per cent, or 10-5 kg. is fat or 

 fatty material ; 5 per cent, or 3-5 kg. represents the amount of 

 blood ; while the earthy constituents of bone (about 3 per cent.) 

 may be neglected. 



TABLE XLVIL 



DISTRIBUTION OF NITROGEN IN THE TISSUES OF MEN WEIGHING 70 KG. 



Blood, as we have seen, can take up in simple solution about 

 0-87 c.c. of nitrogen for every 100 c.c. Taking the specific 

 gravity of blood as 1 -06 we may consider that about 30 c.c. of 



