372 DISCOVERY REPORTS 



that a whale dived with its blood fully oxygenated and the lungs full of fresh air, the 

 fluid portion of the whale alone, 60 per cent of the total weight, or 73,200 1., could 

 dissolve 1793 1. of oxygen, or about 25 per cent more than the available volume, if the 

 partial pressure of oxygen were equal to i atmosphere. In other words, the volume of 

 oxygen taken down by the whale could be dissolved more than once over in the body 

 fluids before the partial pressure of the oxygen exceeded i atmosphere. In any case, as 

 Professor Krogh has pointed out, a large proportion of the oxygen in the lungs would 

 be used up before the whale reached any considerable depth. There is therefore no 

 theoretical obstacle to prevent the Sperm whale mentioned above from reaching the 

 depth of 900 m. at which it became entangled with the submarine cable. 



Excretion of carbon dioxide. The accumulation of carbon dioxide in the blood and 

 hence, by diff^usion, in the lungs will be considerable. In contrast to the conditions 

 underlying oxygen intake, the heightened pressure is in this case a disadvantage to the 

 whale. The eff'ect of carbon dioxide on the respiratory centre depends on the partial 

 pressure of the gas in the lungs and not on the percentage. A small percentage of 

 excreted carbon dioxide under a high pressure will have the same eff'ect as a large 

 percentage under a low pressure. Accumulation of carbon dioxide is bound to occur, 

 particularly in the blood, and, as will be shown later, considerable volumes of this gas 

 are found dissolved in body fluids as well as in the blood. The conditions which must 

 result from deep diving postulate a less delicate regulatory mechanism for the control 

 of carbon dioxide tension in the blood than exists in man and other land animals. The 

 respiratory centre, if it is similar in action to that of man, must be either adapted 

 to respond to a diff'erent range of carbon dioxide tensions or dependent entirely on 

 stimulation by oxygen shortage. One interesting consequence of stimulation by oxygen 

 shortage would be that if the stimulation began at 100 m. the whale's ascent to the sur- 

 face would cause greater and greater stimulation as the hydrostatic pressure decreased 

 and with it the partial pressure of oxygen in the lungs. 



Dissolved nitrogen and caisson sickness. The third consequence of hydrostatic 

 pressure on the whale is the passage of gases from the lungs into solution in the blood 

 and hence into the body generally. The physical solution of oxygen and carbon dioxide 

 in the blood is a minor phenomenon compared with the mechanism for taking these gases 

 into chemical combination. It remains therefore to consider the solution of nitrogen 

 and the inert gases (these latter being of minor importance). The transference of gases 

 from the lungs to the blood follows Dalton's Law of the solubility of gases. Blood dis- 

 solves about 1-2 vol. per cent of nitrogen from air at atmospheric pressure. For every 

 atmosphere increase in pressure the blood takes up another 1-2 vol. per cent. This pro- 

 cess in human blood is the basis of the trouble known to divers as caisson sickness, in 

 which nitrogen is dissolved in the blood under pressure and on decompression fails 

 to return to the air through the lungs if the diver's return to the surface is too rapid. 

 A summary of a typical case of caisson sickness is here abstracted from Sir Leonard 

 Hill's book on the subject (1912). A petty officer diving at Lamlash in 24I fathoms of 

 water (= 6 atmospheres) took 40 min. to reach the bottom, remained there 40 min., and 



