374 DISCOVERY REPORTS 



return slowly to the surface during a period of at least loo min., which is contrary to 

 observation. 



The influence of fatness on the liability to caisson sickness is marked in land mammals 

 because of the high solubility of nitrogen in fat mentioned above. Boycott, Damant and 

 Haldane (1908) have tested guinea-pigs and concluded that fatness increases thesuscepti- 

 bihty to death from caisson sickness. The coefficient of solubility of the watery part of 

 the body may be taken to be 0-9 per cent and of the fatty part about 5-0 per cent. Man 

 contains on the average 66 per cent water and 1 5-20 per cent fat. The fat content of 

 a Blue whale including internal fats varies seasonally but is seldom more than 24 per 

 cent of the weight and frequently as low as 20, so that whales are in proportion little 

 fatter than man. 



The Blue whale whose weight has been considered above contained 6o-o per cent 

 water and 2275 per cent fat. The weight was 122,000 kg. The watery part, 73,200 kg., 

 would dissolve 658-8 1. of nitrogen from air at atmospheric pressure, while the fat, 

 27,755 ^§-> would take up 1387-7 1. The total uptake of nitrogen is therefore 2046-5 1. 

 at atmospheric pressure, and in addition the same amount can be absorbed from the 

 air in the lungs for every atmosphere of compression which the whale undergoes. The 

 vital capacity of this whale was estimated conservatively at 3050 1. of air, of which 

 2440 1. would be nitrogen, so that if the whale stays submerged, even at a depth of 

 10 m., at which i extra atmosphere pressure is appHed over and above atmospheric 

 pressure, all the nitrogen in the lungs will eventually disappear into solution in the body 

 fat and fluids. The nitrogen from one breath would obviously be insufficient to over- 

 charge the blood ; but the cumulative effect of successive inspirations followed by sub- 

 mersions would be to overcharge the blood, so that in the event of the whale's electing 

 to stay at the surface longer than the instant which is usual caisson sickness might 

 supervene. After a certain number of breaths at the beginning of the whale's hfe, there 

 would be an equilibrium established between the nitrogen in the blood and the nitrogen 

 in the lungs at the pressure which represented the average depth of submersion. After 

 a time only a little nitrogen would go into solution if the whale dived a little deeper than 

 usual, or only a little gas would come out if the dive were shallower than usual, but 

 there would still be the same danger from decompression bubbles if the whale hngered 

 at or near the surface. 



GAS ANALYSES 



The theoretical conditions of a whale's respiration construct a scheme of life which 

 condemns the whale never to delay at or near the surface on penalty of caisson sickness. 

 Actually a whale can linger at the surface, as for instance when suckling a calf, and an 

 explanation of this is to be found in the condition of gases in solution in freshly killed 

 whales. It will never be possible to know everything on this subject of whales' respira- 

 tion for obvious reasons, but, just as the life history of Blue and Fin whales has been 

 reconstructed in considerable detail from examination of their carcasses, so the study 

 of the gas contents of whales' body fluids has thrown light on respiratory activities. It 



