ENORMOUS PRESSURE OF GAS IN BLOOD 383 



subjected to such changes of pressure. Man can endure 

 without suffering an increase of pressure of the gases ii) 

 his body amounting to three or four times that to which 

 he is accustomed, as, for instance, when working in the 

 compressed air of " caissons." But the whale goes , sud- 

 denly to a depth at which the pressure is eighty times 

 that at the surface ! Then, too, man (and other terrestrial 

 animals), after being subjected (for instance, in a caisson) 

 to a pressure of four times that which exists on the free 

 surface of the earth, is liable to be killed by suddenly 

 passing from that high pressure into the ordinary air. 

 The gases dissolved in his blood expand like the gas jn 

 a bottle of soda-water when the cork is drawn, and. 14:^!; 

 bubbles interfere with the circulation of the blood ip the 

 finer blood-vessels (of especial importance being those of 

 the brain and spinal cord), and the serious illness rand the 

 death of workmen has frequently resulted from this cause. 

 Accordingly, the men who work in such " compressed 

 atmospheres " are now made to pass slowly through a 

 series of three chambers, in each of which the pressure is 

 diminished and brought nearer to that of the normal 

 atmosphere. By spending twenty minutes in each 

 chamber successively, the workman is gradually brought 

 to the pressure of the outer world, and his blood pre- 

 vented from "effervescing." But what must be the con- 

 dition of the gases in the blood of a whale which suddenly 

 rises from 400 fathoms to the surface ? The whale 

 suddenly goes, not from a pressure of four times thq 

 normal (" four atmospheres " as it is called), but frpm 

 eighty times the normal, to the normal pressure. 



Whales, and also seals, are provided with remarkable 

 special networksof blood-vessels in various parts of the body 

 (called " retia mirabilia " by the old anatomists), and aJso 

 with a thick layer of fat under the skin, the " blubber " 

 (some feet deep in a large whale), full of blood-vessels. 



