RESPIRATION IN SOUTHERN WHALES 373 



took 20 min. to return to the surface. Shortly after conning up he was taken ill and died 

 in 7 minutes. Post-mortem examination showed black or very dark blood in the blood 

 vessels and large bubbles of air in the veins of Galen and the choroid plexus, in the right 

 ventricle of the heart, and in the veins covering the brain. Small vessels of the mesentery 

 attached to the gut were found full of nitrogen. It has been shown that the illness is 

 due to the accumulation of nitrogen in the vessels of the heart, certain blood vessels, 

 and the central nervous system. 



In order to see how far caisson sickness may be expected to be a danger to the normal 

 life of a Blue whale it will be convenient to summarize the main features of the illness 

 as it appears in man and other mammals, according to Hill. " The rate at which various 

 animals, and different organs of the same animal, become saturated and desaturated in 

 compressed air is proportional to the volume of blood relative to that of the tissues, and 

 to the velocity of the circulation." The volume of blood in the large Blue whale which 

 was weighed at Stromness in 1924 was 6-6 per cent of the total weight. The blood 

 volume in man is 4-9 per cent of the body weight (Haldane), in the horse 6-6, ox 77, 

 sheep 8-OI, and pig 4-6 (Ellenburger). No information is available as to the rate of 

 circulation in whales, though it is to be expected that as among land mammals, other 

 things being equal, the rate would be lower in a large animal such as a whale. The low 

 basal metabolism indicated above also suggests sluggish circulation. The heart of the 

 Blue whale according to two observations is about 0-59 per cent of the body weight, 

 the human heart is 0-41 per cent. These figures suggest, but by no means prove, that 

 the whale's heart is not notably larger or more powerful in proportion to the size of the 

 animal than the human heart. " If the activity of the circulation is great enough, the 

 excess of gas may escape by diffusion through the lungs without the formation of 

 bubbles" (Hill). For this reason small animals with rapid circulation are relatively 

 immune from the effects of decompression, while large animals are more liable to the 

 sickness. "When a liquid saturated with gas under pressure is suddenly decompressed 

 the excess of gas does not immediately come out of solution either by bubbles or 

 diffusion. This delay is specially marked in the colloidal body fluids." Hill goes on to 

 say that bubbles are not found in gland cells or muscular fibres (places of rapid circula- 

 tion of blood) but may, on the other hand, occur abundantly in the collections of body 

 fluids — bile, urine, and synovial and amniotic fluids. Bubbles are found most frequently 

 in the fat, because fat absorbs five times as much nitrogen as water and the circulation 

 through fat is relatively poor. "Oxygen bubbles are not a factor in caisson sickness — " 

 The fat in all cases of decompression is honeycombed like whisked white of egg. 



So far the probability that a whale will be liable to caisson sickness seems high. It is 

 hard to imagine that an animal which stayed submerged until the need for fresh air 

 became urgent should come to the surface so gradually as to allow the dissolved gases 

 to diffuse back into the lungs. The time required for desaturation is more than 20 min. 

 per atmosphere in man, so that, on the basis of human performance, if a whale were to 

 dive 100 m. and stay there for 15 min., by which time the supersaturation of the body 

 tissues might be half complete, it would, in order to avoid caisson sickness, have to 



