HEART, CIRCULATION, AND BLOOD I55 



animals reacted so violently that some of the investigators nearly lost 

 their lives. In 1957, when President Eisenhower had recovered, White 

 made a fresh attempt, this time using a helicopter and a gun that fired two 

 electrode harpoons simultaneously. But once again he failed to register 

 the heartbeat of the Grey Whale, one reason being that the animals were 

 frightened away by the cvuTents of air which the helicopter churned up. 

 However, it has been announced that further attempts will be made 

 shortly. 



In any case. White did manage to take the Beluga's pulse. Now, the 

 pulse of an animal swimming about with three harpoons in its body 

 might be expected to be exceptionally high and irregular, as would our 

 own in similar circumstances, but White measured a regular 16 to 17 

 beats a minute - remarkably little, we might think, for an animal weighing- 

 some 22 cwt, particvilarly if we bear in mind that elephants were found to 

 have an average rate of 30 beats a minute. Actually, the bigger an animal 

 the slower is its pulse. Thus, horses have 40 heartbeats a minute, pigs and 

 humans 70, cats 150, hedgehogs 300, and mice 650. From these figures, 

 we should expect the Beluga to have a pulse of roughly 35. Now, all White's 

 electrocardiograms were taken while the Beluga was swimming under- 

 water, and we know that the pulse rate of all animals drops when they 

 dive. Thus our own pulse rate falls from 70 to 35, and in aquatic mammals 

 the decrease is far greater still. Irving and his colleagues established 

 experimentally that, while diving, the pulse of a beaver drops from 1 40 

 to 10, that of a penguin from 240 to 20, and that of a seal from 120 to 10. 

 In applying their work to Cetaceans, they had an easier task than White, 

 since they experimented with tame Bottlenose dolphins in the Marineland 

 Seaquarium (Florida). They managed without much trouble to apply 

 electrodes to these animals and also to some others in the bay, and found 

 that their pulse rate was 1 10 beats a minute at the surface and 50 beats a 

 minute below; it began to increase just before the animal surfaced. 



Irving and his colleagues think that the drop in the pulse rate during 

 a dive is due to the fact that part of the blood circulation is shut off. In 

 the last chapter, we saw that, in a dive, very little oxidization may occur 

 in the muscles, and that more oxygen is consequently made available for 

 the organs which cannot do without it: the heart and the brain. How 

 sensitive these organs are to oxygen deficiencies can best be seen from the 

 fact that, in man, while the blood supply to all the muscles can be cut off 

 for some 15 minutes, and that to the arms and legs for a few hours, without 

 appreciable damage, the heart would suffer serious injury after a much 

 shorter time, and the brain after only 3 to 5 minutes. Fifty per cent of 

 human beings would die after the blood-flow to the brain had been 

 stopped for 2-3 minutes. 



