174 WHALES 



14 per cent of oxygen. These figures are of the same order of magnitude 

 as those fovmd in terrestrial mammals, in the case of which they fluctuate 

 between 1 1 per cent and 24 per cent. The only striking differences were 

 found in seals, for which the figure was 29 per cent. All these remarks 

 bear out our argument in Chapter 4, viz. that no special reserves of 

 oxygen are stored in the blood during diving. 



The Cetacean muscles, on the other hand, are known to contain 2-8 

 times as much myoglobin (muscle haemoglobin) as those of terrestrial 

 mammals, and to have an affinity for oxygen that far surpasses that of 

 normal haemoglobin. Now we understand why the red blood corpuscles 

 of Cetaceans cannot have an excessive affinity for oxygen, since, other- 

 wise, they would be unable to surrender enough of this gas to the muscles 

 which need large reserves of it in dives when their oxygen is cut off. This 

 is probably also the reason why the haemoglobin of the deepest divers 

 absorbs the lowest percentage of oxygen, and so shows the greatest 

 difference from myoglobin. Low oxygen capacity of the blood cells 

 and high oxygen capacity of the muscles obviously meet the needs of 

 Cetaceans and other diving mammals admirably. Hence, the main 

 characteristic of Cetacean blood cells is their exceptionally large surface 

 area which enables them to effect gaseous exchanges very speedily - a 

 reasonable arrangement if we consider how little time Cetaceans generally 

 spend at the surface, and in how short a time the oxygen reserv^e in their 

 muscles has to be replenished. Their blood must therefore be considered 

 not so much an oxygen reservoir for diving, as a quick means of transport- 

 ing oxygen when surfacing. 



To complete the picture, we must say something about the other blood 

 cells of Cetaceans. Scientists have found nothing unusual here, except an 

 increased proportion of eosinophil leucocytes in the blood. This pheno- 

 menon is not yet understood, but in any case it must be remembered that 

 practically all the blood examined was taken from animals which were 

 killed after a desperate struggle and which, moreover, must have lost vast 

 quantities of blood, with consequent changes in the total blood picture. 

 This may also explain why some specimens were found to contain an 

 unusually high percentage of normoblasts. If we remember that the blood 

 picture in pigs can change significantly after the animals have spent only 

 one hour in a cattle truck, it seems almost certain that the blood of 

 Cetaceans captured after a long chase must undergo significant changes also. 



No discussion of the vascular system and the blood would be complete 

 without some mention of the spleen, an organ which plays an important 

 part in the circulation of all mammals. However, what precisely this part is, 

 is no clearer today than it was in the day of Claude Bernard, the great 

 French physiologist who, while examining a candidate, asked him to 



