HEART, CIRCULATION, AND BLOOD 173 



blood, it must be remembered that most of our experimental material is 

 derived from dead specimens, and has consequently undergone certain 

 changes. Most investigators have been primarily concerned with the 

 oxygen affinity of the haemoglobin in, and the size and number of, the 

 red blood corpuscles. Their diameter in Cetaceans can vary between 7 -5 

 and 10-5 /i, (i.e. thousandth parts of a millimetre), depending on the 

 species. The biggest corpuscles are found in Sperm Whales (10-5 /x), 

 which hold the mammalian record. Other Cetaceans have red corpuscles 

 with an average diameter 8 -5 /x, which is rather higher than the general 

 average for all mammals taken together. Our own red blood cells have 

 an average diameter of about 7 -5 /x, but most other mammals have smaller 

 averages (horse 5-5 /x, goat 3-6 /x). The number of red cells per c.c. of 

 blood varies in Cetaceans between 7 and 1 1 million, the average being 

 about 9-5, again somewhat higher than the average for mammals of 

 comparable size. Thus in man, the average is 5, and in many other 

 mammals 6 to 7 million cells per c.c. of blood. Hence it is not surprising 

 that in 1 939 Knoll came to the conclusion that the ratio of red corpuscles 

 to blood plasma is much greater in Cetaceans than it is in man. 



Now^ the oxygen-carrying capacity of the blood depends not so much on 

 the total volume as on the total surface of all the red blood cells taken 

 together, for the greater the surface area the faster will the red cells be 

 able to take up oxygen in the lungs and to supply it to the tissues. Knoll 

 calculated that in Rorquals this total surface area is one-and-a-half times 

 and, in Sperm Whales, twice that in man - per c.c. of blood, of course. 

 Since, however, we have seen that the total quantity of blood expressed 

 as a ratio of the total size of a given animal does not differ greatly in 

 Cetaceans from that in other mammals, we can apply these figures to the 

 total volume of blood. 



Some scientists believe that the haemoglobin content of Cetacean red 

 blood cells is greater than it is in mammals in general, but others have 

 questioned this and ascribed the high figures recorded to experimental 

 errors. I myself investigated a great many Rorqual blood specimens 

 aboard the Willem Barendsz, and I never obtained values which differed 

 significantly from those for terrestrial mammals. However, the Japanese 

 biologist Tawara suggested in 1951 that blood pigments other than 

 haemoglobin may also play a part in transporting oxygen. 



Attempts have also been made to discover significant diffei-ences 

 between the oxygen-binding properties of the red blood cells of Cetaceans 

 and terrestrial mammals. In 1953 Burke submitted all the known data 

 to a critical examination, and suggested that all we could say with 

 certainty was that the haemoglobin of the porpoise and Bottlenose 

 Dolphin contains up to 19 per cent and that of the Fin Whale up to about 



