Oxygen and Carbon Dioxide Transport by Blood Containing Haemocyanin 



which deviate from hyperbolas, was suggested by Redfield to be due to 

 the blood pigment consisting of two or more components, each of 

 which react with oxygen independently of the others according to 

 Hill's equation, with different integral values of n. The idea that 

 undulatory curves can best be explained by postulating the presence 

 of more than one component seems plausible and is illustrated by an 

 experiment of F. H. McCutcheon 5 who obtained undulatory dis- 

 sociation curves from a solution containing haemoglobin of a tadpole 

 and of an adult frog. Moreover this point of view is substantiated by 

 the work of Svedberg et al 2 , Roche 3 and Brohult & Borgman 6 . On the 

 other hand the s-shape might as well be explained by assuming inter- 

 dependence between prosthetic groups of one molecule, especially as 

 the development of Adair's theory has in haemoglobin led to remark- 

 able results. 



Abandoning these interesting biochemical questions we shall now 

 turn to the comparative physiology of haemocyanin. The affinity for 

 oxygen of the haemocyanin in the blood of the king crab (Limulus) is 

 very great. The oxygen dissociation curve of the blood of the snail 

 Busycon (Figure 5) is also fairly steep. In both bloods the Bohr effect is 

 reversed. Whilst the first fact certainly will enable the animals to ac- 

 quire a fair supply of oxygen at low oxygen pressures provided, how- 

 ever, that their gills function effectively, the diffusion of oxygen into 

 the tissues must be limited by the low pressure at which it is delivered. 



It has sometimes been contended that a negative Bohr effect might 

 enhance the oxygen uptake, assuming that in a habitat poor in oxygen 

 considerable amounts of carbon dioxide might be present. Now 

 A. Krogh 7 has pointed out that relatively high carbon dioxide tensions 

 in natural water will only be found in a milieu where fermentative 

 processes take place, because even in carbonate-free water the carbon 

 dioxide tension would only rise to ± 5 mm if all the oxygen originally 

 present had been converted into carbon dioxide by respiration. As 

 Limulus (Figure 5) often burrows in the mud, the possibility at least 

 of measurable C0 2 tensions occurring in the respiratory milieu must 

 be admitted. The discharge of oxygen into the tissues must be still 

 more impaired by the negative Bohr effect. Of course it might be 

 argued that acquisition of a sufficient amount of oxygen by the gills 

 must have precedence, though this seems to me rather far-fetched. 



Turning to the properties of the blood of the edible snail (Helix 

 pomatia L) we have to deal with a still more enigmatic case. As has 

 been mentioned before, the oxygen dissociation curve is sigmoid in 

 the virtual absence of carbon dioxide, but it becomes more or less 

 hyperbolic at relatively low carbon dioxide pressures. It may be pointed 

 out that this change of shape is not caused by any permanent change 



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