98 TRANSPORT OF THE RESPIRATORY GASES 



in the transport of oxygen from the respiratory organ and its 

 liberation at the tissues where the oxygen tensions are low is 

 due to the effect of pH and CO 2 content on the form of the dis- 

 sociation curve. Fig. 27a shows this difference for the bloods of 

 a fish and a dog. The effect of an increase in CO 2 concentration 

 is to shift the curves to the right — the so-called 'Bohrshiff. This 

 has the important effect of increasing the amount of oxygen 

 liberated from the haemoglobin in tissues where the carbon 

 dioxide content is high. The curve indicating the dissociation 

 of the blood pigment in the body between the lung and tissues 

 is intermediate between the two curves shown in fig. 27a. It is 

 apparent that there is an increase in the steepness of the curve 

 over the effective range which produces a greater liberation of 

 oxygen for a given difference in ambient oxygen tension. The 

 Bohr shift is present in most forms having haemoglobin or 

 haemocyanin as a respiratory pigment and in nearly all cases 

 the blood eventually becomes 100% saturated at the higher 

 oxygen tensions. In fish bloods, however, the effects of CO 2 or 

 pH are very much more marked than in any other animals. They 

 may be so great that the blood does not become 100 % saturated 

 even at greatly increased oxygen tensions. In some deep-water 

 fishes it has been shown that a partial pressure of oxygen greater 

 than 140 atmospheres may be required to saturate fully the 

 blood with oxygen. This effect, that the blood does not become 

 100% saturated except at extremely high oxygen pressures, is 

 known as the Root effect. It may have an important function in 

 the liberation of oxygen in the swimbladder of many teleost 

 fishes. Thus an increase in CO2 concentration within the gas 

 gland (p. 33) will lead to the liberation of O2. Such a mechanism 

 cannot be involved in fish like the long-nosed eel because the 

 pressures at the depths they inhabit (fig. 27d) are so great that 

 their haemoglobin remains 100% saturated even at high CO2 

 tensions (eee pH 6). 



In contrast to the fishes living in water of high oxygen content, 

 those which occupy swamps and other regions of high CO 2 

 tensions have haemoglobins which are relatively insensitive to 

 the CO2 (fig. 27b). Most of these forms, e.g. the electric eel, have 



