320 Ccnnparative Animal Physiology 



in the blood, oxygen is forced out into the swim bladder and the fish may be 



^' Hemoe'lobin Function in Invertebrates. The function of blood pigments 

 is in doubt for manv invertebrates. The following sorts of evidence are useful 

 in judging whether a respiratory pigment functions in oxygen transport: CO 

 the position of the oxygen dissociation curve, i.e., whether the pigment loads 

 and unloads under physiological conditions at tensions corresponding to those 

 at the respiratory surface and in the tissues; (2) the effect of CO,, i.e., whether 



% SATURATION WITH OXYGEN 



Fig. 75. Oxygen dissociation curves of maternal and fetal blood of goats. Data for 

 goat pregnant 18 weeks, 2 days. Broken lines indicate limits of normal adults. From 

 Barcroft et al.^" 



the addition of CO, facilitates unloading of O, at a given tension and, con- 

 versely, whether loss of CO, aids the loading of Oo at respiratory tensions; (B) 

 the oxygen capacity of the blood and the difference between the Oo combined 

 and uncombined with pigment, as compared with the oxygen requirement of 

 the animal; (4) differences in Oo content in arterial and venous blood indi- 

 cating utilization; (5) effect on oxygen consumption of the animal of poison- 

 ing or of inactivating the pigment at different oxygen tensions. In invertebrates 

 in which the function of blood pigments is uncertain it is not always possible 



