Respiratory Fiinctiofis of Body Fluids 333 



animal groups. The buffer value of the blood is given by the ratio Bl ICO3, 



pH 

 i.e., the change in pH with CO:-. It can also be shown by a titration curve of 

 blood (Fig. 85). The buffering power ol hemoglobin of different bloods is 

 similar and the hemoglobin buffering is correlated with the oxygen capacity. 

 In reptiles the CO2 content of the blood is high, 2-3 times that of mammals 

 (Table 58), but most of it is carried in plasma as BUCO.j.-'-*- '^^ The buffering 

 capacity of the trout and mackerel is high, whereas that of the carp, toadhsh, 

 and skate is low.'" I he buffer value of the serum proteins is greater per gm. of 

 protein in the skate and crocodile than in mammals.^-" 



There is much variability in the effect of oxygenation of hemoglobin on the 

 C02-combining power. In man, at 40 mm. Hg of CO2, venous blood combines 

 with 52 and arterial blood with 50 volumes per cent of COj. In the crocodile 

 the change in acid strength of hemoglobin when oxygenated is greater than it 

 is in man.'^-^ In the skate, however, there is no difference between the COo 

 dissociation curve of oxygenated and that of deoxygenated blood.'""' In the 

 tautog oxygenation decreases the CO^combining power at low COj tensions, 

 but above 50 mm. the curves for oxygenated and for deoxygenated bloods are 

 similar. After hemolysis, however, the deoxygenated blood combines with 

 more CO2 at all tensions.'"' In general, those animals in which CO2 increases 

 the oxygen affinity are the ones in which oxygenation decreases the C02- 

 binding power. These effects depend on protein differences which are not 

 understood. 



Buffering in Invertebrates. Among invertebrates most of the buffering 

 appears to reside in blood proteins, and the principal proteins are respiratory 

 pigments. In Urechis, for example, the plasma of the coelomic fluid has 

 practically no buffering capacity, but the corpuscles are capable of buffering to 

 about the same degree as the corpuscles of a vertebrate of similar oxygen 

 capacity.'--' The coelomic fluid of the sea urchin, which contains little protein, 

 has very little buffering power (Fig. 85)."' 



Redfield and his associates'-'' have shown in a series, of papers that in those 

 bloods which contain hemocyanin most of the buffering is due to this pigment. 

 In Livndus, for example, phosphates are negligible, but purified hemocyanin 

 can bind 1.6x10^'' mols of acid per gram of protein, and in the presence of 

 blood salts hemocyanin can bind much more. I his buffering capacity is similar 

 to that of hemoglobin. The titration curve of hemocyanin in the presence of a 

 salt mixture like the blood salts is essentially similar to the titration curve of 

 serum of LnuiiZiis.'-*' This titration curve shows the presence of several acid 

 and base binding groups. In Helix the blood is less well buffered than in 

 Liniidiis, but it is buffered better in summer than in the winter."'^ 



In Helix, Octopus, and Hoinarus oxygenated hemocyanin binds more COo 

 than does deoxygenated hemocyanin. 



In animals with calcium-containing shells, some molluscs and crustaceans, 

 an important source of buffer is the shell. This has been discussed in Chapter 3. 



Carbonic Anhydrase. Carbonic anhydrase is widely distributed in the 

 animal kingdom. ■*'• ''^' ''• ■''^' '^'^ None has been found in the sponges, but 

 some is present in coelenterates, particularly in the tentacles. Carbonic an- 

 hydrase is found in coelomic fluid of Sipiwcuhis and Arenicola but not in that 

 of most other invertebrates.''' A rich suppK of this enzyme is present in the 



