CHAPTER 9 



Respiratory Functions of Body Fluids 



IN MOST ANIMALS which havc a circulatory system (insects excepted) 

 there is a pigment in the blood or body fluid which is capable of 

 combining with oxygen. In higher mammals, for example, oxygen is 

 dissolved in the plasma to the extent of 0.3 volumes per cent, and in whole 

 blood to the extent of 0.24 volumes per cent. Actually, arterial blood contains 

 19 volumes per cent of oxygen; 98 per cent of the oxygen in the blood is com- 

 bined with hemoglobin. In this chapter we shall consider the role of blood 

 pigments in oxygen transport under usual physiological conditions and at 

 times of hypoxic stress. All blood pigments contain some metal in an organic 

 complex. Good summaries of the literature are given by Redfield,^-*^- ^^^ 

 Barcroft,"^ and Florkin.^o- ^2. 53 



DISTRIBUTION OF PIGMENTS 



Hemoglobins. The most common of blood pigments are iron-containing 

 red pigments, the hemoglobins; their protein components differ considerably, 

 and hemoglobins have arisen in many unrelated animal groups. The molecules 

 of invertebrate hemoglobins are much larger than those of vertebrate hemo- 

 globins, and for this reason invertebrate hemoglobins have been called eryth- 

 rocruorins.^^^ However, the prosthetic groups in all hemoglobins are similar 

 (porphyrins), and the proteins differ even from species to species of verte- 

 brates; hence it seems preferable to apply the name hemoglobin to all of the 

 red, iron-containing porphyrin-proteins. 



The distribution of blood hemoglobin and of other pigments is given in 

 Table 48. Hemoglobin is found in all vertebrates, although it is absent from 

 some transparent young fish (e.g., eels), which have colorless erythrocytes.^^^ 

 Hemoglobin is lacking in Amphioxiis; it has been reported from one pro- 

 chordate— DiscogZossws.^^^ 



Among the annelids, hemoglobin (erythrocruorin''^*') is found in the plasma 

 of many oligochaetes— Liiwfcnciis and others, in some leeches— as Hirndo, and 

 in many polychaetes— such as Nereis and Arenicola (Tables 48 and 49). In 

 some other polychaetes, Glycera, for example, hemoglobin is contained in 

 nucleated corpuscles. In general, those annelids whose hemoglobin is irj 

 solution in the plasma have a closed circulation, whereas those with the pig- 

 ment in cells have a poorly developed vascular system and the pigmented 

 cells are in coelomic spaces only.^"'- In two genera, Terebella and Travisia, 

 hemoglobin is found both in solution in the blood plasma and in cells in the 

 coelomic fluid. 



Hemoglobin occurs in a few molluscs, in the plasma of the snail Planorhis, 

 and in corpuscles of the clam Area (Table 48). Hemoglobin appears sporadi- 



290 



