Respiratory Functions of Body Fluids 293 



globin is found with bacteria in the root nodules of certain leguminous plants, 

 where it appears to function in nitrogen hxation.'-*" 



Chlorocruorin. In three families of polvchaete worms, particularly the 

 Sabellidae and Serpulidae, there is a pigment, called chlorocruorin, which 

 contains iron in a different porphyrin from hemoglobin and which is green 

 in color in dilute solution. 



Hemerythrin. A third iron-containing pigment, hemerythrin, occurs in 

 the polychaete worm Magelona, in the sipunculoid worms Sipuncidus and 

 Phascolosovia, and also in the brachiopod Lingula. Hemerythrin is found in 

 corpuscles and is brown in color. The corpuscles of Magelona are non- 

 nucleated. Hemerythrin does not contain a porphyrin, and hence is very 

 different in chemical properties from hemoglobin and chlorocruorin. 



Hemocyanin. The pigment which is next in importance to hemoglobin, 

 judged by its distribution, is hemocyanin. This is a copper-containing protein 

 which occurs in cephalopod molluscs, some gastropods, higher crustaceans, 

 Limidus, and a few arachnids. The concentration of hemocyanin roughly 

 parallels that of copper in the blood. Hemocyanin is a protein without any 

 porphyrin group. 



Miscellaneous Pigments. Several other blood pigments should be men- 

 tioned, even though their respiratory function has not been demonstrated. In 

 the body fluid of a mussel. Pinna, there is a brown pigment, called pinnaglobin, 

 which contains manganese. '^^ The body fluids of some ascidians contain a 

 pigment which is a vanadium chromogen.'^^'' ^-'^ In certain cells, the eleocytes 

 of the coelomic fluid of sea urchins, there is a red pigment, echinochrome. This 

 contains little iron, has a low oxidation potential, and is probably enzymic in 

 function.-- Crescitelli-'' identified by its absorption bands a pigment which he 

 called molpadin in the holothurian Molpadia. 



SIZE AND COMPOSITION OF ERYTHROCYTES 



The hemoglobin of vertebrates is contained in corpuscles called erythrocytes. 

 In higher mammals the erythrocytes constitute 40 to 50 per cent of the total 

 blood. Mammalian erythrocytes are circular (except in the Camellidae), non- 

 nucleated, and biconcave. Erythrocytes of most other vertebrates are elliptical, 

 nucleated, and double convex. The number of erythrocytes per cu. mm. 

 varies with the size of the cells. Table 50 gives the size and red cell count for 

 a number of representative species. In man, the count is higher in infants 

 (6,000,000/mm.-0 than in adults (males 5,000,000 and females 4,500,000/ 

 mm.^). The number of red cells is higher at high altitudes than ai sea level. 

 Data collected by Talbot in the Andes showed that the normal red cell count 

 of most persons living at altitudes greater than 10,000 ft. was over 5,500,000 

 per cubic millimeter, with great individual variability.-^- Hemoglobin content 

 of the blood parallels the increase in red cell count at high altitudes. 



Table 50 shows that in general the red cells of mammals are smaller and 

 more numerous than the red cells of lower vertebrates. The largest red cells 

 occur in the Amphibia, particularly in such animals as Amphimna. The 

 oxygen-combining capacity of the blood is proportional to the total amount of 

 hemoglobin, rather than to the red cell count. Table 50 gives the hemoglobin 

 content of the blood of a number of animals. The small number of red cells 

 in lower vertebrates is partly compensated by larger cell size. 



