Respiratory Functions of Body Fluids 305 



globin, but rather absorbs broadly. It shows much colloidal scattering (Tyndall 

 effect), and when this is subtracted from the total absorption it is seen that 

 maximum absorption for several species lies between 550 and 600 m/i,. In 

 addition there is absorption in the ultraviolet which may be associated with the 

 prosthetic group (see Redfield^-^ for discussion). 



Measurements of the sedimentation constants made with the ultracentrifuge 

 indicate that the molecule of hemocyanin may occur in several different sizes. ^^ 

 As shown in Table 53, two genera of the Malacostraca, Pandahis and Pal- 

 inurus, have a sedimentation constant of 16, whereas two others, Nephrops 

 and Homariis, have a sedimentation constant of 23; Astacus, Cancer, and 

 Carcinus show both of these sedimentation constants; that is, the molecules 

 are of two aggregation sizes. The molecular weight corresponding to the 

 sedimentation constant of 16 is 360,000, and that corresponding to the constant 

 of 23 (Hoviarus) is 640,000. Hemocyanin from Liniulus shows four sedimenta- 

 tion constants, the principal one corresponding to a molecular weight of 

 1,300,000. In general, the sedimentation constants of molluscan hemocyanins 

 are much higher than those of hemocyanins of arthropods. For example, the 

 molecular weight of hemocyanin is 2,785,000 in Octopus, 3,316,000 in the 

 squid, and 6,630,000 in a snail (He/ix).'^'* Hemocyanin, which always occurs 

 free in solution in the blood, has much larger molecular weights than the pig- 

 ments which are contained in corpuscles. There is some evidence (see Red- 

 field^-^ for summary) that the large molecules are aggregates of units each 

 containing 8 atoms of copper (4 oxygen equivalents). 



Many animals having hemocyanin as the blood pigment nevertheless have 

 myoglobin in their muscles. The odontophore retractor of Bxisycon, for 

 example, contains more myoglobin than does dog heart muscle.^ 



Vanadium Chromogens. Many ascidians are rich in a green pigment con- 

 taining vanadium, of which at least 80 per cent is in the blood. ''^^' ^^^' The 

 vanadium content varies from 0.04 per cent of the total dry weight in Ciona 

 intestinalis to 0.186 per cent in Ascidia ntentida. This is a remarkably selective 

 concentration of vanadium from sea water, which contains only 0.3 to 0.6 

 milligrams per cubic meter. Webb^'*'' found that among the various families 

 and genera of ascidians, vanadium is lacking in the more primitive Larvacea 

 and Thaliacea; it is present in the plasma of the Cionidae and Diazonidae and 

 in special blood cells, vanadocytes, in several families, including Ascidiidae 

 and Perophoridae, and apparently the element has been lost in the higher 

 groups, such as Styelidae, Molgulidae, and Clavelicinidae. 



The vanadocytes are about 8 micra in diameter and constitute 1.2 per cent 

 of the total blood volume or 60 per cent of the total blood cells in some 

 Ascidiidae.^^*^ The vanadium is present in these cells as a chromogen which 

 apparently consists of a chain of pyrrol rings; it is not a protein and it is not 

 a porphyrin compound. The vanadium is kept in a reduced form by the. 

 presence of a high concentration of H0SO4. Titration of the whole blood 

 showed a total acidity of 0.022 N and that of cytolyzed corpuscles showed an 

 acidity of 1.83 N or 9 per cent H2S04.'^'''' The oxidation potential of the 

 vanadium chromogen is too low for it to be of use physiologically in respiration. 

 Furthermore, various reducing agents are not oxidized more rapidly by air 

 in the presence of vanadocytes than in their absence. Henze**" suggested that 

 the vanadium might be necessary for the synthesis of tunicin, the material of 



