324 Comparative Animal Physiology 



hemoglobin remains reduced or when it is poisoned by CO and the hemoglobin 

 can hardly be functional."'' *'-^ 



Claims have been made that in the snail Planorhis and the lugworm Areni- 

 cola hemoglobin may function as an oxygen store to be used only in times of 

 anoxic stress. In the absence of COo the ti/o sat of Planorhis blood is higher 

 than the tj/o sat of Chironomns and Tiihifex blood, 7.4 mm. at 20°^°^ and 1.9 

 mm. at 17°.''^' Carbon dioxide decreases the affinity for oxygen (ti/o sat=8.9 

 mm. at 17° in 1 per cent COo).*'^ In vivo the oxyhemoglobin bands disappear 

 at water oxygen of 25 mm. Hg/^*^ but the blood remains saturated with oxygen, 

 and skin breathing with the oxygen carried in solution in the blood provides 

 sufficient oxygen for the animal down to a tension of 7.7 per cent O2 (54 mm. 

 Hg).'"'"' In the range 7.2 to 3 per cent Oo the snails frequently came to the 

 surface for lung breathing and the hemoglobin was not completely saturated, 

 whereas below 3 per cent they were at the surface continuously. In the pres- 

 ence of CO below 3 per cent Oo the snails became very sluggish, and at 1 per 

 cent O2 they floated outstretched on the water. Hence the use of the lung 

 and reduction of hemoglobin go together. From the data of oxygen capacity of 

 the blood (2.4 times that which could be carried in solution), the blood volume 

 (0.58 cc./g. body wt.) and the oxygen consumption (0.026 cc./g./hr.) 

 Borden'^ estimated that the oxygen held by hemoglobin would last 18 minutes 

 of anoxia and Leitch'*''' estimated it would last 3 minutes. It appears that the 

 storage function is negligible, that hemoglobin functions in oxygen transport, 

 particularly at water oxygen of 25 mm. and below, and that the tissue oxygen 

 tension is not so low as in Chironovnis and Tiihifex. 



In Arenicola the hemoglobin is reduced at 1-3 mm. Hg (1.8 mm.*'*^) and is 

 completely saturated at 5-10 mm. O2. The oxygen capacity is about one-sixth 

 that in man.'^ COo shifts the oxygen dissociation curve to the right.'-'' **" In the 

 burrows of Arenicola the oxygen becomes depleted at low tide.'-*' ^^ At such 

 times the tension in the tissues must be much reduced. If the hemoglobin u^ere 

 to be completely reduced, enough oxygen would be made available for 21 

 minutes at the usual rate of Oo consumption. In nature the worms survive 

 periods of about 3 hours when the oxygen in their tubes is negligible. The 

 state of the hemoglobin in living worms is not known, but the hemoglobin 

 must unload oxygen to the tissues when their O2 tension is below 2 mm. If 

 the tension at the gills is greater, oxygen will be taken up. At low tensions the 

 worms may well resort to anaerobic metabolism. In the absence of carbon 

 monoxide experiments and measurements of the saturation of hemoglobin in 

 vivo, judgment must be withheld regarding the function of the pigment at 

 high oxygen tensions. 



In study of the worm Urechis Redfield and Florkin'-^ found oxygen capa- 

 cities of 2.6 to 7.2 volumes per cent in different individuals; there was little 

 effect of CO2 on the oxygen dissociation curve (Fig. 69). The hemoglobin 

 showed an unloading tension of 12 mm. O2 at 8.6 mm. CO2. The worm lives 

 in mud tubes in the intertidal zone, and at low tide the oxygen in the burrow 

 is greatly reduced. RcdHeld and Florkin calculated that when the water 

 reached an O2 tension of 14 mm. the requirements of the animal could be met 

 for only about 15 minutes by the oxygen dissolved in the coelomic fluid and 

 in the water contained in the respiratory region of the gut, whereas the extra 

 oxygen from the blood pigment would permit survival for a further 55 minutes. 



