RESPIRATION IN SOUTHERN WHALES 



387 



Another method, in which the progress of nitrogen into solution was directly ob- 

 served, was used for determining the nitrogen capacity of the blood. The procedure is 

 as follows. A sample of blood whose initial nitrogen content is known is put in the gas 

 burette and a known volume of air is introduced over the blood. The exact volume of 

 air is measured wet as it stands over the blood after the upper stopcock has been sealed 

 with mercury. The burette is now inverted so that the air in the narrow graduated 

 portion is displaced by mercury and forced into contact with the blood in the bulb of 

 the burette. Vigorous shaking of the burette helps the mixing of the blood and air. At 

 intervals, the burette, in which the blood and air have been carefully kept at atmo- 

 spheric pressure, is restored to the vertical position and the volume of gas standing over 

 the blood is read. Inversion and shaking are repeated between readings, and at each 

 reading a trace of sodium hydroxide solution is run into the burette to absorb the carbon 

 dioxide evolved by the blood. All the oxygen in the air is absorbed in the first two 

 shakings. Before reading the volumes of nitrogen a trace of oxygen absorption mixture 

 is added to ensure absence of oxygen. Protocols of an experiment on these lines are as 

 follows : 



Sample no. 100: nitrogen content 1-12 vol. per cent; uncorrected volume 1-25 vol. per cent. 

 10 cc. of this blood enclosed in burette with 0-945 ^^- of ^ii" measured wet at 15° C. 



At the end of 35 min. the blood had absorbed 0-747 — 0-610 cc. = 0-137 cc.^ 



cent at room temperature and pressure. 

 So that the nitrogen in the blood was then 1-25 + 1-37 = 2-62 vol. per cent. 



1-37 vol. per 



The results of this experiment and others are shown graphically in Fig. 3, where the 

 volume of nitrogen absorbed in addition to the volume already in solution have been 

 plotted against time. It is of course to be realized that the means used for mixing the 

 blood and air were inefficient, and that under ideal conditions of mixing the absorption 

 of nitrogen would in all probability proceed much faster. 



While different samples of blood give different nitrogen capacities, the nitrogen 

 capacity of any one sample is fairly constant. For example, the nitrogen capacity of 

 no. 108 was estimated four times: (i) starting from the initial nitrogen content of 

 I -08 vol. per cent (uncorrected), (2) after evacuation, (3) after a second evacuation and 

 treatment with pure nitrogen instead of air, (4) after removal of nitrogen after (3) by 

 a third evacuation. The nitrogen capacities were respectively 2-32, 2-34, 2-66, and 2-36. 

 The higher capacity in (3) is the result of using pure nitrogen, and the difference be- 

 tween it and the other capacities is approximately the volume of extra nitrogen which 

 would go into solution in water when the partial pressure of the gas was 760 instead of 



