38o DISCOVERY REPORTS 



total carbon dioxide. This average does not include the combined carbon dioxide in 

 sample 56, which is taken to be exceptional. 



The graph shows that twenty-six out of the fifty-six gas contents are grouped round 

 a partial pressure of 140 mm. of mercury, or roughly twice that of the human controls, 

 three agree approximately with human tensions, and the remainder are spread fairly 

 evenly over tensions ranging from 240 to 540 mm. of mercury. It must be remembered 

 that the tensions of carbon dioxide in the lungs which gave rise to these volumes of gas 

 in the urine through the medium of the blood can have originated in one of three ways : 

 by accumulation of carbon dioxide in the lungs during a long dive, or by a compression 

 of the carbon dioxide, or by a combination of the two. It is not therefore possible to 

 judge the depth of diving which caused a given tension of carbon dioxide unless the 

 duration of the dive is also known. But it is perhaps significant that such a large 

 accumulation of gas per se would derange the hydrogen-ion concentration of the blood 

 and other fluids, while increased pressure would have the effect of transmitting carbon 

 dioxide through the blood to the urine at high tension, but without seriously altering 

 the reaction of the blood. It is therefore likely that the carbon dioxide tensions implied 

 by the condition of the urine are an indication of the depth to which the whale dived 

 during the last half hour or so of its life. The group mentioned above which centres on 

 140 mm. of mercury in all probability represents the general state of carbon dioxide 

 conditions in the body, and it suggests a habitual depth of submersion of between 20 

 and 30 m. The remaining whales showing tensions higher than 140 mm. of mercury are 

 those which dived deep and long in their efforts to escape from the harpoon, while the 

 group of three low tensions is evidence of a small minority which had been basking or 

 feeding at the surface for some hours previous to capture. (A small proportion of whales 

 are killed by the first harpoon without a struggle.) 



The interpretation of these figures must be open to suspicion because urine is con- 

 stantly being generated and excreted and hence reflects only the whale's recent activities. 

 A stationary body of fluid, such as allantoic fluid, which will be considered later, shows 

 with more precision the whale's normal or habitual condition. 



The salt contents of these samples of urine, some of which are recorded in column 6, 

 Table I, show considerable variation. That there appears to be some relation between 

 the dissolved carbon dioxide and the salinity of the solvent is shown in Fig. 2, from 

 which it may be concluded that to some extent the salinity is inversely proportional to 

 the volume of dissolved gas. These results may indicate that the presence of carbon 

 dioxide at high pressures in the body of the whale is accompanied by an increased ex- 

 cretion of urine and that this diuresis serves to carry away considerable quantities of 

 carbon dioxide which would otherwise discommode the whale. It is impossible to say 

 whether this diuresis, which can be said to coincide with times of high external pressure, 

 is a direct result of increased difference between the blood pressure in the glomeruli and 

 the pressure in the ureter, giving rise to increased flltration, or whether it is caused by 

 more deliberate control of kidney activity, e.g. by dilatation of kidney blood vessels. 

 It is plain that an aquatic animal has ample opportunity for passing water through the 



