IN THE ANIMAL KINGDOM. 27 



but that the C0 2 -capacity is not affected by differences in the tensions of 0; 

 and that the absorptive capacities of hemoglobin for O and C0 2 are 

 higher in the hemoglobin of the dog and guinea-pig than in that of the 

 goose. The large C0 2 -capacity of hemoglobin is suggestive of phys- 

 iological importance, yet it seems to be almost entirely ignored by the 

 physiologist. 



Bohr, Hasselbalch, and Krogh made the important biological obser- 

 vation that a positive relationship exists between the percentage of in the 

 blood in the presence of different tensions of C0 2 . They made a large 

 number of experiments in which the tension of O varied from 5 to 150 mm. 

 of Hg, and in which the tension of C0 2 was 5, 10, 20, 40, and 80 mm. of 

 Hg, the absorption being determined in fresh dog's blood at 38. They 

 found that when the tension is high (corresponding to the pressure in the 

 pulmonary alveoli) differences in the tension of C0 2 are without important 

 influence on the quantity of absorbed ; but when the tension of is low (as 

 in the blood of the capillaries of the tissues generally) an increase in the 

 tension of C0 2 has a very depressing effect on the absorption of O. Assuming 

 the tension of in venous blood to be 25 mm. of Hg and that CO 2 is absent or 

 without influence, only about 24 per cent of the O of the hemoglobin would be 

 given off, but if the tension of C0 2 were 40 and 80 mm. of Hg, as much as 

 60 and 78 per cent, respectively, would be given off without the tension of the 

 O falling below 25 mm. of Hg. It seems from this that the high tension of 

 the CO 2 in the tissues must have an important influence on the rapid dis- 

 sociation of O from the oxyhemoglobin. 



THE NON-IDENTITY OF HEMOCYANINS. 



Krukenberg (page 9) has found that hemocyanins from different 

 sources show differences in their behavior towards and CO 2 ; Howell 

 (page 10) noted difference in hemocyanins as regards the condition of the 

 respiratory and the temperature of coagulability; Cuenot (page 12) 

 refers to a hemocyanin which is colorless, which does not become blue upon 

 exposure to the air, and which he regards as being not respiratory; and 

 Couvreur (page 13) noted differences in the degree of stability. 



THE IDENTITY OR NON-IDENTITY OF CORRESPONDING 

 RESPIRATORY SUBSTANCES. 



As regards the identity or non-identity of corresponding respiratory 

 substances, it seems probable, from the literature on the subject: (1) that 

 chlorophyl (pigment), like hematin, is an identical substance from whatever 

 source; (2) that there are several forms of achroglobulin ; (3) that hemocyanin 

 is not a uniform substance, and that the same conclusion applies to hemo- 

 globin, echinochrome, and chlorocruorin. 



