Abstract
Partial pressures of oxygen and CO 2, in subcutaneous gas pockets were measured in three small wild mammals, short tailed shrew (Blarina brevicauda), pocket mouse (Perognathus penicillatus), and little brown bat (Myotis lucifugus). In the bat, day and night time samples were taken. The group mean O 2 and CO 2 values (+-S.D.) were, in each species, as follows: Shrew, P O 2 = 37±6, P CO 2 = 53 +-5; pocket mouse, P O 2 = 44±11, P CO 2 , = 38.5±7; bat, day time P O 2 =40±7, P CO 2 = 33.8 night time P O 2 , = 45±7, P CO 2 , = 38+-4. The P O 2 , is within the range normally measured in larger mammals, and it is concluded that mean “tissue” oxygen tension may therefore be an interspecific constant. If the subcutaneous pocket P O 2 is at all indicative of Pv̄o 2, then Pao 2 —Pv̄o 2 is also an interspecific constant, but because the oxyhemoglobin dissociation curve shifts down and to the right in small animals, Cao 2—Cv̄o 2, cannot also be a constant, as ∝ o 2, would require, hence, the relationship ∝ M 0.74 cannot be true. The pocket P CO 2 values show greater interspecific difference but are still within the range seen in larger mammals. More knowledge concerning species differences in blood CO 2 absorption curves is required to interpret the CO 2 data.
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