Mechanisms that determine functional residual capacity in different mammalian species

humans, a value in excellent agreement with the Theory of Homomorphism (Heusner and Tracy, unpublished observations). Ruminants are physiologically very different, i.e., their higher respiratory frequencies may be related to C0 2 production in their rumen (5). Because the content of the reticulum and rumen represents 10 to 15% of body mass (6), these animals are also very different with respect to body composition. A recent statistical analysis (Heusner and Tracy, unpublished observations) shows no significant deviation from homomorphism for tidal volume (b = 1.10 ± 0.08; n = 34; bth = 1) and minute volume (b = 0.86 ±