It seems probable that the chief distinction in the calorimetry of warm-blooded and cold-blooded animals is in insulation (sensitivity to cold being the regulating factor). All warm-blooded animals are air-breathing, and air brings much oxygen and takes away little heat. The center of a cluster of bees in winter may be 40° above that of the air bathing it.
The heat-production in a 100-gram cassiopea at 30° is sufficient to raise its body-temperature 0.14° per hour above that of the sur rounding water, but no such difference in temperature has been observed, because the heat generated is conducted away by the water bringing the oxygen. I found that a fish weighing 1.4 grams used 0.825 c.c. per hour at 30°, which is sufficient to raise its body temperature about 3° per hour, but during this time it was required to breathe 400 c.c. of sea-water, even though it removed half of the oxygen from water saturated with air at this temperature. The water circulating through the gills could remove the heat generated if the body-temperature were 0.01° above that of the water. Since the fish probably removed much less than half the oxygen from the water in one passage through the gills, the body-temperature was probably much less than 0.01° above that of the water. Rogers and Lewis could detect no difference between the body-temperature of fish, salamanders, clams, and earthworms and the water in the thermostat in which they were placed, after they had been in the thermostat long enough for equilibrium. They used a thermocouple, and one division of the gal vanometer scale corresponded to 0.0042°.
It was shown that the metabolism of Cassiopea is proportional to its surface and not to its weight (W), but to WI. This is due to the fact that the metabolism is confined to the living cells and that these con stitute a superficial epithelium, whose thickness is about the same in cassiopeas of the range of sizes studied. We might use these results in an attempt to explain the so-called surface-law of warm-blooded animals. Dreyer, Ray, and Walker have shown that the blood-volume and cross-sections of the aorta and trachea are proportional to WI (or surface). If animals were of the same shape (internally as well as externally), the cross-sections of all organs would be proportional to W', but the blood-volume would be proportional to the weight (W).
If the blood-volume is proportional to W', the whole circulatory system would be nearly proportional to and owing to the close relation between the lungs and the blood the volume of the lungs would be nearly proportional to Wt. The volume of the skin may be propor tional to and the volume of the wall of the alimentary tract nearly so. The nerve, muscle, and glandular tissues are excitable, and hence their metabolism must vary. Variable components may be excluded from basal metabolism by definition, but can not all be eliminated in making measurements. Only the skeleton can be said to have a con stant metabolism proportional to W, and since the red bone-marrow produces blood (erythrocytes) and this is proportional to the surface, the metabolism of some of the bones may be nearly proportional to the surface. Benedict has shown that great variations from the surface law exist, and hence it may be only accidental.
The fact that the excitable tissues metabolize more per unit weight in small animals than in large (i. e., proportional to a smaller power of W than unity) is true, not only for warm-blooded animals, but also for cold-blooded animals, to which the teleological principle of the surface law (in relation to heat regulation) does not apply. It seems possible, however, that the chief conditions necessary for the evolution of temperature-regulation in animals were: (1) air breathing; (2) large body size; (3) sensitivity to low temperatures; (4) variation of activity of excitable tissues with size; and (5) epithelial type of architecture, 4 and 5 being more characteristic of cold-blooded animals.
It is hoped that the fact that metabolism varies with tension may explain the increase in metabolism in certain types of acidosis. Lusk and Richie have shown that certain amino acids have a specific dynamic action and Benedict asserts that it has been demonstrated that there is a distinct increase in the basal metabolism with the aci dosis resulting from the ingestion of a carbohydrate-free diet. It is not assumed that amino acids dissociate enough H ions or neutralize enough base to cause acidosis, and whether there is any relation between the phenomena discussed by Lusk and by Benedict may be open to question, but it seems clear that increased metabolism may accompany acidosis.