Animals, then, of warm blood in a state of asphyxia hold their existence on two principal conditions relative to heat; one regarding the different measures by which some develope their heat, and the other the degree of external temperature. The first is proper to animals naturally, the second fortuitous. Upon the _respiration_ of both young and adult animals the author arrives at a conclusion opposite to that of common opinion, which is founded on the notion of the heat in young animals being higher than that of the matured. Finding, [p302] however, as already noticed, that the parent exceeds the temperature of its offspring after birth, it is naturally concluded that its consumption of air is also greatest. This was experimentally confirmed, and is in unison with other facts. In the first part of this work the vertebratæ of cold blood were also found to consume least air in proportion to their diminution of temperature. Temperature seems to act uniformly with all the vertebratæ, and their consumption of air is in proportion. The _mammiferæ_ have a lower temperature than _birds_, and they consume less air than the latter. Fish and reptiles consume less air than the warm-blooded, and possess a lower temperature. The influence of the _seasons_ upon _respiration_ is considered in the sixth chapter. Many changes occur in the atmosphere during the revolutions of the seasons, varieties in the temperature, and the pressure and density of the air. Dr. Edwards shows that the faculty of producing heat with warm-blooded animals is greater in _winter_ than in _summer_, the constitution of animals being adapted to their individual climates; and in reference to the relation of this faculty to the consumption of air, it is presumable, all other circumstances being alike, that the consumption ought to be increased with the faculty of developing heat, and the experiments justify the presumption.