Man’s state and condition, at his birth, place him in very different circumstances from those at which he subsequently arrives. Here, therefore, we see an extensive field of inquiry; and it is suggested whether, in the infantile state, man generates _less heat_ than in more matured existence. Dr. Edwards has shown that the young of mammiferæ generally, being born at the period when their eyes are open, produce _less_ heat than adults. It is, therefore, presumable that the generating powers of heat differ in the two states of existence which man goes through, the infantile and mature. But the power of producing heat differs among adult animals, and it is desirable to know the limits of this faculty, [p304] Moreover, this power differs in different parts of the body; so that, when experiments are made, we should always apply the thermometer to the same part of the body. Among twenty adult persons, Dr. Edwards found the average temperature 36°.12: in infants from a few hours to two days old, 34°.75 was the average. Thus we perceive that the temperature of human infants is _inferior_ to that of adults. In infants born previous to the usual period, two or three hours after birth their heat was at 32° of Reaumur’s scale. So far we perceive a similarity in man to the mammiferæ in general. We have next a chapter on the effects of _cold_ upon mortality at different ages. It is highly interesting to observe the care of animals towards their offspring, in protecting them against the effects of cold instinctively at a period before their own powers of generating heat enable them to resist its baneful tendency. Dr. Edwards endeavours to investigate the subject of cold, so as to discover its limit of action. He examined the young of mammiferæ and birds, the former born with closed eyes, and the latter unfledged. He exposed them separately and apart to the air, so as to be independent of each other’s warmth, and they exhibited a temperature below their natural standard at the period of birth, even when a degree of artificial heat was applied beyond that of adult birds. The final result of these experiments was, that the application of heat may be conducive to their developement, but is not indispensable to their preservation. The author discovered, that the diminution of temperature is not equally injurious at all ages. The _younger_ the animal, the _less_ is the injury sustained by cold, because the faculty of producing heat is less powerful with the young than with the matured animal, the power increasing as the animal grows, and also with the increase of cold.