Some experiments on _lizards_, _snakes_, and _turtles_ conclude the researches among cold-blooded animals. The skins of these, like those of the frogs and salamanders, received vivifying influence from the air, mainly acting, in conjunction with pulmonary respiration, to promote their existence. _Snakes_ and _turtle_, their pulmonary respiration being insulated, from their skins being guarded from atmospheric influence, were found alive; but the _lizards_ died in a few hours, when the vivifying contact of the air was removed from their bodies, and they breathed only by their mouths. Animals naturally defended by _scales_ transpire much less than such as have their skins free. Thus _frogs_, _toads_, and _salamanders_ yielded more by perspiration than _lizards_, _snakes_, and _turtle_, in a given time; and the porosity of the skin of course regulates the facility of transpiration in all cases. With these experiments and remarks, Dr. Edwards concludes the second part of his researches. The third part includes _animals of warm blood_, in which will be found some curious and interesting remarks on the heat of young animals compared with that of adults. Dr. Edwards refutes the common notion of young animals being necessarily hotter than adults. The heat of young puppies was very near that of the parent, or one or two degrees less, but this variation was not constant. Some new-born kittens and rabbits were also subjected to similar trials, and the results led to a conclusion that the temperature of young animals is _less_ than that of adults. According to these experiments, the power of resisting the cooling influence of the air acquires force as the animal grows up; and those examples related, in which artificial covering was adopted, show that nudity is not the only cause of the reduction of heat, which is, in fact, more referrible [p299] to their infantile constitution. At first the sucking animal shows little variation from the parent temperature; then this becomes more and more reduced, and about the fifteenth day it is a degree or two below the mother. Birds, which are warmer than mammiferæ, were next made the objects of experimental inquiry, and the young recently hatched exhibited a _lower_ temperature than the grown birds. After removal from the shelter of their nests into a mild atmosphere of 17°, in one hour they cooled down from 36° to 19°, thus losing 17° in an hour. At an elevation of 22° the same results were obtained, and they cooled down to within one degree of the surrounding air. The plumage of birds has little if any influence upon their temperature. The production of heat lies within, and not on the surface of the animal; and if it be strongly developed, the removal of natural coverings does not influence the heat produced; and if it be weak, their addition will not prevent cooling. Birds recently escaped from the shell cooled to within two degrees of the air, whereas the unplumed adult birds scarcely lost one degree.