contrary, that he was not able to observe any relation between the temperature of the air, and the degree of its deoxidation.

In his second paper, he more minutely attended to the temperature of different kinds of animals when exposed to great degrees of heat; he found it to be not so stationary as had been generally supposed, being frequently raised by 10° or 13° above the natural standard, although it still remains very much below the temperature in which an animal can live for a certain length of time without any considerable uneasiness. With respect to cold-blooded animals, although their heat is much less stationary than those with warm blood, he found that in high temperatures it fell considerably below that of the medium; frogs, for example, in air heated from 110° to 115°, were no more than 80° or 82°. He entered upon a second set of experiments for the purpose of directly ascertaining the effect of evaporation upon the temperature of animals, the results of which fully confirmed his former opinion, pointing out an obvious relation between the amount of evaporation and the degree in which the animals were able to resist great heats. One set of experiments consisted in enclosing various animals, for example, rabbits, guinea-pigs, and pigeons, in a box which was filled with steam; it was found that when the temperature of the apparatus was equal to, or greater than that of the body, the temperature of the animal was raised, and the inconvenience which it suffered was proportionally great.

In his third paper, Dr. Delaroche more particularly directs his attention to the chemical effects of respiration upon the air under different circumstances. Having proved in the former paper that when the evaporation from the skin and lungs is prevented, the cooling process is suspended, it was an interesting subject of inquiry whether, in this case, the chemical effects of respiration continue with as much activity as under ordinary circumstances. The experiments which were performed for the purpose of ascertaining this point, seem to have been sufficiently numerous and well conducted, and the result was, that the consumption of oxygen is greater as the temperature is lower, upon the average, about as 6 to 5. The formation of carbonic acid does not, however, follow the same ratio with the consumption of oxygen, being not only in all cases less, so as to indicate an absorption of oxygen, but it was found that this excess, or the difference between the oxygen consumed and the carbonic acid produced, was less at a high than at a low temperature, amounting upon the average to no more than one-tenth, or not more than half of the difference of the consumption of oxygen at different temperatures. The opinion of Crawford, Jurine, and Lavoisier, appears therefore, to a certain extent, to be thus confirmed, but Dr. Delaroche supposes that the effects observed in these experiments were not sufficient to explain the equalization of the temperature, without the aid of the cooling process of evaporation, and indeed this had been so fully established in the former experiments as to leave no doubt of its agency.

Our general conclusion will therefore be, that at high temperatures there is less caloric actually evolved, but that the circumstance which principally contributes to equalize the heat is the cutaneous and pulmonary evaporation, while at temperatures above that which is natural to the animal, the cooling process must be entirely ascribed to this operation."

But, although we are very much indebted to Dr. Delaroche, there are still some points that require farther investigation. It is proved that evaporation abstracts heat from the body, but it still remains somewhat doubtful, whether the effect thus produced be adequate to the demands of the system, or whe

6 Black very explicitly states his opinion that the heat which is necessarily absorbed in spontaneous evaporation, contributes to enable the body to bear the warmth of tropical climates. He particularly adverts to Fordyce's experiments, and states his opinion that it was owing to the evaporation from the surface that he was able to endure so high a temperature; Lectures by Robinson, v. i. p. 214. Lavoisier, in the course of his researches into the nature of respiration and animal heat, frequently refers to the mode by which it is equalized, when the body is exposed to different temperatures. He particularly notices this subject in his paper on transpiration, published in the Mem. Acad. for 1790; he defines this function to consist in "a loss of moisture, which requires heat to dissolve it in the air, and which by the cold thus produced, prevents the temperature from rising above the degree natural to the animal." This opinion was generally adopted by his contemporaries, but it could scarcely be regarded as more than a probable conjecture before the experiments of Delaroche. See Gregory's Conspectus, § 578; the Observations on Animal Heat, from $ 571 to § 580, contain a succinct and elegant epitome of the doctrines which were the most approved .when the work was published..

ther there may not be some other means employed which may co-operate to the same end. It would be desirable to examine with more minuteness than has hitherto been done into the quantity of vapour formed by the body as compared with the cooling effect produced. We should ascertain what temperature would be acquired by an inanimate mass of matter of the same bulk and capacity for heat with the animal body, and compare this with the actual temperature gained, and this again with the quantity of vapour generated. It would also be desirable to ascertain with more minuteness what is the exact effect of the respiratory organs of animals at a temperature higher than what is natural to them, first when the process of evaporation is suffered to proceed, and afterwards when it is suspended; is there any oxygen consumed under these circumstances, or to what amount, or in what degree, does the quantity differ in the two cases? The supposed power of the animal system in producing cold is one that has been treated of in a singularly mysterious manner, and much vague and indeter minate speculation has been employed upon a subject with which the framers of the hypothesis appear to have been very inadequately acquainted. The information which we derive from the experiments of Dr. Delaroche, although not in every respect complete, is, however, of great value; and it enables us to trace out a connexion between the different functions of the lungs, so as to afford, perhaps, the most interesting example which occurs in the animal œconomy, of that beautiful adjustment of the functions

to each other, upon which I have had occasion to remark in other parts of my work; for it appears that not only have the lungs the power of evolving heat in greater or less quantity in proportion to the demands of the system, but that the same organs, under other circumstances, can produce the directly contrary effects, and actually generate cold.

The researches of Dr. Edwards afford us some valuable information on the property which the system possesses of equalizing its temperature under different circumstances. He found that warm-blooded animals have less power of producing heat, after they have been for some time exposed to an elevated temperature, as is the case in summer, while the opposite effect is produced in winter. A series of comparative experiments were performed, which consisted in exposing birds to the influence of a freezing mixture, first in February, and afterwards in July and August, and observing in what degree they were cooled by remaining in this situation for equal lengths of time; the result was, that the same kind of animal was cooled six or eight times as much in the summer as in the winter months. This principle he supposes to be of great importance in maintaining the regularity of the temperature at the different seasons, even more so than evaporation, the influence of which, in this respect, he conceives has been much exaggerated." It would appear, however, that the sudden application of a high or a low temperature has a different effect upou

7 De l'Influence, &c. par. 3. chap. 3.

Ibid. p. 486, 7.