principle. The only circumstance to which he refers is the increased temperature of the blood drawn from a part suffering under local inflammation, which, as he says, is considerably above that of the blood in the left side of the heart; but the fact is stated generally without any reference. Dumas remarks upon the correspondences between the capacity and structure of the lungs and the temperature of the animal, and hence draws an inference in favour of the chemical theory. He, however, considers it an objection to this doctrine, that the temperature of the animal remains the same, whatever be that of the surrounding medium; he also thinks that the quantity of oxygen consumed in respiration is not sufficient to serve for the support of the temperature, and for the removal of the vapour and carbonic acid; but his objections are brought forward in a general manner, without reference to any particular facts. Legallois, at the conclusion of the experiments, of which an abstract is given above, p. 271, although he supposes that the nerves have an indirect effect upon the evolution of animal heat, states his opinion to be, that when the blood is arterialized its capacity is increased, and that when it is venalized in the capillaries its capacity is changed, and its heat given out; and adds that when, from any cause, the respiration is rendered laborious, by the proper quantity of oxygen not being admitted to the lungs, the temperature is proportionally reduced.*

2

Physiol. t. ii. p. 400.

3 Physiol. t. iii. p. 115. 121,, 171. Ann. de Chim. et Phys. t. iv. p. 118. et seq.

"8

Seguin brings forward various considerations in favour of the connexion between animal heat and the chemical change which the blood experiences in respiration; and Sommering supports the chemical doctrine of animal heat." Cuvier supposes that respiration causes the combination of oxygen with carbon and hydrogen, in consequence of which heat is disengaged. He says, "Le poumon est le foyer de la chaleur animale, et c'est là que le sang puisse celle qu'il porte dans le reste du corps." This chemical doctrine of animal heat, in its essential parts, is also adopted by Blumenbach, although he introduces some modifications into Crawford's theory; he supposes that the blood leaves the lungs charged with latent heat, in consequence of the oxygen which it contains; that it acquires carbon in the small vessels, and sets its latent heat at liberty; and Dr. Elliotson, likewise, although aware of the force of the objections that have been urged against it by Mr. Brodie and others, admits that "many circumstances favour it ;" and appears, upon the whole, disposed to adopt it. I may also remark concerning Dr. Philip's opinion, that although he regards the nervous system as a necessary instrument in the process of calorification, yet we may infer, that he supposes the immediate effect to be produced by the union of oxygen and carbon.2 Sir A. Carlisle remarks upon the correspondence

6 Ann. Chim. t. v. p. 259, 0. 7 Corp. Hum. Fab. t. vi. § 76. Tab. Elem. p. 46. 1 Inst. Phys. p. 101. 4. VOL. II.

in the chap. on Respiration. 9 Inst. Phys. § 167. p. 97, 8. Inq. p. 250. et alibi.

U

between the comparative anatomy of the lungs and the temperature of the animal. Dr. Davy's general conclusion is against Crawford's hypothesis, because he finds no material difference between the capacities of arterial and venous blood, that the temperature of the left side of the heart is higher than that of the right, and that the temperature of the parts of the body generally diminishes as we recede from the heart. These facts, he observes, are more agreeable to Black's hypothesis, although they may be explained on Mr. Brodie's; but upon the whole, he inclines to Black's.*

§ 2. Of the means by which the Animal Temperature is regulated.

Having endeavoured to establish the doctrine that the source of animal heat is in the lungs, and that it depends upon the chemical action of the air on the blood, the next point for our consideration will be the mode by which the uniformity of the animal temperature is preserved. We find that, among the warm-blooded animals, to whatever degree of heat or of cold the body is exposed, the blood and the internal parts always indicate nearly the same degree of heat. According to the view which has been

3 Phil. Trans. for 1805. p. 15.

4 Phil. Trans. for 1814. P. 600..3.

5 The latest observations, and we may presume the most correct, that we possess on this subject, lead us to conclude, that this uniformity is not quite so great as was formerly supposed, especially when we arrive at a temperature nearly equal,

taken above of the cause of animal heat, the question in its strict form will be, by what means is the combination of oxygen and carbon in the lungs so regulated, as that the evolution of heat is in proportion to the demand for it in the system.

But in order to solve this problem, a previous inquiry presents itself; is the combination of oxygen and carbon in the lungs always going forwards at the

This is decidedly

or superior to, that of the body itself. proved by the experiments of Delaroche and Berger, who found that by exposing warm-blooded animals to very high temperatures, they experienced an elevation equal to 7° or 8° (cent.) Journ. Phys. t. lxxi. p. 289. et seq. Dr. Edwards's observations on birds at the different seasons of the year, showed that there was a difference of 4° (cent.) between the winter and summer months; De l'Influence, &c. p. 489. Dr. Davy observed that the temperature of the inhabitants of Ceylon, was 1° or 2° higher than the ordinary standard; ibid. The uniformity of the animal temperature appears to be more steadily maintained in great degrees of cold, where it seems that the heat of the internal parts is scarcely diminished, as long as the functions proceed in their ordinary course. We have many accounts to this effect by travellers and naturalists, but none, perhaps, upon which greater reliance can be placed, than upon that of Capt. Lyon, contained in Capt. Parry's Second Voyage to the Arctic Regions, p. 157. The observations were principally made upon newly killed foxes, the temperature of which was found to be from 106 to 98°, that of the air being from 3° to 32°; it did not appear that there was any relation between the temperature of the air and of the animals. The observations were made at Winter Isle, N. lat. 66° 11', So far as regards the sensations, the experience of these voyagers proved that the state of motion or rest in the atmosphere had a very great effect in exciting the feeling of cold; they found a calm air of 50° more tolerable than a breeze at 0°%.

same rate, and consequently adapted to the lowest tem perature, which is consistent with the continuance of life, or is it found to vary in the inverse proportion to the temperature of the animal? And there is a farther consideration which we must now enter upon; when an animal is placed in a medium, the temperature of which is higher than that natural to itself, we find that the body still remains at nearly its ordinary standard. We have therefore in this case, not merely the suspension of the process by which heat is generated, but it would appear that the contrary effect must be produced, that the body must possess the power of resisting heat, or of actually generating cold. This leads us to the third question which was proposed in the commencement of the chapter; by what means is the body cooled at high temperatures? And as there would appear to be an intimate connexion between this inquiry and the former, it will be more convenient to investigate them in conjunction with each other.

The cases in which the body is exposed to a temperature greater than what is natural to it, are so rare compared to the contrary occurrence, and the effects of such exposure are, in various ways, so unfavourable to the exercise of the vital functions, that it was formerly assumed as an acknowledged matter of fact, that life could not exist under such circumstances. Boerhaave conceived that he had proved this point by direct experiment; but from causes which we cannot now ascertain, there must have been some source of inaccuracy, which interfered with his