disagreeable; but, in a few minutes, all uneasiness was removed by copious perspiration. At the end of twelve minutes he left the room very much fatigued, but not otherwise disordered. The thermometer had risen to 220°. In other experiments, it was found, that a heat of even 260° could be borne with tolerable ease. At this temperature, every piece of metal was intolerably hot; small quantities of water, in metallic vessels, quickly boiled; and streams of moisture poured down over the whole surface of the body. That this was merely the vapour of the room, condensed by the cooler skin, was proved by the fact, that when a Florence flask, filled with water of the same temperature as the body, was placed in the room, the vapour condensed in like manner upon its surface, and ran down in streams. Whenever they breathed upon the thermometer the mercury sank several degrees. Every expiration, especially if made with any degree of violence, communicated a pleasant impression of coolness to the nostrils, scorched immediately before by the hot air rushing against them when they inspired. In the same manner, their comparatively cool breath cooled their fingers, whenever it reached them. "To prove," says Sir Charles Blagden, "that there was no fallacy in the degree of heat, shown by the thermometer, but that the air, which we breathed, was capable of producing all the well-known effects of such an heat on inanimate matter, we put some eggs and a beefsteak upon a tin frame, placed near the standard thermometer, and farther distant from the cockle than from the wall of the room. In about twenty minutes, the eggs were taken out, roasted quite hard; and in forty-seven minutes the steak was not only dressed, but almost dry. Another beef-steak was rather over done in thirtythree minutes. In the evening, when the heat was still greater, we laid a third beef-steak in the same place; and as it had now been observed, that the effect of the heated air was much increased by putting it in motion, we blew upon the steak with a pair of bellows, which produced a visible change on its surface and seemed to hasten the dressing; the greatest part of it was found pretty well done in thirteen minutes."

In all these experiments, and similar ones were made in the following year by Dobson of Liverpool, the heat of the body, in a high temperature, speedily reached 100°, but exposure to 212° and more did not carry it higher. These results are not, however, exactly in accordance with those of MM. Berger and De La Roche, deduced from experiments, performed in 1806. Having exposed themselves for some time to a stove,—the temperature of which was 39°. of Reaumur, or 120° of Fahrenheit,—their temperature was elevated 3° of Reaumur, or 63° of Fahrenheit; and M. De La Roche found, that his rose 4° of Reaumur, or 9° of Fahrenheit, when he had remained sixteen minutes in a stove, heated to 176° of Fahrenheit. In some experiments of Chabert, who has been exhibiting his powers as a "Fire-king," in this country as

well as in Europe, he is said to have entered an oven with impunity, the heat of which was from 400 to 600° of Fahrenheit.

Experiments have shown, that the same power of resisting excessive heat is possessed by other animals. Drs. Fordyce and Blagden shut up a dog in a room, the temperature of which was between 220° and 236° for half an hour; at the end of this time, a thermometer was applied between the thigh and flank of the animal; and in about a minute, the mercury sank down to 110°; but the real heat of the body was certainly less than this, as the ball of the thermometer could not be kept a sufficient time in proper contact, and the hair, which felt sensibly hotter than the bare skin, could not be prevented from touching the instrument. The temperature of this animal, in the natural state, was 101°.

We find, in the case of aquatic animals, some astonishing cases of adaptation of beings to the medium in which they live. Although man is capable of breathing air, heated to above the boiling point of water with impunity, we have seen that he cannot bear the contact of water much below that temperature. Yet we find fishes living in water at a temperature, which would be entirely sufficient to boil them if dead. In the thermal springs of Bahia, in Brazil, many small fishes are seen swimming in a rivulet, that raises the thermometer to 88°, when the temperature of the air is only 774. SONNERAT, again, found fishes existing in a hot spring at the Manillas, at 158° Fah.; and MM. Humboldt and Bonpland, in travelling through the province of Quito in South America, perceived fishes thrown up alive and apparently in health, from the bottom of a volcano, in the course of its explosions, along with water and heated vapour that raised the thermometer to 210°, or only two degrees short of the boiling point.

When the heating influence is applied to a part of the body only, as to the urethra, the temperature of the part is not increased beyond the degree to which the whole body may be raised.

From all these facts, then, we may conclude, that when the body is exposed to a temperature, greatly above the ordinary standard of the animal, a frigorific influence is exerted; but this is effected at a considerable expense of the vital energy; and hence is followed by considerable exhaustion, if the effort be prolonged.

In the cold-blooded animal, the power of resisting heat is not great; so that it expires in water not hotter than the human blood occasionally is. Dr. Edwards found, that a frog, which can live for eight hours in water at 32°, is destroyed in a few seconds, in water at 105°; which appears to be the highest temperature, that cold-blooded animals can bear.

Observation has shown, that although the average temperature of an animal is such as we have stated in the table, yet that particular circumstances give occasion to some fluctuation. A slight difference exists, according to sex, temperament, idiosyncrasy, &c. MM. Edwards and Gentil found the temperature of a young

female half a degree less than that of two boys of the same age. Edwards tried the temperature of twenty sexagenarians, thirtyseven septuagenarians, fifteen octogenarians, and five centenarians, at the large establishment of Bicêtre, and he observed a slight difference in each class. John Davy found, that the temperature of a lamb was a degree higher than that of its mother; in five newborn children, the heat was about half a degree higher than that of the mother, and it rose half a degree higher in the first twelve hours after birth. Edwards, on the other hand, found, that, in the cold-blooded animal, the faculty of producing heat was less, the nearer to birth; and that in many cases, as soon as the young dropped from the mother, the temperature fell to within a degree or two of that of the circumambient air; and he moreover affirms, that the faculty of producing heat is at its minimum at birth; and that it increases successively to the adult age. His trials on children, at the large Hopital des Enfans of Paris; and on the aged, at Bicêtre, showed, that the temperature of infants, one or two days old, was 94° or 95° of Fahrenheit; that of the sexagenarian from 95° to 97°; of the octogenarian 94° or 95°; and that, as a general principle, it varied according to the age.

The state of the system, as to health or disease, also influences the evolution of heat. Dr. Francis Home, of Edinburgh, took the heat of various patients, at different periods of their indispositions. He found that of two persons, labouring under the cold stage of an intermittent, to be 104°; whilst, during the sweat and afterwards, it fell to 101° and to 99°. The highest degree, which he noticed in fever, was 107°. We have often witnessed the thermometer at 106° in scarlatina and in typhus, but it probably rarely exceeds this, although it is stated to have been seen as high as 112°.

Hunter found the interior of a hydrocele, on the day of operation, to raise the mercury to 92°; on the following day, when inflammation had commenced, it rose to 99°. The fluid, obtained from the abdomen of an individual, tapped for the seventh time for dropsy of the lower belly, indicated a temperature of 101°. Twelve days thereafter, when the operation was repeated for the eighth time, the temperature was 104°.

Dr. James Currie had himself bled; and during the operation, the mercury of a thermometer, which he held in his hand, sank, at first slowly and afterwards rapidly, nearly 10°; and when he fainted, the assistant found, that it had sank 8° farther.

MM. Edwards and Gentil also assert, that they have observed diurnal variations in the temperature of individuals, and these produced, apparently, by the particular succession in the exercise of the different organs; as where intellectual meditation was followed by digestion. These variations, they affirm, frequently amounted to two or three degrees, between morning and evening.

Such are the prominent facts, connected with the subject of ani

mal heat. It is obvious, that it is altogether disengaged by an action of the system, which enables it to counteract, within certain limits, the extremes of atmospheric heat and cold. The animal body, like all other substances, is subjected to the laws regarding the equilibrium, the conduction, and the radiation of caloric; but, by virtue of the important function we are now considering, its own temperature is neither elevated nor depressed by those influences to any great amount. Into the seat and nature of this mysterious process, and the various ingenious theories, that have been indulged, we will now inquire.

Physiologists have been by no means agreed, regarding the organs or apparatus of calorification. Some, indeed, have affirmed that there is not, strictly speaking, any such apparatus; and that animal heat results from all the other vital operations. Amongst those, too, who admit the existence of such an apparatus, a difference of sentiment prevails; some esteeming, that it is local, or effected in some particular part of the body; others, that it is general, or disseminated through the whole of the economy.

Under the name caloricité Chaussier admits a primary vital property, by virtue of which living beings disengage the caloric on which their proper temperature is dependent, in the same manner as they accomplish their other vital operations, by other vital properties; and, in support of this doctrine, he adduces the circumstance, that each living body has its own proper temperature; which is coexistent only with the living state; is common to every living part; ceases at death; and augments by every cause, that excites the vital activity.

It has been properly, however, objected to this view, that the same arguments would apply equally to many other vital operations; to nutrition for example; and that it would be obviously improper to admit, for each of these functions, a special vital principle. The notion has not experienced favour from the physiologist, and is, we believe, confined to the individual from whom it emanated.

Boni, again, according to Adelon, considers that no particular organ is specially charged with the disengagement of caloric; but that it is the common resultant of all the vital actions, nervous or muscular, of digestion, respiration, circulation, nutrition, secretion, &c. The arguments, that he adduces, in favour of his position, are,—that the exercise of any of these functions actually modifies the temperature of the body; that mental labour heats the head,—hence the excitement witnessed in the maniac, and the great resistance to cold for which he is distinguished; and that, during emotion, we are hot or cold, whatever may be the condition of the atmosphere.

The action of the various organs of the body, and especially of the nervous system, we shall see, have considerable influence in modifying the disengagement of heat; and it is probable, that it

occurs in the different organs, referred to by Boni, but not directly in consequence of the functions they accomplish.

Amongst those, who admit that calorification is a local action, some have believed that the caloric is disengaged in a particular organ, whence it is distributed to every part of the body; whilst others conceive, that every part disengages its own caloric and has its special temperature.

So striking a phenomenon as animal temperature could not fail to attract early attention; and, accordingly, we find, amongst the ancients, various speculations on the subject. The most prevalent was, that its seat is in the heart; that it is communicated to the blood in that viscus, and is afterwards sent to every part of the system; and that the great use of respiration is to cool the heart; but this hypothesis is liable to all the objections, that apply to the notion of any organ of the body acting as a furnace,—that such organ ought to be calcined; and it has the additional objection, which applies to all the speculations regarding the ebullition and effervescence of the blood as a cause of heat, that it is purely conjectural, without the slightest fact or argument in its favour. It was not, indeed, until the chymical doctrines prevailed, that any thing like argument was adduced in favour of the local disengagement of heat: the opinions of physiologists then settled almost universally upon the lungs ; and this chiefly in consequence of the observation, that animals, which do not breathe, have a temperature but little superior to the medium in which they live; whilst man and animals that breathe have a temperature considerably higher than the medium heat of the climate in which they exist, and one which is but little affected by changes in the thermal condition of that medium; and, moreover, that birds, which breathe, in proportion, a greater quantity of air than man, have a still higher temperature than he.

Mayow, whose theory of animal heat was, in other respects, sufficiently unmeaning, affirmed, that the effect of respiration is not to cool the blood, as had been previously maintained, but to generate heat, which it did by an operation analogous to combustion.

It was not, however, until the publication of Dr. Black's doctrine on latent heat, that any plausible explanation of the phenomenon appeared. According to that distinguished philosopher, a part of the latent heat of the inspired air becomes sensible; consequently, the temperature of the lungs and of the blood passing through them must be elevated; and as the blood is distributed to the whole system, it communicates its heat to the parts as it proceeds in its course. But this view was liable to an obvious objection, which was, indeed, fatal to it, and so Black himself appears to have thought, from his silence on the subject. If the whole of the caloric is disengaged in the lungs, as in a furnace, and is distributed through the blood-vessels, as heated air is trans