melted alfo; and this was repeated feveral times, till we grew tired, and at laft left them covered up in the yard, to freeze by the joint operation of the furrounding mix ture and the natural cold of the atmosphere. They were frozen at laft after having exhaufted the whole powers of life in the production of heat. That this was really the cafe, could not be known, till I had completed that part of the experiment, for which the whole was begun; viz. the thawing of the animals. This was done very gradually; but the animals did not with flexibility recover life. While in this cold, they thewed figns of great uneafinefs by their violent motions. In fome of these experiments, where air was made the conductor of the cold and heat, that the heat might be more readily carried off from the animal, a leaden veffel was ufed. It was fmall for the fame reafon; and as it was neceffary, for the animal's refpiration, that the mouth of the veffel fhould communicate with the open air, it was made pretty deep, that the cold of the atmosphere round the animal might not be diminished faft by the warmth of the open air, which would have fpoiled it as a conductor.

II. The fecond upon a dormoufe. funk in the cold to its edge.

experiment was The veffel was mixture almoft The atmosphere

round the animal foon cooled; its breath froze as it came from the mouth; an hoar-froft gathered on its whiskers, and on all the infide of the veffel; and the external ends of the hair became covered with the fame. While this was going on, the animal fhewed figns of great uneafinefs: fometimes it would coil itself into a round form, to preferve its extremities, and confine its heat, but finding that ineffectual, it then endeavoured to make its efcape; its motions became less violent by the finking of the vital powers; and its feet.were frozen; but we were not able to keep up the cold a fufficient time to freeze the whole animal, its hair being fuch a bad conductor of heat, that the confumption was not more than the animal powers were capable of fupporting t.

III. The third experiment was made upon another dormouse. From the failure of the laft experiment, I took care that the hair should not a fecond time be an ob ftruction to the fuccefs of our experiment. I therefore firft wetted it all over, that the heat of the animal might be more inftantaneously carried off; and then it was put into the leaden veffel. The whole was put into the cold mixture as before. The animal foon gave figns of its feeling the cold, by repeated attempts to make its efcape. The breath, and the evaporating water from its body

were

were foon frozen, and appeared like a hoar-froft on the fides of the veffel, and on its whiskers; but while the vigour of life lafted, it defied the approach of the cold. However, from the hair being wet, and thereby rendered a good conductor of heat, there was à múch greater confumption of it than in the former experiment. This haftened on a diminution of the power of producing it. The animal died, and foon became ftiff; upon thawing it, we found it was dead.

IV. The fourth experiment was upon a toad. It was put into water juft deep enough not to cover its mouth, and the whole was put into the cold mixture, now between io° and 15°. It allowed the water to freeze clofe to it, which as it were closed it in; but the animal did not die, and therefore was not frozen: however, it hardly ever recovered the ufe of its limbs.

V. The fifth experiment was with a fnail, which froze very foon, in a cold between 10° and 130; but this experiment was made in the winter, when the living powers of thofe ani mals are very weak: it might have refifted the cold more ftrongly in the summer.

I. I took a young growing bean, about three inches long in the ftalk, and put it into the leaden veffel with common water, and then immerfed the whole into the cold mixture. The water very foon froze all round it; however, the bean itself took up a longer time in freezing than the fame quantity of water would have done; yet it did freeze, and was afterwards thawed, and planted in the ground, but it foon withered. The fame experiment was made upon the bulbous roots of tulips, and with the fame fuccefs.

II. A young Scotch fir, which had two complete fhoots and a third growing, and which confequently was in its third year, was put into the cold mixture, which was between 15° and 17°. The last fhoot froze with great diffi culty, which appeared to be owing in fome measure to the repulfion between the plant and the water. When thawed, the young fhoot was found flaccid. It was planted; the firft and fecond fhoot we found retained life, while the third, or growing fhoot, withered.

III. A young hoot of growing oats with three leaves, had one of the leaves put into the cold mixture at 22°, and it foon was frozen. The roots were next put in, but did not freeze; and when put into the ground, the whole grew, excepting the leaf which The fame exhad been frozen.

periment was made upon the leaves and roots of a young bean, and attended with the fame fuc cefs.

IV. A leaf taken from a growing bean was put into the cold mixture, and frozen, and afterwards thawed, which ferved as a

ftandard. Another fresh leaf was taken and bent in the middle upon itfelf; a small shallow leaden veffel was put upon the top of the cold mixture, and the two leaves put upon its bottom; but one half of each leaf was not allowed to touch the veffel by the bend; the cold mixture was between 17° and 15°, and the atmosphere at 22. The furfaces of the two leaves which were in contact with the lead were foon frozen in both; but thofe furfaces which rofe at right angles, and were therefore only in contact with the cold atmosphere, did not freeze in equal times; the one that had gone through this procefs before, froze much fooner than the fresh one. The above experiment was repeated when the cold mixture was at 25°, 24, and the atmofphere nearly the fame, and with the fame fuccefs; only the leaves were longer in freezing, efpecially the fresh leaf.

V. The vegetable juices above mentioned being frozen in the leaden veffel, the cold mixture at 28°, and the atmosphere the fame, a growing fir-fhoot was laid upon the furface, alfo a bean leaf; and upon remaining there fome minutes, they were found to have thawed the furface on which they lay. This I thought might arife from the greater warmth of thefe fubftances at the time of application; but by moving the fir-fhoot to another part, we had the fame effect produced.

VI. A fresh leaf of a bean was exactly weighed; it was then put into the cold atmosphere and frozen. In this ftate it was put back into the fame fcale, and allowed to thaw. No alteration in the weight was produced.

It appears from the above experiments, that an animal must be deprived of life before it can be frozen. Secondly, that there is an exertion, or an expence of animal powers, in doing this, in proportion to the neceffity; and that the whole animal life may be exhaufted in this way. Thirdly, that this power is in proportion to the perfection of the animal, the natural heat proper to each fpecies, and to each age. It may alfo perhaps depend, in fome degree, on other circumftances not hitherto obferved: for from experiment II. and III. upon dormice, I found that in thefe animals, which are of a conftitution to retain nearly the fame heat in all temperatures of the air, it required the greatest cold I could produce to overcome this power; while in experiment IV. and V. this power in the toad and fnail, whole natural heat is not always the fame, but is altered very materially according to the external heat or cold, was exhaufted in a degree of cold not exceeding 10 or 15: and the fnail being the most imperfect of the two, its powers of generating heat were by much the weakest.

That the imperfect animals will allow of a confiderable variation in their temperature of heat and cold, is proved by the following experi ments. The thermometer being at 45°, having introduced the ball by the mouth into the ftomach of a frog, which had been expofed to the fame cold, it rofe to 49. I then put the frog into an fphere made warm by heated wa ter, and allowed it to ftay there twenty minutes; when, upon introducing the thermometer into the ftomach, it raifed the quick

atmo

filver to 64°. But to what degree the more imperfect animals are capable of being rendered hotter and colder, at one time than another, I have not been able to determine. The torpidity of thefe animals in our winter is probably owing to the great change wrought in their temperature by the external heat and cold. The cold in their bodies is carried to fuch a degree, as in great meafare to put a ftop, while it lafts, to the vital functions. In warmer climates no fuch effect is produced. In this refpect they refemble vegetables.

From the foregoing experiments it appears; firit, that plants when in a ftate of actual vegetation, or even in fuch a flate as to be capable of vegetating under certain circumftances, must be deprived of their principle of 'vegetation before they can be frozen. Secondly, vegetables have a power within themfelves of producing or generating heat; but not always in proportion to the diminution of heat by application of cold, fo as to retain at all times an uniform degree of heat; for the internal temperature of vegetables is fufceptible of variations to a much greater extent indeed than that of the more imperfect animals; but fill within certain limits. Beyond thefe limits the principle of vegetable, as of animal life, refifts any further change. Thirdly, the heat of vegetables varies, according to the temperature of the medium in which they are, which we difcover by varying that temperature, and obferving the heat of the vegetable. Fourthly, the expence of the vegetating powers in this cafe is proportioned to the neceffity,

and the whole vegetable powers may be exhaufted in this way. Fifthly, this power is most probably in proportion to the perfection of the plant, the natural heat proper to each fpecies, and the age of each individual. It may alfo perhaps depend, in fome degrce, on other circumflances not hitherto obferved; for in experiment II. the old fhoot did not lofe its powers, while that which was young or growing did; and in experiment III. and IV. we found that the young growing shoot of the fir was with great difficulty frozen at 10°, while a bean-leaf was cafily frozen at 22°; and in experiment V. the young shoot of the fir thawed the ice at 28°, much fafter than the leaf of the bean. Sixthly, it is probably by means of this principle, that vegetables are adapted to different climates. Seventhly, that fufpenfion of the functions of vegetable life, which takes place during the winter feafon, is probably owing to their being fufceptible of fuch a great variation of internal temperature. Eighthly, the roots of vegetables are capable of refifting cold more than the ftem or leaf; therefore, though the ftem be killed by cold, the root may be preferved, as daily experience evinces. The texture of vegetables alters very much by the lofs of life, especially thofe which are watry and young: from being brittle and crifp, they become tough and flexible. The leaf of a bean when in full health is thick and maffy, repels water as if greafy, and will often break before it is confiderably bent; but if it is killed flowly by cold, it will lofe all thefe properties, becoming then pliable and flaccid; deprived

of

of its power of repelling water, it is eafily made wet and appears like boiled greens. If killed quickly, by being frozen immediately, it will remain in the fame state as when alive; but upon thawing, will immediately lofe all its former texture. This is fo remarkable, that it would induce one to believe, that it loft confiderably of its fubitance: but from experiment VI. it is evident that it does not. The fame thing happens to a plant when killed by electricity. If a growing juicy plant receives a ftroke of electricity fufficient to kill it, its leaves droop, and the whole becomes flexible.

So far animal and vegetable life appear to be the fame; yet an animal and a vegetable differ in one very material circumftance, which it may be proper to take particular notice of in this place, as it fhews itself with remarkable evidence in thefe experiments. An animal is An animal is equally old in all its parts, excepting where new parts are formed in confequence of difcafes; and we find, that thefe new or young parts in animals, like the young hoots of vegetables, are not able to fupport life equally with the old; but every plant has in it a feries of ages. According to its years, it has parts of all the fucceffive ages from its first forma tion; each part having powers equal to its age, and each pait, in this refpect, being fimilar to animals of fo many different ages. Youth in all cafes is a flate of imperfection; for we find that few animals that come into the world

in winter live, unless they are par. ticularly taken care of; and we may obferve the fame of vegeta bles. I found that a young plant was more easily killed than an old one; as alfo the youngest part of the fame plant.

This power of generating heat feems to be peculiar to animals and vegetables while alive. It is in both a power only of oppofition and refillance; for it is not found to exert itself spontaneously and unprovoked; but must always be excited by the energy of fome external frigorific agent. In animals it does not depend on the motion of the blood, as fome have fuppofed, because it belongs to animals who have no circulation; befides, the nose of a dog, which is nearly always of the fame heat in all temperatures of the air, is well fupplied with blood: nor can it be faid to depend upon the nervous fyftem, for it is found in animals that have neither brain nor nerves. It is then most probable, that it depends on fome other prin ciple peculiar to both, and which is one of the properties of life; which can, and does, act independently of circulation, fenfation, and volition; viz. that power which preferves and regulates the internal machine, and which appears to be common to animals and vegetables. This principle is in the most perfect state when the body is in health, and in many deviations from that ftate, we find that its action is extremely uncertain and irregular; fometimes rifing higher than the ftandard, and at

other