animal heat. The power which living bodies possess of maintaining the same degree of heat under every change of sur rounding temperature, is one of their most surprising phenomena, and one which occupies a very prominent station in that complicated assemblage of circum stances denoted by the term life. The temperature of the blood, and of the in• ternal parts of the body in general, is stated at about 98° Fahrenheit. In Mr. Hunter's experiment, he found the heat under the tongue, and at the bulb of the urethra, to be 97° ; in the rectum ; in the rectum of an ox and rabbit 994° ; of a lren 103 ; in the heart, liver, and stomach of animals 100° and 101°. 'nese tempe ratures, instead of varying like those of inanimate bodies, according to the sur rounding media, and consequently tend ing to a state of equilibrium, are maintain ed with very little deviation under very great varieties of atmospheric heat. Pal las sustained a cold of 80° below 0 in Si beria, and Gmelin of 126° in the same country. On the contrary, temperatures of 120° and more above 0 have been ob served in Africa and America. Linings saw the thermometer at 126° in Carolina; but when placed under the tongue, or in the axilla, it sunk to the point of animal beat. Much higher degrees of artificial temperature have been supported by the human body. Girls in France staid in an oven where fruit and meal were baking for ten minutes, without inconvenience, the thermometer at 265°. Dr. Fordyce and Sir Joseph Banks supported nearly au equal degree of artificial heat in this country.
From these facts, it is obvious that, al: though in rare instances, the surrounding heat is greater than that of our own bo dies, it is generally considerably less: Hence we must explain the powers by which our temperature is maintained so much above that of the medium in which we live. This explanation is now gene rally founded on the chemical changes which the blood undergoes in the lungs, and in its circulation through the body, which subject is considered under the ar ticle HEAT. There are many circum stances in favour of this explanation ; as the increased heat produced by the acce leration of the circulation by exercise, &c. the coldness of a limb, when the nutrient artery is tied ; the various degrees of tem perature in different animals correspond ing with the perfection of their pulmonary system, &c. There are also several facts which show, that the living powers of the i constitution, or part, greatly influence the evolution of heat, independently of the consumption of oxygen in respiration. The coldness of palsied limbs, the increased heat of parts in inflammation, and of the whole skin in febrile complaints, are suffi cient to prove this. But it is most clear ly demonstrated by an experiment of Dr. Currie's. lie placed a man in a cold bath of which at first diminished his tem perature, but it soon regained the natural standard. Here there must have been a great evolution of heat to keep up the temperature under circumstances so strongly tending. to depress it ; yet the
consumption of oxygen was less than usual, for both the pulse and respiration becaine slower. Mr. Hunter made many experiments on this subject, and conclud ed, that there is always an exertion or expense of atrimal power in resisting cold proportioned to the necessity of the case ; that this'exertion is in proportion to the perfection of the animal, and to the de gree of heat natural to the species and that it is independent of circulation, voli tion, and sensation.
The power of resisting heat arises from the evaporation that is constantly going on from the surface of the skin, and which becomes extremely abundant when the temperature of the air is much raised. See the account of the organ of touching. This is a very powerful means of dimi nishing animal temperature, and conse quently, when long continued, has a very weakening effect. Of fourteen persons shipwrecked in December, three sat on the deck, out of water, but exposed to sleet, snow, and wind ; the evaporation Yrom their surface must have been im mense, and they died. All the others were.up to the middle or shoulders in AL. the water for twenty-three hours, yet survived.
:.Animal heat may be altered from its standard by external applications or dis ease; but the change can be carried much further below the standard than above it. A man could bear to have his penis cooled to 50°; but it could not be heated beyond 100°; although the heat employed raised a dead penis to 114°.
Secretion. The blood, circulated in the manner we have just mentioned, and pre pared by the organs of respiration, is the source from which the various fluids of the animal body are formed in the pro cess of secretion.
The various arrangements of these pro ducts are, in a great measure, arbitrary. Milk seems to be formed by the most easy process, as it resembles so strongly the nature of chyle. Next come the wa tery fluids ; (so called from their appear ance, although in composition they differ considerably from water, chiefly in con taining albumen). The humours of the eye, the tears, sweat, lymph of the cellu lar substance, vapour of the thorax, ab domen, and pericardium, and the water of the ventricles, belongto this class. The urine seems to come under the same head, although it is of a peculiar and com pound nature ; next follow the salivary and pancreatic juices ; and then the mu cous fluids poured into the alimentary, fat, marrow, grease of the Skin, sebaceous matter of the eye-lids, and of the external organs of generation in both sexes, constitute the class of adipous flu ids. The liquor of the amnion, the syno via of the joints, and the prostatic are of a gelatinous kind. '17 he male semen, and the bile, are both of a very peculiar nature. The chemical analysis of these fluids will be considered under their pro per articles.