VOL. LXV.] PHILOSOPHICAL TRANSACTIONS. 68Q 



Observations. — ^That heated air should have such a speedy and powerful effect 

 in quickening the pulse, while the animal heat is little altered from its natural 

 standard ; that the human body should so easily bear to be surrounded with air 

 heated to 224° ; that the albumen ovi, which begins to coagulate in water at 

 150°, should remain fluid in 224°; and that the same albumen ovi, still placed 

 in air heated to 224°, should coagulate if in contact either with tin or its 

 own shell, are facts as singular as they are difficult of explanation. From the 

 different effects of heated air on the pulse and the heat of the body, do we not 

 discover the fallacy of that theory of animal heat which has been adopted by 

 Boerhaave and other celebrated physiologists ? They suppose that animal heat is 

 produced by the attrition of the globules of the circulating fluids against the 

 sides of the containing vessels ; but in several of the preceding experiments, the 

 circulation was amazingly quickened with little increase of the animal heat. 

 But whence is it that the human body can bear without immediate injury, to be 

 surrounded with air heated to 224° ? And whence is it, that the albumen ovi 

 does not coagulate in this degree of heat ? Is it that fire as it passes into some 

 bodies becomes latent, agreeable to a doctrine which has for some time been 

 taught at Edinburgh by Professor Black ? Or does fire become fixed and 

 quiescent, according to a similar system adopted by Dr. Franklin ?* Air we know 

 exists either in a fixed or elastic state ; and fire may in like manner exist in 

 bodies, either in a latent, fixed, and quiescent; or in a sensible, fluid, and 

 active state. Agreeable to this idea, the bees wax receives the fire in an active 

 state, and dissolves ; while the human body and the albumen ovi, receiving the 

 fire in a latent state, are little altered in their temperature. Let each of these 

 however be put in contact with a different body, tin for instance ; and though 

 the heat of the air continues the same, yet the fire no longer enters in a latent 

 state, but with all its sensible and active powers ; for the albumen ovi suspended 

 in a tin vessel soon coagulates ; and the human body, covered with the same 

 metal, would quickly experience an intolerable and destructive degree of heat. 

 Or are the above phenomena more satisfactorily explained, by considering 

 diff'erent bodies as possessing different conducting powers ; some being 

 strong, others weak conductors of fire? All those bodies then which 

 are weak conductors of fire from air, may be placed in air, without 

 receiving the heat of this medium. Hence the albumen ovi remains fluid 

 in air heated to 224°. Hence likewise the frog, the lizard, the came- 

 lion, &c. retain their natural temperature, and feel cold to the touch, 

 though perpetually surrounded with air hotter than their own bodies. Hence 

 also, the human body keeps nearly its own temperature, in a stove heated to 



• Exper. and Observ. p. 346 and 412. 

 VOL. XIII. 4 T 



