EVOLUTION OF HEAT. 621 



a close box, from which the head projected (in order to avoid the direct in- 

 fluence of the heated air on the temperature of the mouth), the air had pro- 

 bably become charged with the vapor exhaled from the surface, and had, 

 therefore, somewhat of the effects of a moist atmosphere. At any rate, the 

 temperature of the body does not appear to rise, under any circumstances, to a 

 degree very much greater than this. In one of the experiments of Drs. Fordyce 

 and Blagden, 1 the temperature of a Dog, that had been shut up for half an hour 

 in a chamber of which the temperature was between 220 and 236, was found 

 to have risen from 101 to about 108. MM. Delaroche and Berger tried 

 several experiments on different species of animals, in order to ascertain the 

 highest temperature to which the body could be raised without the destruction 

 of life, by inclosing them in air heated from 122 to 201, until they died: the 

 result was very uniform, the temperature of the body at the end of the experi- 

 ment only varying in the different species between 11 and 13 above their 

 natural standard : whence it may be inferred that an elevation to this degree 

 must be fatal. This elevation would be attained comparatively soon in a moist 

 atmosphere; partly because of the greater conducting power of the medium; 

 but principally on account of the check which is put upon the vaporization of 

 the fluid secreted by the skin. Even here, however, custom and acquired con- 

 stitution have a very striking influence; for whilst the inhabitants of this 

 country are unable to sustain, during more than 10 or 12 minutes, immersion 

 in a vapor-bath of the temperature of 110 or 120, the Finnish peasantry re- 

 main for half an hour or more in a vapor-bath the temperature of which finally 

 rises even to 158 or 167. Accurate experiments are yet wanting to deter- 

 mine the influence of humidity on the effects of cold air. From experiments 

 on young Birds incapable of maintaining their own temperature, of which some 

 were placed in cold dry air, and others in cold air charged with moisture, it was 

 found by Dr. Edwards that the loss of heat was in both instances the same ; 

 the effect of the evaporation from the surface in the former case being counter- 

 balanced in the latter by the depressing influence of the cold moisture. This 

 influence, the existence of which is a matter of ordinary experience, is probably 

 exerted directly upon the nervous system. 



655. Having thus considered the general facts which indicate the faculty 

 possessed by the living system, in the higher Animals, of keeping up its temper- 

 ature to an elevated standard, and of preventing it from being raised much 

 beyond it by any degree of external heat, we have next to inquire to what this 

 faculty is due. In forming an opinion upon this point, it is of fundamental 

 importance to bear in mind that the production of Heat is not peculiar to Ani- 

 mals, but is exhibited also by Plants, in parts in which certain vital operations 

 that involve the production of carbonic acid, are taking place with unusual 

 rapidity, and under circumstances which tend to prevent the dissipation of the 

 heat thus generated. This is pre-eminently the case during the periods of germ- 

 ination and flowering ; as may be seen in the act of malting, where a number 

 of germinating seeds being heaped together, the thermometer in the midst of 

 them has been observed to rise to 110; whilst during the flowering of the 

 Arum tribe, whose blossoms are crowded together on spadixes, and these are 

 inclosed in protective spathes, a thermometer placed in the midst of twelve 

 spadixes has been seen to rise to 121, the temperature of the surrounding air 

 being only 66. a In all such cases, the elevation of temperature is found to be 

 a very constant ratio to the amount of carbonic acid which is produced by the 

 union of atmospheric oxygen with carbon set free from the vegetable tissues; 3 



1 "Philosophical Transactions," 1775. 



2 See "Princ. of Phys., Gen. and Comp.," $ 615, 616, Am. Ed. 



3 This has been made yet more certain by the recent observations of M. Garreau (" Ann. 

 des Sci. Nat.," 3me serie, Botan., torn. xvi. p. 250), who has noted the temperature of 



