HEAT OF ANIMALS AND PLANTS. 427 



HOf in Tetanus ; whilst it has fallen to 82 in Spasmodic Asthma, and 

 to 77 in Cyanosis and Asiatic Cholera. 



762. In searching for the conditions on which this production of heat 

 within the Animal body is dependent, it is very important to hear in 

 mind, that a similar generation of Caloric may be observed in the Vege- 

 table kingdom. It appears from the most recent and exact experi- 

 ments, that all living Plants are somewhat warmer than similar dead' 

 plants exposed to the same atmosphere ; and that the elevation is the 

 greatest in the leaves and young stems, in which the most active vital 

 changes are taking place. But the most decided production of heat 

 occurs in the flowering of certain Plants, such as the Arum, which 

 have large fleshy receptacles, on which a great number of blossoms are 

 crowded ; thus a thermometer placed in the centre of five spadixes of 

 the Arum cordifolium has been seen to rise to 111, and one placed in 

 the midst of twelve spadixes has risen to 121, whilst the temperature 

 of the surrounding air was only 66. In the germination of seeds, also, 

 a great elevation of temperature occurs, which is rendered most evident 

 by bringing together a number of seeds, as in the process of malting, so 

 that the caloric is not dissipated as fast as it is generated ; the ther- 

 mometer, placed in N the midst of a mass of seeds in active germination, 

 has been seen to rise to 110. 



763. Thus it is evident that the chemical changes which are involved 

 in the operations of Nutrition, are capable of setting free a large amount 

 of heat ; which, although ordinarily dissipated from the vegetating sur- 

 face too speedily to manifest itself, becomes sensible enough, when this 

 rapid loss is checked. If we further examine into the nature of the 

 chemical changes which appear most concerned in this elevation of 

 temperature, we find that they uniformly consist in the combination of 

 the carbon of the plant with the oxygen of the atmosphere ; so that a 

 large quantity of carbonic acid is formed and set free, precisely in the 

 manner of the Respiration. of Animals. This process is so slowly per- 

 formed, in the ordinary growth of Plants, that it is concealed (as it 

 were) by the converse change, the fixation of carbon from the carbonic 

 acid of the atmosphere, under the influence of light ( 83). But it takes 

 place with extraordinary energy during flowering and germination ; a 

 large quantity of carbon being set free, by union with the oxygen of the 

 air ; and the starchy matter of the receptacle, or of the seed, being con- 

 verted into sugar. Now it has been ascertained by/careful experiments, 

 that the amount of heat generated is in close relation with the amount 

 of carbonic acid set free ; and that, if the formation of the latter be pre- 

 vented, by placing the flower or the seed in nitrogen or hydrogen, no 

 elevation of temperature takes place ; whilst, if the process be stimu- 

 lated by pure oxygen, so that a larger proportion of carbonic acid is 

 evolved, the elevation of temperature is more rapid and considerable 

 than usual. 



764. Upon examining into the conditions under which Caloric is gene- 

 rated in the Animal body, we find them essentially the same. "Wherever 

 the temperature of the body is maintained at a regular standard, so as 

 to be independent of variations in the warmth of the surrounding me- 

 dium, we find a provision for exposing the blood most freely to the in- 



