BOOK VII. 



OF TEE PHYSICAL FORCES IN BIOLOGY. 



CHAPTEK I. 



or ORGANIC HEAT. 



Chemical reactions, which have not for corollary a certain 

 development of heat, are noted as rare exceptions. But life is 

 only maintained by perpetual material exchanges, by combinations 

 and decombinations, incessant molecular mutations ; we must, 

 then, expect to see organised bodies present, during their life, 

 calorific combinations altogether peculiar to them. 



A general fact already results from the thermometric observa- 

 tions gathered in the two living kingdoms ; namely, that the 

 elevation of the temperature is habitually so much the greater 

 in proportion as the organic structure is more complex, more 

 differentiated, rnore perfect. 



Plants nearly follow the thermal variations of the ambient 

 medium. This is the conclusion at which M. Rameaux, of 

 Strasburg, and also M. Becquerel have arrived.^ The first of 

 these observers made holes in the trunks of trees, into which he 

 introduced thermometers ; the second made use of very sensitive 

 thermo-electric apparatus. These observations, however, must 

 only be accepted with caution. We must first of all throw aside 

 hibernal observations. In winter, the life of the vegetal is 

 ^ Des Phiniomines Phyaico-CMnvUpi^. 



