460 BIOLOGY. [BOOK vn. 



the mechanical equivalents with relation to water. A step how- 

 ever has been taken in this direction by determining the heat of 

 combustion of a certain number of bodies. The following table 

 indicates the number of calories developed by the combustion, 

 the oxydation of some simple or compound bodies : 



Kilogrammes of water raised 

 from to 1 degree by com- 



Oxydised Substances. bination with the oxygen 



of 1 kilogramme of each 

 substance. 



Hydrogen 34,135 



Carbon 7,990 



Sulphur 2,263 



Phosphorus 5,747 



Zinc 1,301 



Iron 1,576 



Tin 1,233 



Olefiant Gas 11,990 



Alcohol 7,016 



Inversely, when once these bodies are saturated with oxygen, 

 their decomposition by an electric current necessitates the absorp- 

 tion of a force equivalent to the number of calories which 

 develops their combustion. 



These observations prove that, in principle, the atomic move- 

 ments are included in the general law of the unity of physical 

 forces ; but how powerless they are still to permit us to note 

 exactly all the transformations of the molecular movements 

 which take place in the interior of organised bodies ! 



Without doubt there is, in these last bodies, nothing which 

 does not proceed from, the mineral world ; but these elements of 

 mineral production, in ultimate analysis, group themselves in the 

 living organism into compounds infinitely complex, and in a state 

 of incessant metamorphosis. Though these chemical transforma- 

 tions take place in sufficiently regular series, according to a kind 

 of chemical rhythm, nevertheless it is very difficult to follow them 

 through all their phases, and most frequently we are thereby 

 reduced, in order to form an idea of the chemical acts of organ- 

 isms, to a comparison of the absorbed bodies with the eliminated 



