214 ' GENERAL PHYSIOLOGY 



This consideration is very important, for from it there follows a 

 principle of far-reaching significance which usually is not formu- 

 lated with sufficient clearness, viz. : In the combination of atoms 

 kinetic energy is liberated ; in the separation of atoms kinetic energy 

 is absorbed. 



This principle, which is a necessary sequence of the law of the 

 conservation of energy, must be considered as a fundamental one 

 for all chemical transformations, and forms the starting-point for 

 an understanding of all the phenomena connected with the trans- 

 formation of energy within the living organism. That as a rule 

 it has not been established and applied with sufficient clearness, 

 is to be ascribed chiefly to the fact that in certain cases at first sight 

 it suffers apparently an exception. To make the relations clear, 

 this must be considered, at least briefly. 



To express in terms of heat the energy that is transformed in a 

 chemical process, there are recognised processes in which heat is 

 evolved and processes in which heat is absorbed. In accordance 

 with the nomenclature of thermo-chemistry, the heat that is evolved 

 in a chemical process is termed the positive thermo-chemical equiva- 

 lent, the heat that is absorbed, on the other hand, the negative 

 thermo-chemical equivalent. From the above considerations, it 

 would be expected that all synthetic processes, i.e., all processes 

 in which bodies unite, would be accompanied by an evolution of 

 heat, for in every synthesis atoms become united, and in every 

 union of atoms energy is liberated. Vice versa, it would be expected 

 that all decomposition-processes, i.e., all processes in which united 

 atoms become separated, would be accompanied by an absorption of 

 heat. If the conceptions of synthesis and decomposition are employed 

 in their pure significance, this is always the case. Nevertheless, 

 at first sight there appear certain exceptions to the rule. For 

 example, some syntheses are known in chemistry, such as that of 

 hydrogen iodide, which are accompanied by an absorption of heat ; 

 on the other hand, there are many decompositions, especially of the 

 more complex compounds, such as nitroglycerine and other explosives, 

 in which a powerful evolution of energy takes place. These are 

 undeniable facts, but, if the details of these processes be analysed 

 somewhat fully, the apparent paradox becomes at once clear and in 

 reality confirms the law. Since no free atoms are known, but since 

 the similar atoms of every chemical element are united always into 

 molecules, or groups of atoms, it is evident that unless whole mole- 

 cules enter into combination without rearrangement of their atoms 

 or are split off from a combination as preformed groups, then a 

 decomposition of the active molecules into their atoms must precede 

 every synthesis, and a synthesis of the free atoms into new mole- 

 cules must follow every decomposition. Hence, no synthesis occurs 

 without previous decomposition, and no decomposition without 

 subsequent synthesis. Accordingly, it is clear that under certain 

 circumstances heat can be absorbed in a synthesis : for example, 





