INTRODUCTION. XXV11 



as it is said, heat becomes latent that is, the energy of the heat which 

 has become latent is changed into chemical energy, and this, after 

 decomposition of the compound chemical body, is again represented by 

 the chemical affinity between its isolated different atoms. 



Law of the Conservation of Energy. 



Julius Kobert Mayer and Helmholtz have established the important 

 law, that in a system which does not receive any influence and impres- 

 sion from without, the sum of all the forces acting within it is always the 

 same. The various forms of energy can be transformed one into the other, 

 so that Jcinetic energy may be transformed into potential energy and vice versa, 

 but there is never any part of the energy lost. The transformation takes 

 place in such measure that, from a certain definite amount of one form 

 of energy, a definite amount of another can be obtained. 



The various forms of energy acting in organisms occur in the follow- 

 ing modifications : 



1. Molar motion (ordinary movements), as in the movements of the 

 whole body, of the limbs, or of the intestines, and even those observable 

 microscopically in connection with cells. 



2. Movements of Atoms as Heat. We know, in connection with 

 the vibration of atoms, that the number of vibrations in the unit of 

 time determines whether the oscillations appear as heat, light, or 

 chemically-active vibrations. Heat-vibrations have the smallest 

 number, while chemically-active vibrations have the largest number, 

 light-vibrations standing between the two. In the human body, we 

 only observe heat-vibrations, but some of the lower animals are capable 

 of exhibiting the phenomena of light. 



In the human organism, the molar movements in the individual 

 organs are constantly being transformed into heat, e.g., the kinetic 

 energy in the organs of the circulation is transformed by friction into 

 heat. The measure of this is the "unit of work"=I gramme-metre, 

 and the "unit of heat" = 4:25'5 gramme-metres. 



3. Potential Energy. The organism contains many chemical com- 

 pounds which are characterised by the great complexity of their 

 constitution, by the imperfect saturation of their affinities, and hence, 

 by their great tendency to split up into simpler bodies. 



The body can transform the potential energy into heat as well as 

 into kinetic energy, the latter always in conjunction with the former, 

 but the former always by itself alone. The simplest measure of the 

 potential energy is the amount of heat, which can be obtained by complete 

 combustion of the chemical compounds representing the potential 



