XXV111 INTRODUCTION. 



energy. The number of work-units can then be calculated from the 

 amount of heat produced. 



4. The phenomena of electricity, magnetism, and diamagnetism 

 may be recognised in two directions, as movements of the smallest 

 particles, which are recognised in the glowing of a thin wire when it 

 is traversed by strong electrical currents (against considerable resist- 

 ance), and also as molar movement, as in the attraction or repulsion of 

 the magnetic needle. Electrical phenomena are manifested in our 

 bodies by muscle, nerve, and glands, but these phenomena are rela- 

 tively small in amount when compared with the other forms of energy. 

 It is not improbable that the electrical phenomena of our bodies 

 become almost completely transformed into heat. As yet experiment 

 has not determined with accuracy a "unit of electricity," directly 

 comparable with the "heat-unit" and the "work-unit." 



It is quite certain that within the organism, one form of energy can 

 be transformed into another form, and that a certain amount of one 

 form will yield a definite amount of another form; further, that new 

 energy never arises spontaneously, nor is energy, already present, ever 

 destroyed, so that in the organism the law of the conservation of 

 energy is continually in action. 



Animals and Plants. 



The animal body contains a quantity of chemically-potential energy 

 stored up in its constituents. The total amount of the energy present 

 in the human body might be measured, by burning completely an entire 

 human body in a calorimeter, and thereby determining how many heat- 

 units are produced when it is reduced to ashes (see Animal Heat, 

 p. 422). 



The chemical compounds containing the potential energy are 

 characterised by the complicated relative position of their atoms, by a 

 comparatively imperfect saturation of the affinities of their atoms, by 

 the relatively small amount of oxygen which they contain, by their 

 great tendency to decomposition, and the facility with which they 

 undergo it. 



If a man were not supplied with food, he would lose 50 grammes of 

 his body-weight every hour ; the material part of his body, which 

 contains the potential energy, is used up, oxygen is absorbed, and a 

 continual process of combustion takes place; by the process of com- 

 bustion, simpler substances are formed from the more complex 

 compounds, whereby potential is converted into kinetic energy. It is 

 immaterial whether the combustion is rapid or slow ; the same amount 



