24 THE MYSTERY OF LIFE. 



in such phrases as " molecular changes," " phy- 

 sical relations," " modified," " conditioned," and 

 many more. In this way they succeed in en- 

 closing for the time, as it were in a thick mist, 

 the question at issue. 



So, too, some speak of physical energy, 

 and of chemical energy, and of vital energy, as 

 if these were three forms of energy which had 

 been proved to be closely related to each other. 

 Of the chemical and physical forms of energy 

 something is known, but of the relationship of 

 the so-called vital energy nothing has been 

 proved. We only know that the influence it 

 exerts is altogether different from that which has 

 been traced to physical and chemical energy. 



Is it not incorrect to speak of the action 

 of a nerve, or muscle, as being due to vital 

 energy, seeing that the energy in question may 

 be simply physical and chemical, although it is 

 manifested in the tissues of a living being ? 

 The energy is probably of the same nature as 

 the physical and chemical energy manifested by 

 non-living matter out of the body. But if under 

 vital energy it is sought to include formative 

 tissue-producing power, an interpretation is given 

 to the term energy or force, which cannot be justi- 



