CHAPTER XXIV. 1 



ON THE RELATION OF LIFE TO OTHER FORCES. 



AN enumeration of theories concerning the nature of life would be 

 beside the purpose of the present chapter. They are interesting as 

 marks of the way in which various minds have been influenced by the 

 mystery which has always hung about vitality; their destruction is but 

 another warning that any theory we can frame must be considered only 

 a tie for connecting present facts, and one that must yield or break on 

 any addition to the number which it is to bind together. 



Before attention had been drawn to the mutual convertibility of the 

 various so-called physical forces heat, light, electricity, and others 

 and until it had been shown that these, like the matter through which 

 they act, are limited in amount, and strictly measurable; that a given 

 quantity of one force can produce a certain quantity of another and no 

 more; that a given quantity of combustible material can produce only a 

 given quantity of steam, and this again only so much motive power; it 

 was natural that men's minds should be satisfied with the thought that 

 vital force was some peculiar innate power, unlimited by matter, and al- 

 together independent of structure and organization. The comparison of 

 life to a flame is probably as early as any thought about life at all. And 

 so long as light and heat were thought to be inherent qualities of certain 

 material which perished utterly in their production, it is not strange 

 that life also should have been reckoned some strange spirit, pent up in 

 the germ, expending itself in growth and development, and finally de- 

 clining and perishing with the body which it had inhabited. 



With the recognition, however, of a distinct correlation between the 

 physical forces, came as a natural consequence a revolution of the com- 

 monly accepted theories concerning life also. The dictum, so long 

 accepted, that life was essentially independent of physical force began 

 to be questioned. 



As it is well-nigh impossible to give a definition of life that shall be 

 short, comprehensive, and intelligible, it will be best, perhaps, to take 



1 This chapter is a reprint, with some verbal alterations, of an essay contrib- 

 uted to St. Bartholomew's Hospital Reports, 1867, 1869, by W. Morrant Baker. 



