i> 72 AGE, GROWTH, AND DEATH 



To explain life we must discover why it displays itself only in 

 a physical basis composed of various albumenoid molecules, 

 imbibed with water and certain salts, and commingled with other 

 complex organic compounds, all disposed in a definite order; 

 why this basis divides into distinct masses, cells, grouped each 

 around a distinct body, the nucleus ; why chemical and physical 

 events take place in a particular order in each cell, the regulating 

 power being within the cell itself; why senescence and rejuvena- 

 tion take place ; and finally the sources of consciousness, memory, 

 and habit. No mechanical explanation, or theory of conscious 

 automatism suffices, but a vital force is the only reasonable 

 hypothesis; the nature of that force is, for the present, an entire 

 mystery, and before we can expect to discover it we must settle 

 what are the phenomena to be explained by it. 



[From the Proceedings of the American Association for the Advancement of 

 Science, vol. xxviii., Saratoga Meeting, August, 1879.] 



