FITNESS 35 



which are imposed upon inquiry by assuming 

 complexity, regulation, and metabolism ex- 

 clusively. Perhaps in reality these postu- 

 lates are only two. Metabolism might with- 

 out difficulty be included under regulation, 

 but the consideration of such purely logical 

 questions is beside the present purpose. 

 However, these are probably the character- 

 istics of the organism which are best fitted for 

 discussion in relation to the physico-chemical 

 phenomena of matter and energy, and it is 

 barely possible that no others bear the same 

 simple relations to the outside world. 



York, 1903, Chaps. X and XI, especially the following 

 statement : — 



"The physical conditions on the surface of our earth 

 which appear to be necessary for the development and main- 

 tenance of living organisms may be dealt with under the fol- 

 lowing headings : — 



" 1. Regularity of heat supply, resulting in a limited range 

 of temperature. 



"2. A sufficient amount of solar light and heat. 



" 3. Water in great abundance, and universally distributed. 



"4. An atmosphere of sufficient density, and consisting of 

 the gases which are essential for vegetable and animal life. 

 These are Oxygen, Carbonic-acid gas, Aqueous vapor, Ni- 

 trogen, and Ammonia. These must all be present in suitable 

 proportions. 



"5. Alternations of day and night." 



It must be remembered, however, that such conclusions 

 depend upon reasoning from analogy, a dangerous proceed- 

 ing. 



