526 



SCIENCE 



[N. S. Vol. XXXIX. No. 1006 



It seems to be true (one may note in pass- 

 ing) that with the progress of science the 

 term mechanism has come to mean merely any 

 active system. In what follows I shall, there- 

 fore, use the word mechanism in this sense. 

 According to this definition the mechanistic 

 explanation of a phenomenon is simply its 

 explanation as the activity of a system, and 

 this is the only explanation known to physical 

 science. 



Finally, in addition to its material, spatial, 

 and energetic characteristics a system must 

 also be characterized as a whole and in its 

 parts, in its form, structure, and activity by 

 durability. The consideration as well of time 

 as of activity permits the transition from the 

 statical to the dynamical. 



In short, form and size, physical and chemi- 

 cal constitution, activity and duration are the 

 general factors to be considered in any phe- 

 nomenon whatsoever. In the complete descrip- 

 tion of any mechanism all must be considered, 

 but, for the purposes of physical science no 

 others need be, or indeed can be, introduced. 



It is accordingly possible, without any ex- 

 amination of the results of biology, and even 

 in complete ignorance thereof, to investigate 

 the fitness of the special properties of matter 

 for any mechanism, i. e., for mechanism in 



THE SYSTEM 



The fundamental characteristics of a system 

 are the components, the phases, the concentra- 

 tions, and further temperature and pressure. 

 Hence fitness for anp system involves the pos- 

 sibility of the greatest number and variety of 

 components and phases, of the widest ranges 

 of concentrations, temperatures and pres- 

 sures. It has been shown in " The Fitness of 

 the Environment" that the number of possi- 

 ble components (chemical compounds) con- 

 sisting of carbon, hydrogen and oxygen is far 

 greater than in the ease of other elements; 

 that the meteorological cycle mobilizes on 

 land and sea far greater numbers of other 

 elements than would be the case if water were 

 not the active agent in the process; that an 

 aqueous solution is capable of holding a far 

 greater number of components in far greater 



concentrations than can any other; that water 

 makes possible, through its unique thermal 

 properties and its unique qualifications in re- 

 lation to colloids, the greatest possible number 

 and variety of phases. Moreover, many other 

 similar facts have been established without 

 coming upon an unfavorable instance or excep- 

 tion in the course of prolonged search. As for 

 wide ranges of temperature and pressure, they 

 may be passed by, for as a rule such conditions 

 are not consistent with durability, hence their 

 importance is very restricted. 



ACTIVITY 



Any activity is possible provided a suitable 

 system exists and provided suitable energy is 

 present. This fact leads us back to the con- 

 clusion that chemical transformations of hy- 

 drogen, oxygen and carbon are the very best 

 chemical means of storing and liberating 

 energy, and that the reactions of organic com- 

 pounds permit the most delicate adjustments 

 of such transformations. Further it has been 

 shown that the unique thermal properties of 

 water are most highly suited to the storing and 

 distribution of energy, while its solvent power 

 facilitates osmotic pressure and diffusion. It 

 may also be mentioned as a final instance of 

 fitness for activity, among many other ex- 

 amples, that the electro-chemical character- 

 istics of water are in many ways the best pos- 

 sible sources of electrical activity. 



DURABILITY 



Durability depends upon stability of condi- 

 tions and upon supplies of matter and energy 

 to replace what is used up. 



The stability of physico-chemical conditions, 

 which is due to the presence of water and car- 

 bonic acid as primary constituents of the en- 

 vironment, is very great indeed, and, beyond 

 doubt, far greater than what could exist if 

 these substances were replaced by any others. 

 A very large part of all the data of ocean- 

 ography and meteorology do but illustrate the 

 almost inconceivable efficiency with which 

 water, in the main through its unique thermal 

 properties, completely checks very wide ranges 

 of temperature, and as a rule restricts the 



