LIFE IN OTHER WORLDS. 27 



'vital force/ an influence (sometimes regarded as external) which 

 modifies the behavior of matter and energy without affecting their 

 quantity. But as we can not exclude the probability of similar direct- 

 ing and modifying influences in the inorganic world, it is best pro- 

 visionally to regard the causes of life as present alike in living and not- 

 living substances — conspicuous in living substance because coordinated, 

 but hardly observed in not-living substance, owing to incoordination. 

 If a simile be needed, it may be found in the behavior of light: for 

 certain properties of light, though ever present, become evident only 

 when coordinated by polarization; and polarization, be it noted, is a 

 purely physical action. 



While every element present in living substance may assist in the 

 work, the energy-traffic is carried on chiefly amongst the four elements, 

 nitrogen, oxygen, carbon and hydrogen. Nitrogen is remarkable for 

 the instability of its chemical compounds — the readiness with which 

 they change their composition — and there is little doubt that on this 

 property depends the extreme sensitiveness of living substance. Car- 

 bon and hydrogen have the property of combining together to build up 

 complex compounds, with great storage of potential energy; whereas 

 the same compounds during their oxidation expend their energy in the 

 form of mechanical work, heat, etc. The energy traffic consists of two 

 alternating phases : (1) the accumulation of energy, or 'anabolic' phase, 

 which is always coincident with deoxidation and the formation of com- 

 plex chemical compounds: and (2) the dispersion of energy, or *cata- 

 bolic' phase, coincident with oxidation of the complex substances, 

 which are thereby converted into simpler substances, as carbonic acid 

 and water. In these processes nitrogen is intimately concerned: it is 

 believed to act as the carrier, taking up each element or group of ele- 

 ments and passing it on in a new state of combination. 



All the energy of life is derived ultimately from the sun. A little 

 of this comes indirectly through lightning, which in passing through 

 the air forms ammonia and oxides of nitrogen. These, being carried 

 by rain into the ground, are the constant source of nitrogen for vege- 

 table, and indirectly for animal life. A much larger quantity of energy 

 is well known to be taken direct from the sunshine by plants and used 

 in their anabolic processes. This energy is appropriated by animals in 

 their food ; and whether in the vegetable or in the animal, it assists in 

 many alternations of anabolism and catabolism before it is completely 

 dispersed. 



The range of temperature suited to terrestrial life is comparatively 

 narrow. All vital actions are suspended temporarily, some perma- 

 nently, if subjected to a temperature near the freezing point; while 

 the highest that most organisms can bear lies somewhere between 35° 

 and 45° Centigrade (95° and 113° Fahrenheit). Only the spores of 

 certain bacteria can survive boiling. It is therefore probable that if 



