Nature of the Universe 25 



customed in biology to distinguish between living 

 things and material that is not Hving. A man, a dog, 

 a plant, a bacterium — these are living. But a stone, 

 a gas, a mass of molten iron, a burning vapor — these, 

 according to our usual judgment, are not living. It is 

 true that there exist also certain things about which 

 we may be in doubt as to whether they should be 

 considered living or not living. Such are enzymes, 

 such are filtrable viruses. But as between marked 

 cases, as between a man and a stone, as between a bird 

 and a mass of molten iron, there is, in our usual way 

 of viewing these matters, no doubt ; one is living, the 

 other is not. We are accustomed, too, to see the living 

 transformed by certain conditions into the non-living. 

 On this basis, we are accustomed, as a result of ob- 

 servation and experiment, to distinguish conditions in 

 which life may occur from conditions that are incom- 

 patible with life. We find and report in our scientific 

 papers that there are many conditions under which 

 life cannot exist. Indeed, we find and report that life 

 does occur only under a narrow range of conditions. 

 You may find the conditions which limit the occur- 

 rence of life enumerated in any textbook of physi- 

 ology. Among the conditions which are experimentally 

 incompatible with life are high and low temperatures, 

 certain chemical conditions, and a large class of 

 physical conditions. If we subject living things to 

 these conditions, all the characteristic phenomena of 

 life, including the mental phenomena, disappear, and 

 we say that our material is no longer living. 



Are these statements correct .'^ Does our distinction 



