54 8 SCIENCE PROGRESS 



beyond a certain number are made impossible ; it is that 

 property which prevents indefinitely long-continued action 

 and unending response. 



But clearly this same property is possessed by certain 

 chemical systems. Thus dynamite has inertia towards a 

 spark ; it explodes by concussion, not by ignition. 



The extreme molecular instability of certain substances, 

 the picrates, fulminate of mercury or of silver, may certainly 

 be called their affectability towards stimuli tending to cause 

 their disruption, but their possession of this high affectability 

 does not entitle these materials to be called living. 



Affectability is a property not of living matter exclusively, 

 but of many varieties of non-living matter as well : affectability 

 is correctly classified as one of the fundamental properties of 

 protoplasm, but protoplasm is not living matter because it 

 possesses affectability. Living matter also possesses functional 

 inertia, which is the power to disregard or be oblivious to 

 certain kinds of stimuli ; but some kinds of matter that are 

 non-living also possess this property in a high degree. The 

 possession, therefore, of a degree of inertness towards certain 

 forms of stimulation does not distinguish living from non- 

 living substance. Both affectability and functional inertia 

 are vital properties, but they are properties not possessed 

 exclusively by living matter. 



When we pass on to the other characteristics of vitality, 

 we find ourselves on very different ground. 



Living animal bioplasm has the power of growing, that is 

 of assimilating matter in most cases chemically quite unlike 

 that of its own constitution. Now this is a remarkable 

 power, not in the least degree shared by non-living matter. 

 Its very familiarity has blinded us to its uniqueness as a 

 chemical phenomenon. The mere fact that a man eating beef, 

 bird, fish, lobster, sugar, fat and innumerable other things 

 can transform these into human bioplasm, something chemi- 

 cally very different even from that of them which most re- 

 sembles human tissue, is one of the most extraordinary facts 

 in animal physiology. A crystal growing in a solution is not 

 only not analogous to this process, it is in the sharpest possible 

 contrast with it. The crystal grows only in the sense that it 

 increases in bulk by accretions to its exterior, and only does 

 that by being immersed in a solution of the same material as 



