THE FOUR LAWS OF AGE 233 



cities. We can follow the changing structure with 

 the microscope. We can gain some knowledge of it 

 by our present chemical methods. Fragmentary as 

 that knowledge is, nevertheless, it suffices to show to us 

 that the condition of the living material is essential and 

 determines what the living material can do. I should 

 like to insist for a moment upon this conception, be- 

 cause it is directly contrary to a conception of living 

 material which has been widely prevalent in recent 

 years, much defended and popularly presented on 

 many different occasions. The other theory, the one 

 to which I cannot subscribe, may perhaps be most 

 conveniently designated by the term the theory of 

 life units. It is held by the defenders of this faith 

 that the living substance contains particles, very small 

 in size, to which the vital properties are especially 

 attached. They look at a cell and find that it has 

 water, or water containing a small amount of salts in 

 solution, filling up spaces between the threads of pro- 

 toplasm. Water is not alive. They see in the proto- 

 plasm granules of one sort and another, in plants 

 chlorophyll, in animals perhaps fat or some other 

 material. That is not living substance, and so they 

 go, striking out from their conception of the living 

 material in the cell one after another of these com- 

 ponent parts until they get down to something very 

 small, which they regard as the life unit. I do not 

 believe these life units exist. It seems to me that all 

 these dead parts, as this theory terms them, are parts 

 of the living cell. They are factors which enable the 



