176 ANIMALS AND PLANTS vi 



which contains many million times the weight of 

 the original spore, in protein compounds and 

 cellulose. Thus we have a very wide basis of fact 

 for the generalisation that plants are essentially 

 characterised by their manufacturing capacity — by 

 their power of working up mere mineral matters 

 into complex organic compounds. 



Contrariwise, there is a no less wide foundation 

 for the generalisation that animals, as Cuvier puts 

 it, depend directly or indirectly upon plants for 

 the materials of their bodies ; that is, either they 

 are herbivorous, or they eat other animals which 

 are herbivorous. 



But for what constituents of their bodies are 

 animals thus dependent upon plants ? Certainly 

 not for their horny matter ; nor for chondrin, the 

 proximate chemical element of cartilage ; nor for 

 gelatine ; nor for syntonin, the constituent of 

 muscle; nor for their nervous or biliary sub- 

 stances; nor for their amyloid matters; nor, 

 necessarily, for their fats. 



It can be experimentally demonstrated that 

 animals can make these for themselves. But that 

 which they cannot make, but must, in all known 

 cases, obtain directly or indirectly from plants, is 

 the peculiar nitrogenous matter, protein. Thus 

 the plant is the ideal proUtaire of the living 

 world, the worker who produces ; the animal, the 

 ideal aristocrat, who mostly occupies himself in 

 consuming, after the manner of that noble repre- 



