THE WONDER OF LIFE 497 



of general biological facts. All activity implies a using 

 up of material, a using up of oxygen, and the formation 

 of waste-products. The nerve cells are in no way exempted, 

 and it has been demonstrated visually that the brain-cells 

 of a bee that has been working hard all day are in a different 

 condition from those in a brain that has been restiag. 

 In a case of prolonged insonmia there was said to be a 

 disappearance of a readily stainable (chromatophilous) 

 substance located in what are called ' Nissl's granules ' 

 in most nerve-cells. Moreover, the nerve- cells require to 

 keep up a store of intra-molecular oxygen. And besides 

 carbonic-acid gas, which is always being removed by the 

 blood, there are subtler wastes, ' fatigue toxins ', about 

 which we do not know very much. The general biological 

 view is therefore this, that persistent activity involves 

 using up of material and oxygen and an accumulation of 

 waste-products, such that the ' machinery ' has to go more 

 slowly, so that re-stoking and cleaning may be thoroughly 

 effected. It is conceivable, indeed, that it might have been 

 arranged that repair always kept pace with waste, and that 

 the organism never got into any physiological arrears at 

 all. It is probable that very simple organisms, such as the 

 ' immortal ' Amoeba are in this happy state. But with 

 increasing complexity this ceased to be possible, and sleep 

 was invented. ' Blessed be the man ', said Sancho Panza, 

 ' who invented sleep ', but we do not know at what precise 

 level of organization the invention was discovered. Prob- 

 ably not until the cerebral cortex was well difEerentiated. 



The general biological theory is consistent with many 

 famihar facts : — ^The greatly fatigued organism falls asleep ; 

 it awakens from sleep refreshed. And it is remarkably 

 confirmed by Legendre's deUcate experiment of injecting 



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