ii ANIMAL LIFE 129 



in the two cases, but it arrives at the same result. In 

 the first case, it provides the muscle-cell with a large 

 reserve deposited in advance : the quantity of glycogen 

 contained in the muscles is, indeed, enormous in 

 comparison with what is found in the other tissues. 

 In the nervous tissue, on the contrary, the reserve 

 is small (the nervous elements, whose function is 

 merely to liberate the potential energy stored in the 

 muscle, never have to furnish much work at one time) ; 

 but the remarkable thing is that this reserve is restored 

 by the blood at the very moment that it is expended, 

 so that the nerve is instantly recharged with potential 

 energy. Muscular tissue and nervous tissue are, 

 therefore, both privileged, the one in that it is stocked 

 with a large reserve of energy, the other in that it is 

 always served at the instant it is in need and to the 

 exact extent of its requirements. 



More particularly, it is from the sensori-motor 

 system that the call for glycogen, the potential 

 energy, comes, as if the rest of the organism were 

 simply there in order to transmit force to the nervous 

 system and to the muscles which the nerves control. 

 True, when we think of the part played by the nervous 

 system (even the sensori-motor system) as regulator 

 of the organic life, it may well be asked whether, in this 

 exchange of good offices between it and the rest of the 

 body, the nervous system is indeed a master that the 

 body serves. But we shall already incline to this hypo 

 thesis when we consider, even in the static state only, 

 the distribution of potential energy among the tissues ; 

 and we shall be entirely convinced of it when we reflect 

 upon the conditions in which the energy is expended 

 and restored. For suppose the sensori-motor system 

 is a system like the others, of the same rank as the 



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