192 THE LAW OF BIRTHS AND DEATHS 



that the degree of fertility will be directly proportional 

 to the development of nervous energy until the optimum 

 point for fertility is reached, and will thenceforward 

 vary inversely with the development of nervous energy. 

 The formula must be taken as applying to that condition 

 of the nerves which favours the discharge of energy, and 

 this condition will represent the net result of nutrition 

 and activity, or balance between accumulation and ex- 

 penditure. 



As thus stated, the theory is a working hypothesis, 

 and is merely the best statement of the law of nervous 

 action in this matter that our almost complete ignorance 

 of what goes on in the nerve permits us to make. Its 

 value lies in this, that it produces order out of the chaos 

 of apparently contradictory facts, and enables us to conduct 

 intelligently directed inquiries instead of groping blindly 

 in the dark. It will be subject to restatement in the 

 light of fuller knowledge, and when it can be replaced by 

 a better statement, the quicker it is flung upon the scrap- 

 heap the better. 



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