COSMIC PHILOSOPHY 



waste by and by necessitates a recurrence of the 

 rhythm. Thus the alternation of sleep and 

 wakefulness is due to a periodic variation in 

 the ratio between the amount of nerve-force 

 stored up in the cerebrum and the amount 

 stored up in the sympathetic ganglia. We 

 recognize this truth in practice when we seek 

 to induce sleep by stimulating the sympathetic 

 nerve with such substances as bromide of po- 

 tassium. 



The phenomenon of sleep is still further in- 

 teresting as the most familiar instance of the de- 

 pendence of biologic rhythms upon astronomic 

 rhythms. All organisms, animal and vegetable, 

 from the highest to the lowest, exhibit alterna- 

 tions in the total distributions of their forces, 

 which coincide with the periodic appearance and 

 disappearance of sunlight. The longer astrono- 

 mic rhythm, known as the earth's annual revo- 

 lution, causes corresponding rhythms in vege- 

 table and animal life ; witness the blossoming 

 and leafing of plants in the spring, the revival 

 of insect activity at the same season, the peri- 

 odic flights of migratory birds, the hibernating 

 sleep of many vertebrates, and the thickened 

 coats or the altered habits of others that do not 

 hibernate. If we consider the species instead 

 of the individual, we shall find that still longer 

 astronomic rhythms, often complicated by geo- 

 logic rhythms, cause periodic changes in the 

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