A Theory of Sleep. 



By Professor A. L. Herrera. 



Sleep is not peculiar to man, for it presents itself in every organism. 

 " Protozoa themselves sleep," says Milne Edwards, and sleep must, 

 therefore, have quite a general cause. Some substances (narcotics, 

 anaesthetics) provoke sleep either by dehydration or by producing con- 

 gestion in the nervous centres, etc. On the other hand, sleep does not 

 invade every organ in the same manner ; it presents itself sporadically in 

 such organs as happen to be extremely tired, or in those that are not 

 well fed. It does not, in short, essentially differ from hibernal sleep. 



Let us seek then for a philosophical explanation comprising every 

 particular case and requiring no suppositions nor vitalistic theories. I 

 find but one entirely general cause : the delay of the protoplasmic 

 currents in which life consists, as I stated in a special paper on this 

 subject. 1 



The Sleep of Plants. 



In animals sleep is characterised by the flaccidity of their 

 locomotor organs, whilst leaves remain in their nocturnal state on 

 account of a very remarkable rigidity that seizes them. Linnaeus once 

 received from Prof. Sauvageau of Montpellier a shoot of Lotus ornitho- 

 podioides L., which began to nourish in a hot-house at the garden of 

 Upsala. The great botanist examined the flowers directly they opened 

 and observed that they disappeared on the same night. He believed 

 at first that they had been thoughtlessly cut away, but had to acknow- 

 ledge his mistake next day, as the disappearance of the flowers at 

 night depends completely on the close approach of the adjoining 

 leaves which form a kind of shelter for them. This observation 

 afforded cause for fresh investigations, and it was discovered that 

 every species of plants opens and shuts itself at an appointed hour, etc. 



Explanation. — " The motor dilatation occurring in some leaves at 

 the base of the petiole is due to two antagonistic factors, the one 

 tending to raise the leaf, the other trying to bend it, but the former, 

 being by nature the weakest, acquires an additional force whenever 



1 "Protoplasmic Currents and Vital Force," Natural Science, April 1899. 



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