A Theory of Sleep. 
By Proressor 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.’ 
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 flourish 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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