Light affects the respiration of animals just as it affects the
respiration of plants. This is novel doctrine, but it is demonstrable.
In the day-time we expire more carbonic acid than during the night; a
fact known to physiologists, who explain it as the effect of sleep: but
the difference is mainly owing to the presence or absence of sunlight;
for sleep, as sleep, _increases_, instead of diminishing, the amount
of carbonic acid expired, and a man sleeping will expire more carbonic
acid than if he lies quietly awake under the same conditions of light
and temperature; so that if less is expired during the night than
during the day, the reason cannot be sleep, but the absence of light.
Now we understand why men are sickly and stunted who live in narrow
streets, alleys, and cellars, compared with those who, under similar
conditions of poverty and dirt, live in the sunlight.--_Blackwood’s
Edinburgh Magazine_, 1858.
The influence of light on the colours of organised creation is well
shown in the sea. Near the shores we find seaweeds of the most
beautiful hues, particularly on the rocks which are left dry by
the tides; and the rich tints of the actiniæ which inhabit shallow
water must often have been observed. The fishes which swim near the
surface are also distinguished by the variety of their colours,
whereas those which live at greater depths are gray, brown, or
black. It has been found that after a certain depth, where the
quantity of light is so reduced that a mere twilight prevails, the
inhabitants of the ocean become nearly colourless.--_Hunt’s Poetry
of Science._