612 Aquaria: Their Past, Present, and Future. [ October, 
November, 1873, vol. viii., second series, pp. 2757, 2758, was as 
follows: He kept his living marine animals, consisting of the 
lower kinds below fishes, in a number of glass cylindrical jars, 
of various sizes and proportions, and with usually one animal in 
each. The water in these jars he changed every morning, 
“often twice a day, if he perceived the smallest fragment : 
amongst it, wiping and washing the glasses very clean.” He 
then drew away the water so used, and replenished it from the 
earthenware jar with the water got from the sea. At one time 
I should not have termed this aquarium-keeping at all, because 
of the change of water.. (See Crystal Palace Aquarium Hand- 
book, 1875, p. 7.) But now, having got to think more broadly, 
I recognize this, not as a change of water in the sense of its 
being lost, but merely as a change of position from a house in 
Edinburgh to the sea, and back again. That is to say, the 
water he dismissed from his jars went into a gutter in a street, 
or into a sewer below it, and found its way by gravitation into 
the ocean again. Or, if it were poured on the ground, into which 
it soaked, it found its way back to the sea by an infinitely more 
circuitous route. But had Dalyell been more of a general phil- 
osophical thinker as well as a naturalist, be would have saved 
himself this very great amount of cost and trouble. Had he 
but reflected on that which was then known, namely, that water 
— both sea-water and fresh water — is practically indestructible, 
and that any decaying organic matter, animal or vegetable, or 
both mixed, can be got rid of, and the water be left pure, then 
he would have saved his servants their weary walks of more than 
as far, in their aggregation, as twice round the world, nearly. 
In the ocean, of course, various animals and plants are inces- 
santly dying in large numbers, and their decomposing remains 
are prevented from permanently poisoning the water, in which 
other animals live and breathe, by the incessant motion to which 
the sea is subjected, and this: motion brings the water into puri- 
fying contact with the atmospheric air which every where exists. 
It is this air, or rather the oxygen in it, which the water takes 
up in greater quantity than the nitrogen, which is another and 
larger component of the atmosphere, which is the source of pe 
fication alluded to, the water being merely a medium or a vehicle 
for the exhibition of the oxygen. In addition to this, vegeta” 
grows by the action of light, and decomposes the poisonous 
carbonic acid gas evolved by the breathing of animals, the sor 
being used to form the woody substance of the plants, and the 
