BALANCE OF ANIMAL AND VEGETABLE LIFE. 103 
another, which constitutes his food in some stage of his life, 
and this other again may be as injurious to some plant as his 
destroyer is beneficial to another. The equation of animal and 
vegetable life is too complicated a problem for human intel¬ 
ligence to solve, and we can never know how wide a circle of 
disturbance we produce in the harmonies of nature when we 
throw the smallest pebble into the ocean of organic life. 
This much, however, we seem authorized to conclude: as 
often as we destroy the balance by deranging the original pro¬ 
portions between different orders of spontaneous life, the law 
of self-preservation requires us to restore the equilibrium, by 
either directly returning the weight abstracted from one scale, 
or removing a corresponding quantity from the other. In 
other words, destruction must be either repaired by repro¬ 
duction, or compensated by new destruction in an opposite 
quarter. 
The parlor aquarium has taught even those to whom it is 
but an amusing toy, that the balance of animal and vegetable 
life must be preserved, and that the excess of either is fatal to 
the other, in the artificial tank as well as in natural waters. 
A few years ago, the water of the Cochituate aqueduct at 
Boston became so offensive in smell and taste as to be quite 
unfit for use. Scientific investigation found the cause in the 
too scrupulous care with which aquatic vegetation had been 
excluded from the reservoir, and the consequent death and 
decay of the animalcule which could not be shut out, nor live 
in the water without the vegetable element.* 
* It is remarkable that Palissy, to whose great merits as an acute 
observer I am happy to have frequent occasion to bear testimony, had 
noticed that vegetation was necessary to maintain the purity of water in 
artificial reservoirs, though he mistook the rationale of its influence, which 
he ascribed to the elemental “ salt ” supposed by him to play an important 
part in all the operations of nature. In his treatise upon Waters and 
Fountains, p. 174, of the reprint of 1844, he says: “And in special, thou 
shalt note one point, the which is understood of few: that is to say, that 
the leaves of the trees which fall upon the parterre, and the herbs growing 
beneath, and singularly the fruits, if any there be upon the trees, being 
decayed, the waters of the parterre shall draw unto them the salt of the 
