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binations, and of uniting them into ternary and quaternary 
organic compounds (chlorophyll, starch, albumen, &c.) the sim- 
plest Protozoon, in common with the highest member of the 
animal kingdom, seems utterly destitute of any such power, 
and is dependent for its support upon organic substances pre- 
viously elaborated by other beings. But, further, the Proto- 
phyte obtains its nutriment by mere absorption of liquid and 
gaseous molecules, which penetrate by simple imbibition; whilst 
the Protozoon, though destitute of any proper stomach, makes 
(so to speak) a stomach for itself in the substance of its body, 
into which it ingests the solid particles that constitute its food, 
and within which it subjects them to a regular process of 
digestion. Hence these simplest members of the two king- 
doms, which can scarcely be distinguished from each other 
by any structural character, seem to be physiologically sepa- 
rable by the mode in which they perform those actions wherein 
their life most essentially consists.” 
Again, in his Animal Physiology (ed. 1859), p. 144, he 
observes : — “ The nature of the food of animals is as various 
as the conformation of their different tribes. It always con- 
sists, however, of substances that have previously undergone 
organisation There are many instances in which, no 
obvious supplies of food being afforded, the mode of sustenance 
is obscure ; and it has been frequently supposed that, in such 
cases, the animals are sustained by air and water alone. But 
it will always be found that, where food is taken in no other 
way, a supply of the microscopic forms of animal or vegetable 
life is introduced by ciliary action ; and it is on these, indeed, 
that a large proportion of the lower forms of aquatic animals 
depend entirely for their support.” 
These testimonies will suffice for the fact; let us now try to 
set before our minds its significance. Let us try and get rid 
of the deadening effect of our familiarity with it. In making 
war one main point is admitted to be the feeding of the army. 
In nature the main point is obviously the same. When you 
have peopled a planet with varied forms of life, the most 
pressing question is, how are they to be fed ? And this is 
answered not by an aggregation of dead nutritive matter, 
which must be exhausted sooner or later, but by the constant 
processes of growth, by a living laborator} 7 incessantly engaged 
in manufacturing food. There is something grand and over- 
powering in this unceasing universal toil, carried on, if we 
regard the planet as a whole, without a moment’s intermission, 
from year to year, from century to century. Not only does 
this activity go on in favourable places, on plains and hill-sides ; 
but in the sea, in lakes and rivers, on the verge of eternal 
