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various other animals, supply good examples of such cells ; but 
the most striking instance is that afforded by the “ white cor- 
puscles ” of the blood. If, namely, we examine the blood of 
man, or of any of the higher vertebrates, under a sufficiently 
high magnifying power, and with suitable precautions, we 
shall observe that it contains floating in it a number of 
minute masses of naked protoplasm, which are provided with 
a nucleus, but are destitute of a proper cell-wall. These are 
the so-called “ white corpuscles/'’ and they are now well 
known as exhibiting the surprising phenomenon that they 
throw out external filaments, or processes of their own pro- 
toplasmic substance, which can be thrust out at any point 
of the surface, and can be again retracted, and which pre- 
cisely resemble the “ pseudopodia ” of such a Rhizopod as 
the Amoeba. Moreover, not only is the life of the (C white 
blood-corpuscles ” in one sense a semi-independent one, but 
these little aggregations of protoplasm are capable of using 
the pseudopodia just as the Amoeba does, not only for 
locomotion but also for the purpose of obtaining food. 
Thus, by adding a little vermilion, or aniline-blue, or milk, 
to a drop of blood, the white corpuscles can be observed 
under the microscope to take in the particles of these sub- 
stances by means of the pseudopodia, and then in some 
cases to discharge them again, in a manner precisely similar 
to that observable in the Amoeba. 
Before proceeding further it should be noted, that all forms 
of vital activity, of whatsoever nature, are attended with a 
certain disintegration and destruction of the living matter, or 
protoplasm, of which the organism is composed. In the case 
of the microscopic unicellular organisms, this constant des- 
truction of life-matter can be inferred rather than actually 
demonstrated ; but in the higher animals and plants it can be 
shown that the vital processes resolve themselves, roughly 
speaking, into the constantly-proceeding destruction of old 
cells, and the corresponding production of new cells to take 
the place of the former. 
Having now considered some of the principal forms in 
which protoplasm presents itself for our examination, and 
some of the chief phenomena which it manifests when alive, 
we may here briefly summarise the essential phenomena 
manifested by all living bodies, as opposed to those which 
are dead. 
1. All living beings may be regarded as essentially larger 
or smaller aggregates of a substance of extreme chemical 
complexity, which is, during life, in a condition of continual 
flux and constant change affecting its minutest parts. In 
VOL. xiv. u 
