ent to perform all functions,
and one and the same portion of protoplasm may successively take on the
function of feeding, moving, or reproducing apparatus. In the highest, on
the contrary, a great number of parts combine to perform each function,
each part doing its allotted share of the work with great accuracy and
efficiency, but being useless for any other purpose.

On the other hand, notwithstanding all the fundamental resemblances that
exist between the powers of the protoplasm in plants and in animals, they
present a striking difference (to which I shall advert more at length
presently), in the fact that plants can manufacture fresh protoplasm out
of mineral compounds, whereas animals are obliged to procure it
ready-made, and hence, in the long run, depend upon plants. Upon what
condition this difference in the powers of the two great divisions of the
world of life depends, nothing is at present known.

With such qualification as arises out of the last-mentioned fact, it may
be truly said that the acts of all living things are fundamentally one. Is
any such unity predictable of their forms? Let us seek in easily verified
facts for a reply to this question. If a drop of blood be drawn by
pricking one's finger, and viewed with proper precautions and under a
sufficiently high microscopic power, there will be seen, among the
innumerable multitude of little circular, discoidal bodies, or corpuscles,
which float in it and give it its color, a comparatively small number of
colorless corpuscles, of somewhat larger size and very irregular shape. If
the drop of blood be kept at the temperature of the body, these colorless
corpuscles will be seen to exhibit a marvelous activity, changing their
forms with great rapidity, drawing in and thrusting out prolongations of
their substance, and creeping about as if they were independent organisms.

The substance which is thus active is a mass of protoplasm, and its
activity differs in detail, rather than in principle, from that of the
protoplasm of the nettle. Under sundry circumstances the corpuscle dies
and becomes distended into a round mass, in the midst of which is seen a
smaller spherical body, which existed, but was more or less hidden, in the
living corpuscle, and is called its _nucleus_. Corpuscles of essentially
similar structure are to be found in the skin, in the lining of the mouth,
and scattered through the whole framework of the body. Nay, more: in the
earliest condi