466 
NATURE 
[SEPTEMBE!Y 14, 1899 
It is a very old quest, the quest after the knowledge of the 
nature of living beings, one of the earliest on which man set 
out ; for it promised to lead him to a knowledge of himself, a 
promise which perhaps is still before us, but the fulfilment of 
which is as yet far off. As time has gone on, the pursuit of natural 
knowledge has seemed to Jerd man away from himself into the 
furthermost parts of the universe, anu into secret workings of 
nature in which he appears to be of little or no account ; and 
his knowledge of the nature of living things. and so of his own 
nature, has advanced slowly, waiting till the progress of other 
branches of natural knowledge can bring it aid. Vet in the 
past hundred years, the biologic sciences, as we now call them, 
have marched rapidly onward. 
We may look upon a living body as a machine doing work in 
accordance with certain laws, and may seek to trace out the 
working of the inner wheels, how these raise up the lifeless dust 
into living matter, and let the living matter fall away again into 
dust, giving ont movement and heat. Or we may look upon 
the individual life as a link in a long chain, joining something 
which went before to something about to come, a chain whose 
beginning lies hid in the farthest past, and may seek to know 
the ties which bind one life to another. As we call up to view 
the long series of living forms, living now or flitting like shadows 
on the screen of the past, we may strive to lay hold of the in- 
fluences which fashion the garment of life. Whether the prob- 
lems of life are looked upon from the one point of view or the 
other, we to-day, not biologists only, but all of us, have gained 
a knowledge hidden even from the philosophers a hundred years 
ago. 
Of the problems presented by the living body viewed as a 
machine, some may be spoken of as mechanical, others as 
physical, and yet others as chemical. while some are, apparently 
at least, none of these. In the seventeenth century William 
Harvey, laying hold of the central mechanism of the blood 
stream, opened up a path of inquiry which his own age and the 
century which followed trod with marked success. The know- 
ledge of the mechanics of the animal and of the plant advanced 
apace ; but the physical and chemical problems had yet to wait. 
The eighteenth century, it is true, had its physics and its 
chemistry ; but, in relation at least to the problems of the living 
being, a chemistry which knew not oxygen and a physics which 
knew not the electricity of chemical action were of little avail. 
The philosopher of 1799, when he discussed the functions of 
the animal or of the plant involving chemical changes, was fain 
for the most part, as were his predecessors in the century before, 
to have recourse to such vague terms as ‘‘ fermentation” and the 
like ; to-day our treatises on physiology are largely made up of 
precise and exact expositions of the play of physical agencies 
and chemical bodies in the living organism. He made use of the 
words ‘‘ vital force” or ‘* vital principle,’’ not as an occasional, 
but as a common explanation of the phenomena of the living 
body. During the present century, especially during its latter 
half, the idea embodied in those words has been driven away 
from one seat after another; if we use it now when we are 
dealing with the chemical and physical events of life we use it 
with reluctance, as a deus ex machina to be appealed to only 
when everything else has failed. 
Some of the problems—and those, perhaps, the chief prob- 
lems—of the living body have to be solved neither by physical 
nor by chemical methods, but by methods of their own. Such 
are the problems of the nervous system. In respect to these the 
men of 1799 were on the threshold of a pregnant discovery. 
During the latter part of the present century, and especially 
during its last quarter, the analysis of the mysterious pro- 
cesses in the nervous system which issue as feeling, thought, 
and power to move, has been pushed forward with a 
success conspicuous in its practical, and full of promise 
in its theoretical, gains. That analysis may be briefly de- 
scribed as a following up of threads. We now know that 
what takes place along a tiny thread which we call a nerve-fibre 
differs from that which takes place along its fellow-threads, that 
differing nervous impulses travel along different nerve-fibres, and 
that nervous and psychical events are the outcome of the clash- 
ing of nervous impulses as they sweep along the closely-woven 
web of living threads of which the brain is made. We have 
learnt by experiment and by observation that the pattern of the 
web determines the play of the impulses, and we can already 
explain many of the obscure problems, not only of nervous 
disease, but of nervous life, by an analysis which is a tracking 
out the devious and linked paths of nervous threads. The 
NO. 1559, VOL. 60] 
very beginning of this analysis was known in 1799. Men knew 
that nerves were the agents of feeling and of the movements 
of muscles; they had learnt much about what this part 
or that part of the brain could do; but they did not know that 
one nerve-fibre differed from another in the very essence of its 
work. It was just about the end of the past century, or the 
beginning of the present one, that an English surgeon began to 
ponder over a conception which, however, he did not make 
known until some years later, and which did not gain complete 
demonstration and full acceptance until still more years had 
passed away. It was in 1811, in a tiny pamphlet published 
privately, that Charles Bell put forward his ‘‘ New Idea” that 
the nervous system was constructed on the principle that ‘* the 
nerves are not single nerves possessing various powers, but 
bundles of different nerves, whose filaments are united for the 
convenience of distribution, but which are distinct in office as 
they are in origin from the brain.” 
Our present knowledge of the nervous system is to a large 
extent only an exemplification and expansion of Charles Bell’s 
“* New Idea,” and has its origin in that. 
If we pass from the problems of the living organism viewed 
asa machine to those presented by the varied features of the 
different creatures who have lived or w'o still live on the earth, 
we at once call to mind that the middle years of the present 
century mark an epoch in biologic thought such as never came 
before, for it was then that Charles Darwin gave to the world 
the ‘ Origin of Species.” 
That work, however, with all the far-reaching effects which 
it has had, could have had little or no effect, or, rather, could 
not have come into existence, had not the earlier half of the 
century been in travail preparing for its coming. For the 
germinal idea of Darwin appeals, as to witnesses, to the results 
of two lines of biologic investigation which were almost unknown 
to the men of the eighteenth century. 
To one of these lines I have already referred. Darwin, as we 
know, appealed to the geological record: and we also know 
how that record, imperfect as it was then, and imperfect as it 
must always remain, has since his time yielded the most striking 
proofs of at least one part of his general conception. In 1799 
there was, as we have seen, no geological record at all. 
Of the other line I must say a few words. 
To-day the merest beginner in biologic study, or even that 
exemplar of acquaintance without knowledge, the general 
reader, is aware that every living being, even man himself, 
begins its independent existence as a tiny ball, of which we can, 
even acknowledging to the full the limits of the optical analysis 
at our command, assert with confidence that in structure, using 
that word in its ordinary sense, it is in all cases absolutely 
simple. It is equally well known that the features of form which 
supply the characters of a grown-up living being, all the many 
and varied features of even the most complex organism, are 
reached as the goal of a road, at times a long road, of successive 
changes ; that the life of every being, from the ovum to its full 
estate, is a series of shifting scenes, which come and go, some- 
times changing abruptly, sometimes melting the one into the 
other, like dissolving views, all so ordained that often the final 
shape with which the creature seems to begin, or is said to 
begin, its life in the world is the outcome of many shapes, 
clothed with which it has in turn lived many lives before its 
seeming birth. 
Allor nearly all the exact knowledge of the laboured way in 
which each living creature puts on its proper shape and struc- 
ture is the heritage of the present century. Although the way 
in which the chick is moulded in the egg was not wholly un- 
known even to the ancients, and in later years had been told, 
first in the sixteenth century by Fabricius, then in the seven- 
teenth century in a more clear and striking manner by the great 
Italian naturalist Malpighi, the teaching thus offered had been 
neglected or misinterpreted. At the close of the eighteenth 
century the dominant view was that in the making of a creature 
out of the egg there was no putting on of wholly new parts, no 
epigenesis. It was taught that the entire creature lay hidden in 
the egg, hidden by reason of the very transparency of its sub- 
stance, lay ready-made but folded up, as it were, and that the 
process of development within the egg or within the womb was 
a mere unfolding, a simple evolution. Nor did men shrink 
from accepting the logical outcome of such a view—namely, 
that within the unborn creature itself lay in like manner, hidden 
and folded up, its offspring also, and within that again 
its offspring in turn, after the fashion of a cluster of 
— 
