Discourses - Thomas H. Huxley
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All that literature has to bestow may be obtained by reading and by
practical exercise in writing and in speaking; but I do not exaggerate
when I say, that none of the best gifts of science are to be won by these
means. On the contrary, the great benefit which a scientific education
bestows, whether is training or as knowledge, is dependent upon the
extent to which the mind of the student is brought into immediate contact
with facts--upon the degree to which he learns the habit of appealing
directly to Nature, and of acquiring through his senses concrete images
of those properties of things, which are, and always will be, but
approximatively expressed in human language. Our way of looking at
Nature, and of speaking about her, varies from year to year; but a fact
once seen, a relation of cause and effect, once demonstratively
apprehended, are possessions which neither change nor pass away, but, on
the contrary, form fixed centres, about which other truths aggregate by
natural affinity.
Therefore, the great business of the scientific teacher is, to imprint
the fundamental, irrefragable facts of his science, not only by words
upon the mind, but by sensible impressions upon the eye, and ear, and
touch of the student, in so complete a manner, that every term used, or
law enunciated, should afterwards call up vivid images of the particular
structural, or other, facts which furnished the demonstration of the law,
or the illustration of the term.
Now this important operation can only be achieved by constant
demonstration, which may take place to a certain imperfect extent during
a lecture, but which ought also to be carried on independently, and which
should be addressed to each individual student, the teacher endeavouring,
not so much to show a thing to the learner, as to make him see it for
himself.
I am well aware that there are great practical difficulties in the way of
effectual zoological demonstrations. The dissection of animals is not
altogether pleasant, and requires much time; nor is it easy to secure an
adequate supply of the needful specimens. The botanist has here a great
advantage; his specimens are easily obtained, are clean and wholesome,
and can be dissected in a private house as well as anywhere else; and
hence, I believe, the fact, that botany is so much more readily and
better taught than its sister science. But, be it difficult or be it
easy, if zoological science is to be properly studied, demonstration,
and, consequently, dissection, must be had. Without it, no man can have a
really sound knowledge of animal organisation.
A good deal may be done, however, without actual dissection on the
student's part, by demonstration upon specimens and preparations; and in
all probability it would not be very difficult, were the demand
sufficient, to organise collections of such objects, sufficient for all
the purposes of elementary teaching, at a comparatively cheap rate. Even
without these, much might be effected, if the zoological collections,
which are open to the public, were arranged according to what has been
termed the "typical principle"; that is to say, if the specimens exposed
to public view were so selected that the public could learn something
from them, instead of being, as at present, merely confused by their
multiplicity. For example, the grand ornithological gallery at the
British Museum contains between two and three thousand species of birds,
and sometimes five or six specimens of a species. They are very pretty to
look at, and some of the cases are, indeed, splendid; but I will
undertake to say, that no man but a professed ornithologist has ever
gathered much information from the collection. Certainly, no one of the
tens of thousands of the general public who have walked through that
gallery ever knew more about the essential peculiarities of birds when he
left the gallery than when he entered it. But if, somewhere in that vast
hall, there were a few preparations, exemplifying the leading structural
peculiarities and the mode of development of a common fowl; if the types
of the genera, the leading modifications in the skeleton, in the plumage
at various ages, in the mode of nidification, and the like, among birds,
were displayed; and if the other specimens were put away in a place where
the men of science, to whom they are alone useful, could have free access
to them, I can conceive that this collection might become a great
instrument of scientific education.
The last implement of the teacher to which I have adverted is
examination--a means of education now so thoroughly understood that I
need hardly enlarge upon it. I hold that both written and oral
examinations are indispensable, and, by requiring the description of
specimens, they may be made to supplement demonstration.
Such is the fullest reply the time at my disposal will allow me to give
to the question--how may a knowledge of zoology be best acquired and
communicated?
But there is a previous question which may be moved, and which, in fact,
I know many are inclined to move. It is the question, why should teachers
be encouraged to acquire a knowledge of this, or any other branch of
physical science? What is the use, it is said, of attempting to make
physical science a branch of primary education? Is it not probable that
teachers, in pursuing such studies, will be led astray from the
acquirement of more important but less attractive knowledge? And, even if
they can learn something of science without prejudice to their
usefulness, what is the good of their attempting to instil that knowledge
into boys whose real business is the acquisition of reading, writing, and
arithmetic?
These questions are, and will be, very commonly asked, for they arise
from that profound ignorance of the value and true position of physical
science, which infests the minds of the most highly educated and
intelligent classes of the community. But if I did not feel well assured
that they are capable of being easily and satisfactorily answered; that
they have been answered over and over again; and that the time will come
when men of liberal education will blush to raise such questions--I
should be ashamed of my position here to-night. Without doubt, it is your
great and very important function to carry out elementary education;
without question, anything that should interfere with the faithful
fulfilment of that duty on your part would be a great evil; and if I
thought that your acquirement of the elements of physical science, and
your communication of those elements to your pupils, involved any sort of
interference with your proper duties, I should be the first person to
protest against your being encouraged to do anything of the kind.
But is it true that the acquisition of such a knowledge of science as is
proposed, and the communication of that knowledge, are calculated to
weaken your usefulness? Or may I not rather ask, is it possible for you
to discharge your functions properly without these aids?
What is the purpose of primary intellectual education? I apprehend that
its first object is to train the young in the use of those tools
wherewith men extract knowledge from the ever-shifting succession of
phenomena which pass before their eyes; and that its second object is to
inform them of the fundamental laws which have been found by experience
to govern the course of things, so that they may not be turned out into
the world naked, defenceless, and a prey to the events they might
control.
A boy is taught to read his own and other languages, in order that he may
have access to infinitely wider stores of knowledge than could ever be
opened to him by oral intercourse with his fellow men; he learns to
write, that his means of communication with the rest of mankind may be
indefinitely enlarged, and that he may record and store up the knowledge
he acquires. He is taught elementary mathematics, that he may understand
all those relations of number and form, upon which the transactions of
men, associated in complicated societies, are built, and that he may have
some practice in deductive reasoning.
All these operations of reading, writing, and ciphering, are intellectual
tools, whose use should, before all things, be learned, and learned
thoroughly; so that the youth may be enabled to make his life that which
it ought to be, a continual progress in learning and in wisdom.
But, in addition, primary education endeavours to fit a boy out with a
certain equipment of positive knowledge. He is taught the great laws of
morality; the religion of his sect; so much history and geography as will
tell him where the great countries of the world are, what they are, and
how they have become what they are.
Without doubt all these are most fitting and excellent things to teach a
boy; I should be very sorry to omit any of them from any scheme of
primary intellectual education. The system is excellent, so far as it
goes.
But if I regard it closely, a curious reflection arises. I suppose that,
fifteen hundred years ago, the child of any well-to-do Roman citizen was
taught just these same things; reading and writing in his own, and,
perhaps, the Greek tongue; the elements of mathematics; and the religion,
morality, history, and geography current in his time. Furthermore, I do
not think I err in affirming, that, if such a Christian Roman boy, who
had finished his education, could be transplanted into one of our public
schools, and pass through its course of instruction, he would not meet
with a single unfamiliar line of thought; amidst all the new facts he
would have to learn, not one would suggest a different mode of regarding
the universe from that current in his own time.
And yet surely there is some great difference between the civilisation of
the fourth century and that of the nineteenth, and still more between the
intellectual habits and tone of thought of that day and this?
And what has made this difference? I answer fearlessly--The prodigious
development of physical science within the last two centuries.
Modern civilisation rests upon physical science; take away her gifts to
our own country, and our position among the leading nations of the world
is gone to-morrow; for it is physical science only that makes
intelligence and moral energy stronger than brute force.
The whole of modern thought is steeped in science; it has made its way
into the works of our best poets, and even the mere man of letters, who
affects to ignore and despise science, is unconsciously impregnated with
her spirit, and indebted for his best products to her methods. I believe
that the greatest intellectual revolution mankind has yet seen is now
slowly taking place by her agency. She is teaching the world that the
ultimate court of appeal is observation and experiment, and not
authority; she is teaching it to estimate the value of evidence; she is
creating a firm and living faith in the existence of immutable moral and
physical laws, perfect obedience to which is the highest possible aim of
an intelligent being.
But of all this your old stereotyped system of education takes no note.
Physical science, its methods, its problems, and its difficulties, will
meet the poorest boy at every turn, and yet we educate him in such a
manner that he shall enter the world as ignorant of the existence of the
methods and facts of science as the day he was born. The modern world is
full of artillery; and we turn out our children to do battle in it,
equipped with the shield and sword of an ancient gladiator.
Posterity will cry shame on us if we do not remedy this deplorable state
of things. Nay, if we live twenty years longer, our own consciences will
cry shame on us.
It is my firm conviction that the only way to remedy it is to make the
elements of physical science an integral part of primary education. I
have endeavoured to show you how that may be done for that branch of
science which it is my business to pursue; and I can but add, that I
should look upon the day when every schoolmaster throughout this land was
a centre of genuine, however rudimentary, scientific knowledge, as an
epoch in the history of the country.
But let me entreat you to remember my last words. Addressing myself to
you, as teachers, I would say, mere book learning in physical science is
a sham and a delusion--what you teach, unless you wish to be impostors,
that you must first know; and real knowledge in science means personal
acquaintance with the facts, be they few or many.[2]
[Footnote 2: It has been suggested to me that these words may be taken to
imply a discouragement on my part of any sort of scientific instruction
which does not give an acquaintance with the facts at first hand. But
this is not my meaning. The ideal of scientific teaching is, no doubt, a
system by which the scholar sees every fact for himself, and the teacher
supplies only the explanations. Circumstances, however, do not often
allow of the attainment of that ideal, and we must put up with the next
best system--one in which the scholar takes a good deal on trust from a
teacher, who, knowing the facts by his own knowledge, can describe them
with so much vividness as to enable his audience to form competent ideas
concerning them. The system which I repudiate is that which allows
teachers who have not come into direct contact with the leading facts of
a science to pass their second-hand information on. The scientific virus,
like vaccine lymph, if passed through too long a succession of organisms,
will lose all its effect in protecting the young against the intellectual
epidemics to which they are exposed.
[The remarks on p. 222 applied to the Natural History Collection of the
British Museum in 1861. The visitor to the Natural History Museum in 1894
need go no further than the Great Hall to see the realisation of my hopes
by the present Director.]]
VIII
BIOGENESIS AND ABIOGENESIS
(THE PRESIDENTIAL ADDRESS TO THE BRITISH ASSOCIATION FOR THE ADVANCEMENT
OF SCIENCE FOR 1870)
It has long been the custom for the newly installed President of the
British Association for the Advancement of Science to take advantage of
the elevation of the position in which the suffrages of his colleagues
had, for the time, placed him, and, casting his eyes around the horizon
of the scientific world, to report to them what could be seen from his
watch-tower; in what directions the multitudinous divisions of the noble
army of the improvers of natural knowledge were marching; what important
strongholds of the great enemy of us all, ignorance, had been recently
captured; and, also, with due impartiality, to mark where the advanced
posts of science had been driven in, or a long-continued siege had made
no progress.
I propose to endeavour to follow this ancient precedent, in a manner
suited to the limitations of my knowledge and of my capacity. I shall not
presume to attempt a panoramic survey of the world of science, nor even
to give a sketch of what is doing in the one great province of biology,
with some portions of which my ordinary occupations render me familiar.
But I shall endeavour to put before you the history of the rise and
progress of a single biological doctrine; and I shall try to give some
notion of the fruits, both intellectual and practical, which we owe,
directly or indirectly, to the working out, by seven generations of
patient and laborious investigators, of the thought which arose, more
than two centuries ago, in the mind of a sagacious and observant Italian
naturalist.
It is a matter of everyday experience that it is difficult to prevent
many articles of food from becoming covered with mould; that fruit, sound
enough to all appearance, often contains grubs at the core; that meat,
left to itself in the air, is apt to putrefy and swarm with maggots. Even
ordinary water, if allowed to stand in an open vessel, sooner or later
becomes turbid and full of living matter.
The philosophers of antiquity, interrogated as to the cause of these
phenomena, were provided with a ready and a plausible answer. It did not
enter their minds even to doubt that these low forms of life were
generated in the matters in which they made their appearance. Lucretius,
who had drunk deeper of the scientific spirit than any poet of ancient or
modern times except Goethe, intends to speak as a philosopher, rather
than as a poet, when he writes that "with good reason the earth has
gotten the name of mother, since all things are produced out of the
earth. And many living creatures, even now, spring out of the earth,
taking form by the rains and the heat of the sun."[1] The axiom of
ancient science, "that the corruption of one thing is the birth of
another," had its popular embodiment in the notion that a seed dies
before the young plant springs from it; a belief so widespread and so
fixed, that Saint Paul appeals to it in one of the most splendid
outbursts of his fervid eloquence:--
"Thou fool, that which thou sowest is not quickened, except it die."[2]
[Footnote 1: It is thus that Mr. Munro renders
"Linquitur, ut merito maternum nomen adepta
Terra sit, e terra quoniam sunt cuncta creata.
Multaque nunc etiam exsistant animalia terris
Imbribus et calido solis concreta vapore."
_De Rerum Natura_, lib. v. 793-796.
But would not the meaning of the last line be better rendered "Developed
in rain-water and in the warm vapours raised by the sun"?]
[Footnote 2: 1 Corinthians xv. 36.]
The proposition that life may, and does, proceed from that which has no
life, then, was held alike by the philosophers, the poets, and the
people, of the most enlightened nations, eighteen hundred years ago; and
it remained the accepted doctrine of learned and unlearned Europe,
through the Middle Ages, down even to the seventeenth century.
It is commonly counted among the many merits of our great countryman,
Harvey, that he was the first to declare the opposition of fact to
venerable authority in this, as in other matters; but I can discover no
justification for this widespread notion. After careful search through
the "Exercitationes de Generatione," the most that appears clear to me
is, that Harvey believed all animals and plants to spring from what he
terms a "_primordium vegetale_," a phrase which may nowadays be rendered
"a vegetative germ"; and this, he says, is _"oviforme_," or "egg-like";
not, he is careful to add, that it necessarily has the shape of an egg,
but because it has the constitution and nature of one. That this
"_primordium oviforme_" must needs, in all cases, proceed from a living
parent is nowhere expressly maintained by Harvey, though such an opinion
may be thought to be implied in one or two passages; while, on the other
hand, he does, more than once, use language which is consistent only with
a full belief in spontaneous or equivocal generation.[3] In fact, the
main concern of Harvey's wonderful little treatise is not with
generation, in the physiological sense, at all, but with development; and
his great object is the establishment of the doctrine of epigenesis.
[Footnote 3: See the following passage in Exercitatio I.:--"Item _sponte
nascentia_ dicuntur; non quod ex _putredine_ oriunda sint, sed quod casu,
naturae sponte, et aequivoca (ut aiunt) generatione, a parentibus sui
dissimilibus proveniant." Again, in _De Uteri Membranis:_--"In cunctorum
viventium generatione (sicut diximus) hoc solenne est, ut ortum ducunt a
_primordio_ aliquo, quod tum materiam tum elficiendi potestatem in se
habet: sitque, adeo id, ex quo et a quo quicquid nascitur, ortum suum
ducat. Tale primordium in animalibus (_sive ab aliis generantibus
proveniant, sive sponte, aut ex putredine nascentur_) est humor in
tunica, aliquaaut putami ne conclusus." Compare also what Redi has to say
respecting Harvey's opinions, _Esperienze_, p. 11.]
The first distinct enunciation of the hypothesis that all living matter
has sprung from pre-existing living matter, came from a contemporary,
though a junior, of Harvey, a native of that country, fertile in men
great in all departments of human activity, which was to intellectual
Europe, in the sixteenth and seventeenth centuries, what Germany is in
the nineteenth. It was in Italy, and from Italian teachers, that Harvey
received the most important part of his scientific education. And it was
a student trained in the same schools, Francesco Redi--a man of the
widest knowledge and most versatile abilities, distinguished alike as
scholar, poet, physician, and naturalist--who, just two hundred and two
years ago, published his "Esperienze intorno alla Generazione degl'
Insetti," and gave to the world the idea, the growth of which it is my
purpose to trace. Redi's book went through five editions in twenty years;
and the extreme simplicity of his experiments, and the clearness of his
arguments, gained for his views, and for their consequences, almost
universal acceptance.
Redi did not trouble himself much with speculative considerations, but
attacked particular cases of what was supposed to be "spontaneous
generation" experimentally. Here are dead animals, or pieces of meat,
says he; I expose them to the air in hot weather, and in a few days they
swarm with maggots. You tell me that these are generated in the dead
flesh; but if I put similar bodies, while quite fresh, into a jar, and
tie some fine gauze over the top of the jar, not a maggot makes its
appearance, while the dead substances, nevertheless, putrefy just in the
same way as before. It is obvious, therefore, that the maggots are not
generated by the corruption of the meat; and that the cause of their
formation must be a something which is kept away by gauze. But gauze will
not keep away aeriform bodies, or fluids. This something must, therefore,
exist in the form of solid particles too big to get through the gauze.
Nor is one long left in doubt what these solid particles are; for the
blowflies, attracted by the odour of the meat, swarm round the vessel,
and, urged by a powerful but in this case misleading instinct, lay eggs
out of which maggots are immediately hatched, upon the gauze. The
conclusion, therefore, is unavoidable; the maggots are not generated by
the meat, but the eggs which give rise to them are brought through the
air by the flies.
These experiments seem almost childishly simple, and one wonders how it
was that no one ever thought of them before. Simple as they are, however,
they are worthy of the most careful study, for every piece of
experimental work since done, in regard to this subject, has been shaped
upon the model furnished by the Italian philosopher. As the results of
his experiments were the same, however varied the nature of the materials
he used, it is not wonderful that there arose in Redi's mind a
presumption, that, in all such cases of the seeming production of life
from dead matter, the real explanation was the introduction of living
germs from without into that dead matter.[4] And thus the hypothesis that
living matter always arises by the agency of pre-existing living matter,
took definite shape; and had, henceforward, a right to be considered and
a claim to be refuted, in each particular case, before the production of
living matter in any other way could be admitted by careful reasoners. It
will be necessary for me to refer to this hypothesis so frequently, that,
to save circumlocution, I shall call it the hypothesis of _Biogenesis_;
and I shall term the contrary doctrine--that living matter may be
produced by not living matter--the hypothesis of _Abiogenesis_.
[Footnote 4: "Pure contentandomi sempre in questa ed in ciascuna altro
cosa, da ciascuno piu savio, la dove io difettuosamente parlassi, esser
corretto; non tacero, che per molte osservazioni molti volti da me fatte,
mi sento inclinato a credere che la terra, da quelle prime piante, e da
quei primi animali in poi, che ella nei primi giorni del mondo produsse
per comandemento del sovrano ed omnipotente Fattore, non abbia mai piu
prodotto da se medesima ne erba ne albero, ne animale alcuno perfetto o
imperfetto che ei se fosse; e che tutto quello, che ne' tempi trapassati
e nato e che ora nascere in lei, o da lei veggiamo, venga tutto dalla
semenza reale e vera delle piante, e degli animali stessi, i quali col
mezzo del proprio seme la loro spezie conservano. E se bene tutto giorno
scorghiamo da' cadaveri degli animali, e da tutte quante le maniere dell'
erbe, e de' fiori, e dei frutti imputriditi, e corrotti nascere vermi
infiniti--
'Nonne vides quaecunque mora, fluidoque calore
Corpora tabescunt in parva animalia verti'--
Io mi sento, dico, inclinato, a credere che tutti quei vermi si generino
dal seme paterno; e che le carni, e l' erbe, e l' altre cose tutte
putrefatte, o putrefattibili non facciano altra parte, ne abbiano altro
ufizio nella generazione degl' insetti, se non d'apprestare un luogo o un
nido proporzionato, in cui dagli animali nel tempo della figliatura sieno
portati, e partoriti i vermi, o l' uova o l' altre semenze dei vermi, i
quali tosto che nati sono, trovano in esso nido un sufficiente alimento
abilissimo per nutricarsi: e se in quello non son portate dalle madri
queste suddette semenze, niente mai, e replicatamente niente, vi s'
ingegneri e nasca."--REDI, _Esperienze_, pp. 14-16.]