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 aequivocâ (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
tunicâ, aliquâaut 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 aëriform 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 più savio, là 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 più
prodotto da se medesima nè erba nè albero, nè animale alcuno perfetto o
imperfetto che ei se fosse; e che tutto quello, che ne' tempi trapassati
è 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, nè 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.]
In the seventeenth century, as I have said, the latter was the dominant
view, sanctioned alike by antiquity and by authority; and it is
interesting to observe that Redi did not escape the customary tax upon a
discoverer of having to defend himself against the charge of impugning
the authority of the Scriptures;[5] for his adversaries declared that the
generation of bees from the carcase of a dead lion is affirmed, in the
Book of Judges, to have been the origin of the famous riddle with which
Samson perplexed the Philistines:--
Out of the eater came forth meat,
And out of the strong came forth sweetness.
[Footnote 5: "Molti, e molti altri ancora vi potrei annoverare, se non
fossi chiamato a rispondere alle rampogne di alcuni, che bruscamente mi
rammentano ciò, che si legge nel capitolo quattordicesimo del sacrosanto
Libro de' giudici ... "--REDI, _loc. cit._ p. 45.]
Against all odds, however, Redi, strong with the strength of demonstrable
fact, did splendid battle for Biogenesis; but it is remarkable that he
held the doctrine in a sense which, if he lead lived in these times,
would have infallibly caused him to be classed among the defenders of
"spontaneous generation." "Omne vivum ex vivo," "no life without
antecedent life," aphoristically sums up Redi's doctrine; but he went no
further. It is most remarkable evidence of the philosophic caution and
impartiality of his mind, that although he had speculatively anticipated
the manner in which grubs really are deposited in fruits and in the galls
of plants, he deliberately admits that the evidence is insufficient to
bear him out; and he therefore prefers the supposition that they are
generated by a modification of the living substance of the plants
themselves. Indeed, he regards these vegetable growths as organs, by
means of which the plant gives rise to an animal, and looks upon this
production of specific animals as the final cause of the galls and of, at
any rate, some fruits. And he proposes to explain the occurrence of
parasites within the animal body in the same way.[6]
[Footnote 6: The passage (_Esperienze_, p. 129) is worth quoting in
full:--
"Se dovessi palesarvi il mio sentimento crederei che i frutti, i legumi,
gli alberi e le foglie, in due maniere inverminassero. Una, perchè
venendo i bachi per dí fuora, e cercando l' alimento, col rodere ci
aprono la strada, ed arrivano alla più interna midolla de' frutti e de'
legni. L'altra maniera si è, che io per me stimerei, che non fosse gran
fatto disdicevole il credere, che quell' anima o quella virtù, la quale
genera i fiori ed i frutti nelle piante viventi, sia quella stessa che
generi ancora i bachi di esse piante. E chi sà, forse, che molti frutti
degli alberi non sieno prodotti, non per un fine primario e principale,
ma bensi per un uffizio secondario e servile, destinato alla generazione
di que' vermi, servendo a loro in vece di matrice, in cui dimorino un
prefisso e determinato tempo; il quale arrivato escan fuora a godere il
sole.
"Io m' immagino, che questo mio pensiero non vi parrà totalmento un
paradosso; mentro farete riflessione a quelle tanto sorte di galle, di
gallozzole, di coccole, di ricci, di calici, di cornetti ed i lappole,
che son produtte dalle quercel, dalle farnie, da' cerri, da' sugheri, da'
leeci e da altri simili alberi de ghianda; imperciocchè in quello
gallozzole, e particolarmente nelle più grosse, che si chiamano coronati,
ne' ricci capelluti, che ciuffoli da' nostri contadini son detti; nei
ricci legnosi del cerro, ne' ricci stellati della quercia, nelle galluzze
della foglia del leccio si vede evidentissimamente, che la prima e
principale intenzione della natura è formare dentro di quelle un animale
volante; vedendosi nel centro della gallozzola un uovo, che col crescere
e col maturarsi di essa gallozzola va crescendo e maturando anch' egli, e
cresce altresi a suo tempo quel verme, che nell' uovo si racchiude; il
qual verme, quando la gallozzola è finita di maturare e che è venuto il
termine destinato al suo nascimento, diventa, di verme che era, una
mosca.... Io vi confesso ingenuamente, che prima d'aver fatte queste mie
esperienze intorno alla generazione degl' insetti mi dava a credere, o
per dir meglio sospettava, che forse la gallozzola nascesse, perchè
arrivando la mosca nel tempo della primavera, e facendo una piccolissima
fessura ne' rami più teneri della quercia, in quella fessura nascondesse
uno de suoi semi, il quale fosse cagione che sbocciasse fuora la
gallozzola; e che mai non si vedessero galle o gallozzole o ricci o
cornetti o calici o coccole, se non in que' rami, ne' quali le mosche
avessero depositate le loro semenze; e mi dava ad intendere, che le
gallozzole fossero una malattia cagionata nelle querce dalle punture
delle mosche, in quella giusa stessa che dalle punture d'altri animaletti
simiglievoli veggiamo crescere de' tumori ne' corpi degli animali."]
It is of great importance to apprehend Redi's position rightly; for the
lines of thought he laid down for us are those upon which naturalists
have been working ever since. Clearly, he held _Biogenesis_ as against
_Abiogenesis;_ and I shall immediately proceed, in the first place, to
inquire how far subsequent investigation has borne him out in so doing.