Discourses: Biological & Geological Part 12

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 s.h.i.+eld 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. Circ.u.mstances, 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 pa.s.s their second-hand information on. The scientific virus, like vaccine lymph, if pa.s.sed 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 a.s.sOCIATION FOR THE ADVANCEMENT OF SCIENCE FOR 1870)

It has long been the custom for the newly installed President of the British a.s.sociation 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 mult.i.tudinous divisions of the n.o.ble 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 const.i.tution 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 pa.s.sages; 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 pa.s.sage in Exercitatio I.:--"Item _sponte nascentia_ dic.u.n.tur; 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 duc.u.n.t 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 circ.u.mlocution, 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 parla.s.si, 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 trapa.s.sati e nato e che ora nascere in lei, o da lei veggiamo, venga tutto dalla s.e.m.e.nza 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 tabesc.u.n.t 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 s.e.m.e.nze 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 s.e.m.e.nze, 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 ci, 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 cla.s.sed 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 antic.i.p.ated 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 pa.s.sage (_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 invermina.s.sero. Una, perche venendo i bachi per di fuora, e cercando l' alimento, col rodere ci ap.r.o.no la strada, ed arrivano alla piu interna midolla de' frutti e de'

legni. L'altra maniera si e, che io per me stimerei, che non fosse gran fatto disdicevole il credere, che quell' anima o quella virtu, la quale genera i fiori ed i frutti nelle piante viventi, sia quella stessa che generi ancora i bachi di esse piante. E chi sa, forse, che molti frutti degli alberi non sieno prodotti, non per un fine primario e princ.i.p.ale, 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 G.o.dere il sole.

"Io m' immagino, che questo mio pensiero non vi parra 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; imperciocche in quello gallozzole, e particolarmente nelle piu 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 princ.i.p.ale intenzione della natura e 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 e finita di maturare e che e 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, perche arrivando la mosca nel tempo della primavera, e facendo una piccolissima fessura ne' rami piu teneri della quercia, in quella fessura nascondesse uno de suoi semi, il quale fosse cagione che sboccia.s.se 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 s.e.m.e.nze; 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.

But Redi also thought that there were two modes of Biogenesis. By the one method, which is that of common and ordinary occurrence, the living parent gives rise to offspring which pa.s.ses through the same cycle of changes as itself--like gives rise to like; and this has been termed _h.o.m.ogenesis_. By the other mode, the living parent was supposed to give rise to offspring which pa.s.sed through a totally different series of states from those exhibited by the parent, and did not return into the cycle of the parent; this is what ought to be called _Heterogenesis_, the offspring being altogether, and permanently, unlike the parent. The term Heterogenesis, however, has unfortunately been used in a different sense, and M. Milne-Edwards has therefore subst.i.tuted for it _Xenogenesis_, which means the generation of something foreign. After discussing Redi's hypothesis of universal Biogenesis, then, I shall go on to ask how far the growth of science justifies his other hypothesis of Xenogenesis.

The progress of the hypothesis of Biogenesis was triumphant and unchecked for nearly a century. The application of the microscope to anatomy in the hands of Grew, Leeuwenhoek, Swammerdam, Lyonnet, Vallisnieri, Reaurnur, and other ill.u.s.trious investigators of nature of that day, displayed such a complexity of organisation in the lowest and minutest forms, and everywhere revealed such a prodigality of provision for their multiplication by germs of one sort or another, that the hypothesis of Abiogenesis began to appear not only untrue, but absurd; and, in the middle of the eighteenth century, when Needham and Buffon took up the question, it was almost universally discredited.[7]

[Footnote 7: Needham, writing in 1750, says:--

"Les naturalistes modernes s'accordent unaninement a etablir, comme une verite certaine, que toute plante vient do sa s.e.m.e.nce specifique, tout animal d'un oeuf ou de quelque chose d'a.n.a.logue preexistant dans la plante, ou dans l'animal de meme espece qui l'a produit."--_Nouvelles Observations_, p. 169.