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Sept. 15, 1870] 
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 par- 
ticular case, before the production of living matter in any other 
way could be admitted by careful reasoners, It will be neces- 
sary 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 Adzogenesis. 
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 ;* 
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 per- 
plexed the Philistines :— 
“* Out of the eater came forth meat, 
And out of the strong came forth sweetness.” 
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 
had lived in these times, would have infallibly caused him to be 
classed among the defenders of ‘‘spontaneous generation.” 
*“Omne yivum 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. t 
ed omnipotente Fattore, non abbia mai pit: prodotto da se medesima né erba 
né albero, né animale alcuno perfetto o imperfetto che ci se fosse ; ¢ che 
tutto quello, che ne’ tempi trapassati é 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 deil’ erbe, e de’ fiori, e dei frutti imputriditi, e corrotti nascere vermi 
infiniti— 
“Nonne vides queecunque 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, ¢ l’erbe, e I'altre cose tutte putrefatte, o putre- 
fattibili non facciano altra parte, né 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 partoritii vermi, 0 
l'uova o I’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.”—Rep1, /sferiense, pp. 14-16. aa 
* “ Molti, e molti altri ancora vi potrei annoverare, se non fossi chiamato 
arispondere alle rampogne di alcuni, che bruscamente mi rammentano cid, 
che si leggenel capitolo quattordicesimo del sacrosanto Libro de’ giudici. 
Pi 
+. .’—Rept, Zc. p. 45. ‘ 
+ The passage (Esperienze, p. 129) is worth quoting in full :—_ tine 
“ Se dovessi palesarvi il mio sentimento crederei che i frutti, i legumi, gli 
alberi ¢ le foglie, in due maniere inverminassero. Una, perché venendo i 
bachi per di fuora, e cercando l’alimento, col rodere ci aprono la strada, ed 
arrivano alla piii interna midolla de’ frutti e de’ legni. L’altra maniera si é, 
che io per me stimerei, che non fosse gran fatto disdicevole il credere, che 
uell’ anima o quella virtii, a quale genera i fiori ed i frutti nelle piante 
viventi, sia quella stessa che generi ancora i bachi diesse piante. E chisa 
orse, che molti fruttidegli alberi non sieno prodotti, non per un fine primario 
€ principale, ma bensi per un uffizio secondario e servile, destinato alla gene- 
razione 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 parra totalmente un 
paradosso ; mentre farete riflessione a quelle tante sorte di galle, di galloz- 
zole, di coccole, di ricci, di calici, di cornetti e di lappole, che son produtte 
dalle querce, dalle farnie, da’ cerri, da’ sugheri, da’ lecci e da altri simili 
alberi da ghianda ; imperciocché in quelle gallozzole, e particolarmente nelle 
pitt 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 
€ principale intenzione della natura @ 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 gallozzolaé finita di maturare e che é@ yenuto il termine destinato 
al suo nascimento, diventa, di verme che era, una mosca. . lo vi 
confesso ingenuamente, che prima d’aver fatte queste mie esperienze intorno 
NATURE 
401 
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 Adiogenesis ; and I shall immediately pro- 
ceed, in the first place, to inquire how far subsequent investiga- 
tion has borne him out in so doing. 
_ But Redi also thought that there were two modes of Biogene- 
sis. By the one method, which is that of common and ordinary 
occurrence, the living parent gives rise to offspring which passes 
through the same cycle of changes as itself—like gives rise to 
like; and this has been termed /omogenesis. By the other 
mode the living parent was supposed to give rise to offspring 
which passed 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 sub- 
stituted for it Xexogenesis, which means the generation of some- 
thing 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, Lyonet, Vallisnieri, Reaumur, and other illus- 
trious investigators of nature of that day, displayed such a com- 
plexity 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 hypo- 
thesis of Abiogenesis began to appear not only untrue, but ab- 
surd; and, in the middle of the eighteenth century, when Needham 
and Buffon took up the question, it was almost universally dis- 
credited.* 
But the skill of the microscope-makers of the eighteenth cen- 
tury soon reached its limit. A microscope magnifying 400 
diameters was a chef d’euvre of the opticians of that day; and 
at the same time, by no means trustworthy. But a magnifying 
power of 400 diameters, even when definition reaches the exqui- 
site perfection of our modern achromatic lenses, hardly suffices 
for the mere discernment of the smallest forms of life. “A speck, 
only y';th of an inch in diameter, has, at 10 inches from the eye, 
the same apparent size as an object yy4yath of an inch in diame- 
ter, when magnified 400 times ; but forms of living matter abound, 
the diameter of which is not more than z5355th of an inch. A 
filtered infusion of hay, allowed to stand for two days, will swarm 
with living things, among which, any which reaches the diameter 
of a human red blood-corpuscle, or about y7;5th of an inch, is 
a giant. It is only by bearing these facts in mind, that we can 
deal fairly with the remarkable statements and speculations put 
forward by Buffon and Needham in the middle of the eighteenth 
century. 
When a portion of any animal or vegetable body is infused in 
water, it gradually softens and disintegrates ; and, as it does so, 
the water is found to swarm with minute active creatures, the so- 
called Infusorial Animalcules, none of which can be seen, except 
by the aid of the microscope ; while a large proportion belong 
to the category of smallest things of which I have spoken, and 
which must have all looked like mere dots and lines under the 
ordinary microscopes of the eighteenth century. 
Led by various theoretical considerations which I cannot now 
discuss, but which looked promising enough in the lights of that 
day, Buffon and Needham doubted the applicability of Redi’s 
hypothesis to the infusorial animalcules, and Needham very 
properly endeavoured to put the question to an experimental test, 
alla generazione degl’ insetti mi dava a credere, o per dir meglio sospettava, 
che forse la gallozzola nascesse, perché arrivando la mosca nel tempo della 
primavera, e facendo una piccolissima fessura ne’ rami pit 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 0 cornetti o calici o coccole, se non in que’ rami, ne’ quali le mosche 
avessero depositate le loro semenze ; € mi dava ad intendere, che le galloz- 
zole fossero una malattia cagionata nelle querce dalle punture delle mosche, 
in quella giusa stessa che dalle punture dialtri animaletti simiglievoli veg- 
giamo crescere de’ tumori ne’ corpi degli animali.” 
* Needham, writing in 1750, says :— 
“Les naturalistes modernes s'accordent unanimement & établir, comme une 
vérité certaine, que toute plante vient de sa sémence spécifique, tout animal 
d'un ceuf ou de quelque chose d’analogue préexistant dans la plante, ou dans 
Yanimal de méme espéce qui I'a produit."—Nouvelles Observations, p. 169. 
“Les naturalistes ont genéralement cru que les animaux microscopique 
étaient engendrés par des ceufs transportés dans I'air, ou déposés dans des 
eaux dormantes par des insectes volans,”—J¢id. p. 176. 
