COMPARISON OF MY OBSERVATIONS WITH THOSE OF LEEUWENHOEK.
Although I made the preceding experiments with all the circumspection
possible; and although I repeated them a number of times, I am
persuaded that many things escaped my notice; I have only related what
I saw, and what all the world may see, with a little art and much
practice. In order to be free from prejudices, I endeavoured to forget
what other naturalists asserted to have seen, conceiving that by so
doing, I should be more certain of only seeing in fact what really
appeared; and it was not till after I had digested my observations,
that I compared them with those of Leeuwenhoek, &c. I by no means
pretend to have greater abilities in microscopical observations than
that great naturalist, who passed more than sixty years in making
various experiments.
Notwithstanding the authority his observations may justly claim, it
is surely permitted to examine and compare others with them. Truth
can only be gained by such examinations, and errors discovered,
particularly as we do it without any partiality, and in the sole view
of establishing something fixed and certain on the nature of those
moving bodies seen in the seminal liquors.
In November 1677, Leeuwenhoek, who had already communicated to the
Royal Society of London many microscopical observations on the optic
nerve, the blood, the juice of the plants, the texture of trees,
rain-water, &c. addressed to Lord Brouncker, President of the Society,
in the following words: "Postquam Exc.[S] &c. Dominus Professor
Cranen me visitatione sua sæpius honorarat, litteris rogavis, Domino
Ham concrato suo, quasdam observationum mearum, videndas darem. Hic
dominus Ham me secundo invisens, secum in laguncula, vitrea semen
viri, gonorrhæa laborantis, sponte destillatum, attulit, dicens, se
post paucissimas temporis minutias (cum materia ilia jam in tantum
esset resoluta ut fistulæ vitreæ immitti posset) animalcula viva in
eo observasse, quæ caudam & ultra 24 horas non viventia judicabat;
idem referebat se animalcula observasse mortua post sumptam ab ægroto
therebintinam. Materiam prædicatam fistulæ vitreæ immissam, præsente
Domino Ham, observavi, quasdamque in ea creaturas viventes, at post
decursum 2 aut 3 horarum eamdem solus materiam observans, mortuas vidi.
[S] See Phil. Trans. No. 141, page 1041.
"Eamdem materiam (semen virile) non ægroti alicujus, non diuturna
conservatione corruptam, vel post aliquot momenta fluidiorem factam,
sed sani viri statim post ejectionem, ne interlabentibus quidem sex
arteriæ pulsibus, sæpiuscule observavi, tantamque in ea viventium
animalculorum multitudinem vidi, ut interdum plura quam 1000 in
magnitudine arenæ sese moverent; non in toto semine, sed in materia
fluida crassiori adhærente, ingentem illam animalculorum multitudinem
observavi; in crassiori vero seminis materia quasi sine motu jacebant,
quod inde provenire mihi imaginabar, quod materia illa crassa ex tam
variis cohæreat partibus, ut animalcula in ea se movere nequirent;
minora globulis sanguini ruborem adferentibus hæc animalcula erant, ut
judicem, millena millia arenam grandiorem magnitudine non æquatura.
Corpora corum rotunda, anteriora obtusa, posteriora ferme in aculeum
desinentia habebant; cauda tenui longitudine corpus quinquies sexiesve
excedente, & pellucida crassitiem vero ad 25 partem corporis habente
prædita erant, adeo ut ea quoad figuram cum cyclaminis minoribus,
longam caudam habentibus, optime, comparare queam; motu caudæ
serpentino, aut ut anguillæ in aqua natantis progrediebantur; in
materia vero aliquantulum crassiori caudam octies deciesve quidem
evibrabant antequam latitudinem capilli procedebant. Interdum mihi
imaginabar me internoscere posse adhuc varias in corpore horum
animalculorum partes, quia vero continuo eas videre nequibam, de iis
tacebo. His animalculis minora adhuc animalcula, quibus non nisi
globuli figuram attribuere possum, permissa erant.
"Memini me ante tres aut quatuor annos, rogatu Domini Oldenburg, B. M.
semen virile observasse, & prædicta animalia pro globulis habuisse;
sed quia fastidiebam ab ulteriori inquisitione, & magis quidem a
descriptione, tunc temporis eam omisi. Jam quoad partes ipsas, ex
quibus crassam seminis materiam, quoad majorem sui partem consistere
sæpius cum admiratione observavi, ea sunt tam varia ac multa vasa, imo
in tanta multitudine hæc vasa vidi, ut credam me in unica seminis gutta
plura observasse quam anatomico per integrum diem subjectum aliquod
secanti occurrant. Quibus visis, firmiter credebam nulla in corpore
humano jam formato esse vasa, quæ in semine virili bene constituto non
reperiantur. Cum materia hæc per momenta quædam aëri fuisset exposita,
prædicta vasorum multitudo in aquosam magnis oleaginosis globulis
permistam materiam mutabatur, &c."
The Secretary of the Royal Society, in answer to this letter, says,
that it would be proper to make the like experiments on the seed of
other animals, as dogs, horses, &c. not only to form a better judgment
on the first discovery, but to know the differences which might be
found in the number, and the figure of those animalcules. And with
relation to the vessels of the thickest part of the seminal liquors,
he greatly doubts they were only filaments without any organization,
"quæ tibi videbatur vasorum congeries, fortassis seminis sunt
quædam filamenta, haud organice constructa, sed dum permearunt vasa
generationi inservientia in istiusmodi figuram elongata. Non dissimili
modo ac sæpius notatus sum salivam crassiorem ex glandularum faucium
foraminibus editam quasi e convolutis fibrilis constantem."[T]
[T] See the Secretary's answer to Leeuwenhoek's Letter in the Phil.
Trans. No. 141, page 1043.
Leeuwenhoek answered him on the 18th of March, 1678, in the following
words: "Si quando canes coeunt marem a foemina statim seponas materia
quædam tenuis & aquosa (lympha scilicet spermatica) e pene solet
paulatim exstillare; hanc materiam numerosissimis animalculis repletam
aliquoties vidi, eorum magnitudine quæ in semine virili conspiciuntur,
quibus particulæ globulares aliquot quinquagies majores permiscebantur.
"Quod ad vasorem in crassiori seminis virilis portione spectabilium
observationem attinet, denuo non semel iteratam, saltem mihimetipsi
comprobasse videor; meque omnino persuasum habeo, cuniculi, canis,
felis, arterias venasve fuisse a peritissimo anatomico haud unquam
magis perspicue observatas, quam mihi rasa in semine virili, ope
perspicilli, in confectum venere.
"Cum mihi prædicta vasa primum innotuere, statim etiam pituitam, tum
& salivam perspicillo applicavi; verum his minime existentia animalia
frustra quæsivi.
"A cuniculorum coitu lymphæ spermaticæ guttulam, unam et alteram,
e femella exstillantem, examini subjeci, ubi animalia prædictorum
similia, sed longe pauciora, comparuere. Globuli item quam plurimi,
plerique magnitudine animalium, iisdem permisti sunt.
"Horum animalium aliquot etiam delineationes transmisi, figura _a_
(_plate 3._) exprimit corum aliquot vivum (in semine cuniculi arbitror)
eaque forma qua videbatur, dum aspicientem me versus tendit. A B C,
capitulum cum trunco indicant; C D, ejusdem caudam, quam pariter ut
suam anguilla inter natandum vibrat. Horum millena millia, quantum
conjectare est, arenulæ majoris molem vix superant, (_fig. b, c, d,_)
sunt ejusdem generis animalia, sed jam mortua.
[Illustration: _PLATE. III._]
"(_Fig. e._) Delineatur vivum animalculum, quemadmodum in semine canino
sese aliquoties mihi attentius intuenti exhibuit. E F G, caput cum
trunco indigitant, G H ejusdem caudam, (_fig. f, g, h,_) alia sunt in
semine canino quæ motu & vita privantur, qualium etiam vivorum numerum
adeo ingentem vidi, ut judicarem portionem lymphæ spermaticæ arenulæ
mediocri respondentem, eorum ut minimum decena millia continere."
By another letter written to the Royal Society, the 31st of May,
1678, Leeuwenhoek adds, "Seminis canini tantillum microscopio
applicatum iterum contemplatus sum, in eoque antea descripta animalia
numerosissime conspexi. Aqua pluvialis pari quantitate adjecta, iisdem
confestim mortem accersit. Ejusdem seminis canini portiuncula in vitreo
tubulo unciæ partem duodecimalem crasso servata, sex & triginta horarum
spatio contenta animalia vita destitua pleraque, reliqua moribunda
videbantur.
"Quo de vasorum in semine genitali existentia magis constaret,
delineationem eorum aliqualem mitto, ut in figura ABCDE, (_fig. i._)
quibus literis circumscriptum spatium arenulam mediocrem vix superat."
I have copied these first remarks of Leeuwenhoek from the Philosophical
Transactions, because, in matters of this kind, observations made
without any systematical view are those which are the most faithfully
described, and even this able naturalist no sooner formed a system on
spermatic animals, than he began to vary in essential points.
It is evident by the above dales, that Hartsoeker is not the first who
published, if he was the first who discovered spermatic animals. In
the Journal de Sçavans, in the year 1774, there is a letter from Mr.
Huguens, on the subject of a microscope, made by one small ball of
glass, with which he asserts he perceived animals in the water, wherein
pepper had been infused for two or three days, as Leeuwenhoek before
had observed with the like microscopes, but whose balls were not so
minute. "There are also other seeds, he continues, which engender such
animals, as coriander seeds, &c. and I have seen the same thing in the
pith of the birch tree, after having kept it for four or five days; and
some have observed them in the water where nutmegs and cinnamon have
been soaked. These animals may be said to engender from some corruption
or fermentation: but there are others which must have a different
origin; as those in the seed of animals, which seem in such great
numbers, as to be almost composed of them; they are all transparent,
have a quick motion, and their figures are like the tadpole."
Huguens does not mention the author of this discovery; but in the
Journal of the 29th of August in the same year, there is an extract
of a letter of M. Hartsoeker, in which he gives the method of forming
these glass balls by means of the flame of a lamp; and the author of
the Journal says, "By this method he has discovered that little animals
are engendered in urine which has been kept for some days, and have
the figure of little eels: he found some in the seed of a cock, which
appeared of the same form, but quite different from those found in the
seed of other animals, which resemble tadpoles, or young frogs, before
their legs are formed." The author seems to attribute the invention to
Hartsoeker; but if we reflect on the uncertain manner in which it is
there represented, and on the particular manner in which Leeuwenhoek
speaks in his letter, written and published above a year before, we
must allow him to be the first who made this observation; but between
them a contest took place as to the discovery which has never been
decided. Be this as it will, Leeuwenhoek was undoubtedly the first
inventor of the microscope, whose focuses are balls of glass formed by
the flame of a lamp. But to return to his observations.
I shall first remark, that what he says of the number and motion of
these pretended animals is true; but the figure of the body is not
always the same as he describes it: sometimes the part which precedes
the tail is round and at others long; often flat, and frequently
broader than it is long, &c. and with respect to the tail, it is often
much larger and shorter than he asserts. The motion of vibrations
which he gives to the tail, and by means of which he pretends that the
animalcules advance progressively in this fluid, has never appeared
to me as he has described it. I have seen these moving substances
make eight or ten oscillations from the right to the left, or vice
versa, without advancing the breadth of a hair; and I have even seen
many more which could not advance at all; because this tail, instead
of being of any assistance to them was, on the contrary, a thread
attached either in the filaments or mucilaginous parts of the liquor,
and rather retained the moving substance like as a thread fastened to
the point retains the ball of a pendulum; and when this tail had any
motion, it only resembled a thread which forms a curve at the end of
an oscillation. I have seen these threads, or tails, fastened to the
filaments which Leeuwenhoek stiles vessels; I have seen them separate
after many reiterated efforts of the moving bodies; I have seen them
at first lengthen, then diminish, and at last totally disappear. I
therefore think these tails should be considered as accidental parts,
and not as essential to the bodies of these pretended animals. But
what is most remarkable, Leeuwenhoek precisely says, in his letter
to Lord Brouncker, that, besides these animals that had tails, there
were also smaller animals in this liquor, which had no other form than
that of a globule. "His animalculis (caudatis scilicet) minora adhuc
animalcula, quibus non nisi globuli figuram attribuere possum, permista
erant." This is the truth; but after Leeuwenhoek had advanced that
these animals were the only efficient principle of generation, and that
they were transformed into human figures, he has only regarded those
as animals which had tails; and as it was consistent for animals that
were transformed into human figures, to have a constant form, he never
afterwards mentions those smaller animalcules without tails; and I
was greatly surprised, on comparing the copy of this letter with that
he published twenty years after, in his 3d volume, where, instead of
the above words, the following are found: "Animalculis hisce permistæ
jacebant aliæ minutiores particulæ, quibus non aliam quam globulorum
seu sphæricam figuram assignare queo;" which is quite different. A
particle of matter to which he attributes no motion, is very different
from an animalcule: and it is astonishing that Leeuwenhoek, in
copying his own works, has altered this essential article. What he
adds immediately after likewise merits attention: he says, that by
the desire of Mr. Oldenburg he had examined this liquor three or four
years before, when he took these animalcules for globules; that is,
there are times when these pretended animalcules are no more than
globules, without any remarkable motion, and others when they move with
great activity; sometimes they have tails, and at others they have
none. Speaking in general of spermatic animals he says, "Ex hisce
meis observationibus cogitare coepi, quamvis antehac de animalculis
in seminibus masculinis agens, scripserim, me in illis caudas non
detexisse, fieri tamen posse ut illa animalcula æque caudis fuerint
instructa ac nunc comperi de animalculis in gallorum gallinaceorum
semine masculino;" another proof that he has often seen spermatic
animals of all kinds without tails.
In the second place we must remark, that the filaments which are
seen in the seminal liquor before it is liquefied were discovered by
Leeuwenhoek, and that in his first observations, before he had made
any hypothesis on spermatic animals, he considered these filaments as
veins, nerves, and arteries; and firmly believed all the parts and
vessels of the human body might clearly be seen in the seminal liquor.
This opinion he persisted in, in defiance of the representations
which Oldenburg made to him on this subject from the Royal Society:
but as soon as he thought of transforming these pretended spermatic
animals into men, he no longer mentioned these vessels; and instead
of looking on them as nerves, arteries, and veins, of the human body
already formed in the seed; he did not even attribute to them the
functions they really possess, the producing of these moving bodies:
and he says, vol. I. p. 7, "Quid fiet de omnibus illis particulis seu
corpusculis præter illa animalcula semini virili hominum inhærentibus?
Olim & priusquam hæc scriberem, in ea sententia fui, prædictas strias
vel vasa ex testiculis principium secum ducere, &c." And in another
part he says, that if he had formerly written any thing on the subject
of these vessels found in the seed, we must pay no attention to it.
[Illustration: _PLATE. IV._]
We shall observe in the third place, that if we compare the figures
_a, b, c, d_, (PLATE III.) copied from the Philosophical Transactions,
with those which Leeuwenhoek had engraved many years after, (PLATE IV.)
we shall find considerable difference, especially in the figures of
the dead animals, of a rabbit and in those of a dog, (which plate we
have also copied for the satisfaction of our readers) from all which
we may conclude, that Leeuwenhoek has not always observed objects
entirely alive: that the moving bodies, which he looked upon as
animals, appeared to him under different forms; and that he has varied
in his assertions, with a view of making the species of men and animals
perfectly consistent; he has not only varied in the basis of these
experiments, but even in the manner of making them, for he expressly
says, that he always diluted the liquor with water, in order to
separate, and to give more motion to these animalcules: nevertheless,
in his letter to Lord Brouncker, he says, that having mingled an equal
quantity of rain water with the seminal liquor of a dog, in which he
had before perceived an infinity of living animalcules, yet the mixing
of this water killed them. The first experiment of Leeuwenhoek's
therefore was made, like mine, without any mixture; and it even seems,
that he was not of opinion to mix any water with the liquor till a
long time after; because he thought he had discovered, by his first
essay, that water caused the death of the animalculæ; which however is
not the fact. I think that the mixture of the water only dissolves the
filaments very suddenly; for I have seen but very few filaments in all
the experiments I have made after mixing the water with the seminal
liquor.
As soon as Leeuwenhoek was persuaded that spermatic animals were
transformed into men, and other animals, he imagined he saw two sorts
in the seminal liquor of every animal, the one male, and the other
female; and this difference, according to him, served not only for the
generation of themselves, but for the production of males and females,
which was very difficult to conceive by a simple transformation. He
speaks of the male and female animalcule, in his letter printed in the
Philosophical Transactions, No. 145, and in many parts of his works,[U]
but he does not describe the difference of these male and female
animalcules, and which in fact never existed but in his own imagination.
[U] See vol I. page 163, and vol. III. page 101, of his works.
The famous Boerhaave having asked Leeuwenhoek, if he had not observed
in spermatic animals different degrees of growth and size? Leeuwenhoek
answered, that having dissected a rabbit, he observed in the semen an
infinite number of living animals. "Incredibilem, says he, viventium
animalculorum, numerum conspexerunt, cum hæc animalcula scypho
imposita vitreo & illic emortua, in rariores ordines disparassent, &
per continuos aliquot dies sæpius visu examinassem, quædam ad justam
magnitudinem nondum excrevisse adverti. Ad hæc quasdam observavi
particulas perexiles & oblongas, alias aliis majores, &, quantum oculis
apparebat, cauda destitutas; quas quidem particulas non nisi animalcula
esse credidi, quæ ad justam magnitudinem non excrevissent."[V]
Here then are animalcules of different sizes, some with tails and
others without, which much better agrees with my experiments, than
with Leeuwenhoek's own system. We differ only in one particular; he
says, that those without tails were young animalculæ, which were not
arrived at their full growth; while I, on the contrary, have seen
these pretended animals quit the filaments with tails or threads, and
afterwards lose them by degrees.
[V] See vol. IV. pages 280 and 281.
In the same letter to Boerhaave, he says, in the semen of a ram, he
perceived animalcules following each other in swarms like a flock of
sheep. "A tribus circiter annis testes arietis, adhuc calentes, ad ædes
meas deferri curaveram, cum igitur materiam ex epididymibus eductam,
ope microscopii contemplarer, non sine ingenti voluptate advertebam
animalcula omnia, quotquot innatabant semini masculino, eundem
natando cursum tenere, ita nimirum ut quo itinere priora prinatarent
eodem posteriora subsequerentur, adeo ut hisce animalculis quasis
sit ingenitum, quod oves factitare vidimus, scilicet ut precedentium
vestigiis grex universus incedat." This observation, which Leeuwenhoek
made in 1713, and which he looks upon as singular and novel, proves
to me, that he had never examined the seminal liquors of animals with
attention, at least sufficient to give very exact descriptions of them.
Leeuwenhoek was sixty-one years old in 1713, had made microscopical
observations for more than forty-five years, had published the
discovery of spermatic animals for about thirty-six years, and then,
for the first time, saw in the seminal liquor of a ram, what is seen in
all seminal liquors, and what I have described in Experiment IX. in the
seed of a man; Experiment XII. in the seed of a dog; and in Experiment
XXIX. in that of a bitch. It is not necessary to suppose the spermatic
animals of the ram are endowed with instinct, to explain the floating
of these animals, in flocks like sheep, since those of a man, dog, or
bitch, does the same; and which motion depends solely on particular
circumstances, whose principle is, that all the fluid matter of the
seed is on one side, while the thick matter is on the other; for then
all the bodies in motion will be disengaged from the mucilage, and
follow the same road into the most fluid part of the liquor.
In another letter, written the same year, to Boerhaave, he relates some
further observations he made on rams, and says, that he has seen, in
the _vasa deferentia_, flocks of animals which float all on one side,
and others which go in a contrary direction; and he adds, "Neque illud
in unica epididymum parte, sed & in aliis quas præcideram partibus,
observavi. Ad hæc, in quadam parastatarum resecta portione complura
vidi animalcula, quæ necdum in justam magnitudinem adoleverant, nam
et corpuscula illis exiliora & caudæ triplo breviores erant quam
adultis. Ad hæc, caudas non habebant desinentes in mucronem, quales
tamen adultis esse passim comperio. Præterea in quandam parastatarum
portionem incidi, animalculis quantum discernere potui, destitutam,
tantum illi quædam perexiguæ inerant particulæ, partim longiores,
partim breviores, sed altera sui extremitate crassiunculæ; istas
particulas in animalcula transituras esse non dubitabam." It is easy
to see, by this passage, that Leeuwenhoek had seen, in this seminal
liquor, what I found in all; that is to say, moving bodies of different
sizes, figures, and motions; and which agrees much better with the idea
of organic particles in motion than of that with real animals.
It appears, therefore, that Leeuwenhoek's observations are not contrary
to mine, although he has drawn very different conclusions from them. I
am persuaded that if any person would take the trouble of making the
like experiments they would not have any difficulty in discovering from
whence these differences proceed, and would find that I have advanced
nothing which is not conformable to truth; and to enable the reader to
decide thereon, I shall subjoin a few remarks.
The filaments I have spoken of are not always to be perceived in the
seminal liquor of a man. To discover them it must be examined the
moment it is taken from the body, and even then it will sometimes
happen that there is not one to be seen. Sometimes the seminal liquor
presents, especially when it is very thick, only large globules, which
may be even distinguished with a common lens. By inspecting them with
the microscope they appear like young oranges; they are very opaque,
and a single one often fills up the whole table of the microscope.
The first time I saw these globules I thought they were some foreign
matters fallen into the liquor, but having examined different drops
I discovered that the whole was composed of these thick globules. I
selected one of the roundest, and whose size was such that, its centre
being in the middle of the table of the microscope, I could at the
same time observe the whole circumference; at first it was absolutely
opaque; a short time afterwards I perceived a bright luminous ring
to form on its surface, which remained about half an hour, and then
approached by degrees towards the centre, which became clear, and of
different colours, while the remainder of the globule continued opaque.
This light, which brightened in the centre of the globule, resembled
those seen in the great air bubbles. The globule then began to get
a little flat, and acquire a small degree of transparency. Having
examined it more than three hours I perceived no more alteration,
nor any appearance of motion, either internally or externally. I
then imagined, that by mixing this liquor with water, these globules
might be changed; in fact they did change, but they presented only a
transparent and homogeneous liquor, wherein was nothing remarkable. I
suffered the seminal liquor to liquefy of itself, and examined it at
the end of six, twelve, and twenty-four hours, but saw nothing more
than a fluid; without the smallest resemblance of life or motion. I
only relate this observation to shew that there are times when the
common phenomena are not to be seen in the seminal liquor.
At times all the moving bodies appear to have tails, especially in
the semen of a man and a dog; the motion is then the least brisk, and
performed with difficulty. If this liquor is suffered to dry, the tails
or threads are deprived of motion the first; the anterior extremity
continues to vibrate for some time, and then all motion entirely
ceases. These substances may be preserved in this state of dryness for
a long time: if a small drop of water is mixed therewith, their figure
changes, they are reduced into many globules, which sometimes appear to
be in motion, as well by their approximation to each other, as by the
trepidation and twirling round their centres.
These moving bodies in the seminal liquor of a man, dog, or bitch, so
nearly resemble each other, as to admit of mistaking one for the other,
especially if they are examined the moment the liquor is drawn from
the animal. Those of the rabbit appear smaller and brisker; but these
differences proceed more from the different states in which the liquor
is at the time of observation, than from the nature of the liquor
itself, which ought to be different in different kinds of animals;
for example, in that of a man I have seen streaks of thick filaments,
(_fig. 3._) and have perceived the moving bodies separate themselves
from these filaments from whence they appeared to proceed; but I have
never seen any thing like it in the semen of a dog; where, instead
of filaments, or separated streaks, it is commonly a mucilage whose
texture is more compact, and in which we with difficulty discern any
filamentary parts; yet this mucilage gives birth to moving bodies like
those in the semen of men.
The motions of these bodies remain a longer time in the liquor of a
dog, than in that of a man; from which it is more easy to be certain of
the alteration of form above mentioned. The moment the liquor issues
from the body of the animal we perceive the animalcules to have tails;
in twelve, twenty-four, or thirty-six hours after, we shall find they
have lost those tails, and are then no more than ovals in motion, often
much brisker than at first.
The moving bodies are always a little below the surface of the liquor.
On the surface some large transparent air bubbles, which have no
motion, generally appear, though sometimes these bubbles stir and
seem to have a progressive motion, but which is nothing more than the
agitation of the air. Below the moving substances we often see others
much smaller, and which only appear like globules, having no tails,
but the greatest number of which are oftentimes in motion. I have
also generally remarked, that in the infinite number of globules, in
all those liquors, those which are very small, are commonly black, or
darker than the rest; and that those which are extremely minute and
transparent, have but little or no motion; they appear also to weigh
specifically heavier, for they are always the deepest in the liquor.