Some account of L.’s experiments “on the compression of the air”
had already appeared in Phil. Trans. (1673), Vol. IX, p. 21. (Letter 2,
15 August 1673. MS. Roy.Soc.)
* “four days”’ Saville Kent (Vol. I, p. 3). This is merely due to careless
copying, and is not in the originals.
. . . . be
* in een nieuwe ton, die van binnen blaww geverft was MS. in a new
earthen pot, glased blew within’ Phil. Trans. Oldenburg here mis-
translated L.’s words, which were quite plain and were rendered concordantly
by Chr. Huygens “dans un tonneau peint en huile par dedans’”’. The vessel
was obviously not of Delft porcelain.
° ¢.e., in bulk—not in diameter. This expression means, with L., that
he judged the animalcules to have roughly one twenty-fifth of the diameter
of the bigger creatures.
® Jan Swammerdam (1637—1680). For his life see especially his
Biblia Naturae (1737) and Sinia (1878).
118 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”
Water-flea, or Water-louse,’ which you can see alive and
moving in water with the bare eye.
Of the first sort that I discovered in the said water, I
saw, after divers observations, that the bodies consisted
of 5, 6, 7, or 8 very clear globules, but without being able
to discern any membrane or skin that held these globules
together, or in which they were inclosed. When these
animalcules bestirred ’emselves, they sometimes stuck
out two little horns,’ which were continually moved, after
the fashion of a horse’s ears. The part between these
little horns was flat, their body else being roundish, save
only that it ran somewhat to a point at the hind end; at
which pointed end it had a tail, near four times as long
as the whole body, and looking as thick, when viewed
through my microscope, as a spider’s web.* At the end
of this tail there was a pellet, of the bigness of one of the
globules of the body; and this tail I could not perceive
to be used by them for their movements in very clear
water. These little animals were the most wretched
creatures that I have ever seen; for when, with the
pellet, they did but hit on any particles or little filaments °
(of which there are many in water, especially if it hath
* Swammerdam’s “ watervlooy’”’ was Daphnia—as all students of the
Biblia Naturae are well aware (cf. B.N. Vol. I, p. 86, Pl. XX XI). But as this
work was not published until 1737—long after his death—it is clear that
L. here alludes to his earlier Dutch publication (Swammerdam, 1669), in
which the water-flea is shown on Pl. I. Swammerdam himself called it
“the branched water-flea”’, and attributed the name ‘‘ water-louse’’ to
Goedaert.
> Vorticella sp. The following admirable description makes the
identification certain.
* The optical section of the wreath of cilia round the peristome—so
interpreted by most of the early observers.
* i.e., as thick as a spider’s web looks to the naked eye.
a9
> maer quamen aen eenige deeltgens of veseltgens MS. ° if they chanced
to light upon the least filament or string, or other such particle’? Phil.
Trans. These words of Oldenburg are amusingly mistranslated by Nagler
(1918, p. 7) ““ Wenn man diese kleinen Kreaturen Zufallig belichtete.” (He
apparently supposes that “ to light upon’”’ means “‘ to illuminate ” ! )
LETTER 18. RAIN-WATER 119
but stood some days), they stuck intangled in them; and
then pulled their body out into an oval, and did struggle,
by strongly stretching themselves, to get their tail loose ;
whereby their whole body then sprang back towards the
pellet of the tail, and their tails then coiled up serpent-
wise, after the fashion of a copper or iron wire that,
having been wound close about a round stick, and then
taken off, kept all its windings.’ This motion, of stretch-
ing out and pulling together the tail, continued; and I
have seen several hundred animalcules, caught fast by
one another in a few filaments, lying within the compass
of a coarse grain of sand.”
I also discovered a second sort* of animalcules, whose
figure was an oval; and I imagined that their head was
placed at the pointed end. These were a little bit bigger
than the animalcules first mentioned. ‘Their belly is flat,
provided with divers incredibly thin little feet, or little
legs,* which were moved very nimbly, and which I was
able to discover only after sundry great efforts, and where-
with they brought off incredibly quick motions. The
upper part of their body was round, and furnished inside
with 8, 10, or 12 globules: otherwise these animalcules
* Apparently it never occurred to L., at this time, that the contraction
and extension of the stalk (“tail’’) of Vorticella could have any other
significance than that here attributed to them. The idea of a stalked and
normally sessile animal probably never entered his head; and consequently
he jumped to the incorrect conclusion that the animals were endeavouring
to “ get their tails loose ’’—which, of course, was a mistake, though a very
natural one. lL. published pictures of Vorticellids later, in Phil. Trans.,
Vol. XXIII (Letter dated 25 Dec. 1702): and still later he arrived at a
more correct interpretation of the function of the “tail,” and of the
organization of these remarkable animals (Send-brief VII, dated 28 June
1713). See Chapter 4, below.
* inde spatie van een grof sant MS. “ within the space of a grain of gross
sand” Phil. Trans. This is a very common expression with L., and
Oldenburg fully understood its meaning ; but Nagler (1918, p. 9) mistranslates
his words “in der Héhlung eines grossen Sandkorns’’—as though L. had seen
the animalcules lying in a cavity in an actual grain of sand!
* Not identifiable with certainty, but undoubtedly a ciliate.
y Ve ey:
2.e. cilia.
120
LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”
were very clear. These little animals would change their
body into a perfect round, but mostly when they came to
lie high and dry. Their body was also very yielding: for
if they so much as brushed against a tiny filament, their
body bent in, which bend also presently sprang out again ;
just as if you stuck your finger into a bladder full of
water, and then, on removing the finger, the inpitting
went away. Yet the greatest marvel was when I brought
any of the animalcules on a dry place, for I then saw
them change themselves at last into a round, and then the
upper part of the body rose up pyramid-like, with a point
jutting out in the middle; and after having thus lain
moving with their feet for a little while, they burst
asunder, and the globules and a watery humour flowed
away on all sides, without my being able to discern even
the least sign of any skin wherein these globules and the
liquid had, to all appearance, been inclosed ; and at such
times I could discern more globules than when they were
alive. This bursting asunder I figure to myself to happen
thus: imagine, for example, that you have a sheep’s
bladder filled with shot, peas, and water; then, if you
were to dash it apieces on the ground, the shot, peas, and
water would scatter themselves all over the place.’
Furthermore, I discovered a third sort’ of little
animals, that were about twice as long as broad, and to
my eye quite eight times smaller* than the animalcules
first mentioned: and I imagined, although they were so
small, that I could yet make out their little legs, or little
fins. Their motion was very quick, both roundabout and
in a straight line.
ee ee
* The foregoing graphic account of the bursting of the “ little animals” is
of great interest, as it shows clearly that L. was really observing protozoa.
An animal whose body consisted entirely of soft ‘‘ protoplasm ”—without any
skeletal parts or obvious skin—was, of course, a considerable novelty at this
date.
2
Not identifiable. Probably a small ciliate.
* «.e., having a diameter equal to about half that of the Vorticella.
LETTER 18. RAIN-WATER 121
The fourth sort! of animalcules, which I also saw
a-moving, were so small, that for my part I can’t assign
any figure to em. These little animals were more than
a thousand times less than the eye of a full-grown
louse? (for I judge the diameter of the louse’s eye to be
more than ten times as long as that of the said creature),
and they surpassed in quickness the animalcules already
spoken of. I have divers times seen them standing still,
as ’twere, in one spot, and twirling themselves round
with a swiftness such as you see in a whip-top a-spinning
before your eye*; and then again they had a circular
motion, the circumference whereof was no bigger than
that of a small sand-grain; and anon they would go
straight ahead, or their course would be crooked."
Furthermore, I also discovered sundry other sorts of
little animals; but these were very big, some as large as
the little mites on the rind of cheese, others bigger and
very monstrous.’ But I intend not to specify them ; and
1 Probably—from the ensuing description—a species of Monas. Certainly
not bacteria of any kind.
2 This makes the diameter of the protozoon here described about 6-8 p,
and is agreeable with its interpretation as Monas vulgaris.
? If the description applies to Monas—as I strongly suspect—then the
“spinning” here described was an illusion. I fancy L. saw a Monas attached
by its caudal filament, and mistook the swirl of the water at its anterior
end (occasioned by the movements of the small accessory flagellum) for a
motion caused by the rotation of the body as a whole.
4 on dan weder soo regt wijt, als crom gebogen MS. These words are hard
to understand. The above seems to me to be L.’s meaning : but Oldenburg
translates ‘and then extending themselves streight forward, and by and by
lying in a bending posture ”’ (Phil. Trans.). It is hardly likely that L. could
have observed “a bending posture”’ in an organism so small that he could
discern “ no figure” in it: and as the “circular motion” just mentioned
evidently refers to the orbit described by the organism—not to the
animalcule itself—I imagine that ‘‘regt wijt’” and “‘ crom gebogen” likewise
refer to the path traversed. I should point out, however, that L. elsewhere
(Letter 38) applies precisely the same words to the shape of the spermatozoa
of a frog.
® Some of these were doubtless protozoa, but the “ monsters’ were
perhaps rotifers. Much later, when describing these animals, L. mentions
that he had previously discovered them in rain-water, in which he had
steeped pepper and ginger. See Letter 144, 9 Feb. 1702.
122 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS ”’
will only say, that they were for the most part made up
of such soft parts, that they burst asunder whenever the
water happened to run off them.
The 2nd Observation. [Rain-water.]
The 26th of May,’ it rained very hard. The rain
abating somewhat, I took a clean glass and got
rain-water, that came off a slate roof, fetched me in it,
after the glass had first been swilled out two or three
times with the rain-water. I then examined it, and
therein discovered some few very little animals’; and
seeing them, I bethought me whether they might not
have been bred in the leaden gutters, in any water that
might erstwhile have been standing in them.
The 3rd Observation. Rain-water.
On the same date, the rain continuing nearly the
whole day, I took a big porcelain dish, and put it in
my court-yard, in the open air, upon a wooden tub
about a foot and a half high: considering that thus no
earthy particles would be splashed into the said dish by
the falling of the rain at that spot. With the water
first caught, I swilled out the dish, and the glass in
which I meant to preserve the water, and then flung this
water away: then, collecting water anew in the same
dish, I kept it; but upon examining it, I could discover
therein no living creatures, but merely a lot of irregular
earthy particles.
The 30th of May, after I had, since the 26th, observed
this water every day, twice or thrice daily, I now first
discovered some (though very few) exceeding little
animalcules,* which were very clear.
* Anno 1676.
* Unidentifiable. The animalcules from L.’s gutters were described by
himself later. (Cf. p. 263 infra.) They include flagellates, ciliates, bacteria,
and rotifers.
* From the description which follows, these were probably the same
as the “ very little animalcules”’ already described—.e., a species of Monas.
LETTER 18. RAIN-WATER 123
On the 31st ditto, I discovered more little animals in
the water, as well as a few that were a bit bigger; and I
imagine that ten hundred thousand of these very little
animalcules are not so big as an ordinary sand-grain.’
Comparing these animalcules with the little mites in cheese
(which you can see a-moving with the bare eye), I would
put the proportion thus: As the size of a’small animalcule
in the water is to that of a mite, so is the size of a honey-
bee to that of a horse; for the circumference of one of
these same little animalcules is not so great as the thick-
ness of a hair on a mite.
The 4th Observation. Rain-water.
On June 9th,’ collected rain-water betimes in a dish, as
aforesaid, and put it at about 8 o’clock in the morning in
a clean wine-glass, and exposed it to the air at about the
height of the third storey of my house, wondering whether
the little animals would appear sooner in water thus
standing in the air.
The 10th ditto, observing this water, I fancied that I
discovered living creatures; but because they were so
few, and not so plainly discernible, I could not accept
this for the truth.
On the 11th ditto, seeing this water, with the naked
eye, stirred in the glass by a stiff gale of wind (which had
now blown from the same quarter for 36 hours; the
weather being so cold withal, that it did not irk me to
wear my winter clothes), I had no thought of finding any
living creatures in it; but upon examining it, I saw with
wonder quite 1000 living creatures in one drop of water.
‘This means that he estimated their diameter at something less than
zdo of the diameter of an “ordinary” (or large) sand-grain. Taking this
as 35 of an inch, their diameter would thus be of the order of so00 in., or
roughly 8°5. This is a very close guess at the size of Monas vulgaris. On
sand-grains cf. p. 334 fra.
? Anno 1676.
124 LEEUWENHOEK AND HIS “LITTLE ANIMALS”’
These animalcules were of the smallest sort’ that I had
as yet seen.
The 12th of June, in the morning (the wind being west,
with both sunshine and an overcast sky), observing again,
I saw the foresaid animalcules in such great numbers in
the water which I took from the surface, that now they
did not amount to merely one or two thousand in one
drop.
The 13th ditto, in the morning, examining the water
again, I discovered, besides the foresaid animalcules, a
sort of little animals that were fully eight times as big’
as the first; and whereas the small animalcules swam
gently among one another, and moved after the fashion
of gnats in the air, these large animalcules had a much
swifter motion; and as they turned and tumbled all
around and about, they would make a quick dart.°®
These animalcules were almost round. *
On the 14th of June I did perceive the very little
animalcules in no less number.
On the 16th ditto, the animalcules seen as before; and
the water (which had been, in all, about 4 of a pint)
being now more than half dried up, I flung it away.
5th Observation. Rain-water.
The 9th of June,’ I put some of the last-collected
water, likewise in a clean wine-glass, in my closet; and
*4.e., probably Monas sp. again.
? On L.’s system this means “ twice as long”.
= nmamen deselve een snelle scheut MS. “and then making a sudden
downfall”? Phil. Trans. L.’s meaning seems clearly to be that given above
(i.e., they sometimes made sudden shoots or darts forward). Oldenburg
renders his words as though scheut = Fr. chute.
4 It seems to me almost certain that the animalcule here described was
the common ciliate Cyclidiwm. This is the only likely organism—of this
order of magnitude—which makes sudden springs (hence its name of “ flea-
animalcule”’). The only objection to this interpretation is the statement
that it was ‘‘almost round’’: but it must be remembered that L. made
his observations under a very inadequate magnification.
> Anno 1676.
iat int ‘ag FY eo
ay Oi
by set) Gains
re
PLATE XX
Rijksmuseum
Amsterdam
A HOUSE IN DELFT
From the picture by Jan Vermeer (1632-1675). This three-storey house is
probably very like the one in which Leeuwenhoek lived. The picture shows
the casement windows, with their leaded panes and wooden shutters, and
an alleyway leading to the yard at the back (where the well was situated) :
only the canal in front of the house is not shown below the cobbled
pavement in the foreground.
facing p. 125
LETTER 18. RAIN-WATER 125
on examining it, I descried no animalcules. (Note. My
closet standeth towards the north-east,’ and is parti-
tioned off from my antechamber with pine-wood, very
close joined, having no other opening than a slit an inch
and a half high and 8 inches long, through which the
wooden spring of my lathe passeth. ‘Tis furnished
towards the street with four windows, whereof the two
lowermost can be opened from within, and which by
night are closed outside with two wooden shutters; so
that little or no air comes in from without, unless it
chance that in making my observations I use a candle,
when I draw up one casement a little, lest the candle
inconvenience me; and I also then pull a curtain almost:
right across the panes.)
The 10th of June, observing this foresaid rain-water,
which had now stood about 24 hours in my closet, I
perceived some few very little living creatures,’ to which,
because of their littleness, no figure can be ascribed; and
among others, I discovered a little animal that was a bit
bigger, and that I could perceive to be oval.* (Note.
When I say that I have observed the water, I mean I
have examined no more than 3, 4, or 5 drops thereof,
which I also then throw away; and in narrowly
scrutinizing 3 or 4 drops I may do such a deal of work,
that I put myself into a sweat.)
' From the situation of the house, this indicates that the “ closet”? was
at the front, looking on to the canal in the Hippolytusbuurt.—Plate XX is
inserted here to show the sort of house which L. probably lived in, and to
illustrate what he means by fowr windows with two wooden shutters over
the lowermost. (This picture may conceivably have been painted from L.’s
own house—or Vermeer’s!) Although the original painting (formerly in
the Six Collection, now in the Rijksmuseum) is now known as Het Straatje
(= The Little Street), it appears to have been more correctly described as
“A View of a House in Delft” in the catalogue of the sale of Vermeer’s
pictures at Amsterdam in 1696.
* Probably Monas (or Cercomonas): see below.
* From the observations recorded later, it appears probable that the
organism was a ciliate; but its very small size is against this interpretation.
It may have been a Cyclidiwm.
126
LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
The 11th ditto, observing this water again, I saw the
foresaid small animalcules, though very few in number.
The 12th ditto, I saw the very small animalcules, as
yesterday ; and besides these, a little animal’ that had
nearly the figure of a mussel-shell, lying with its hollow
side downwards. “T'was of a length anigh that of a
louse’s eye.”
The 13th ditto, in the morning, I found the said very
small animalcules in greater number, and I saw also one
bigger animalcule, like that just spoken of.” The same
day, in the evening, I perceived the said very small
animalcules again in no less number; and I could now
see that they had a clear or transparent projection at the
hind end of their body.* Moreover I discovered animal-
cules which were somewhat longer than an oval.’ These
were about 6 times as long as the foresaid very small
animalcules ; and their head, which was somewhat long
drawn out, they oft-times pulled in, and then looked to
be almost round. ‘There were also animalcules’ which
appeared perfectly round, their diameter being twice as
long as that of the smallest animalcules of all. These
two large sorts were very yielding, so that their body did
bend before the least little filament which they chanced
to brush against in the water.
The 14th ditto, I perceived the oval animalcules in
greater number.’
' Traditionally—and doubtless with justice—identifiable as Stylonychia
mytilus (O.F.M.) Ehrbg., a common hypotrichous ciliate.
* That is, about 70m. See p. 336.
*ie., Stylonychia.
* Probably Monas again—or perhaps a Cercomonas.
® From the description which follows it seems probable that these were
Dileptus sp., but it is impossible to identify them with certainty.
© Perhaps Cyclidiwm again — similarly described on June 13 (4th
observation).
7This apparently refers to the oval animalcules seen on the 10th
(2 Cyclidiwm).
LETTER 18. RAIN-WATER 127
The 16th ditto, I perceived the oval animalcules in yet
greater numbers; and they were flat beneath, and round
above: and besides these, there were very small animal-
cules that were three times as long as broad,’ together
with divers other sorts which it would take all too long
to specify. In the evening of the same day, I discovered
little paws on the foresaid oval animalcules,’ which were
many in number, in proportion to the animalcule; and
also a much bigger animalcule* of the same figure, that
was likewise furnished with little legs. And at this point,
I stopped my observations upon this water.
6th Observation anent Rain-water.
On the 17th ditto, it rained very hard in the forenoon,
and I collected water, as before related, in a new Delft
porcelain dish, which had never been used before; but I
found therein no living creatures, only many earthy
particles, and, among others, bits which I imagined came
from the smoke of coals’; and some very thin threads, at
least ten times thinner than the thread of a silk-worm.
They seemed to be made up of globules; and when they
lay rather thick one upon another, they had a green
colour.
The 26th ditto, having been eight days out of town
on holiday, and my closet having stood tight shut up;
being come home, and observing the water afresh, I
discovered divers animalcules, which were very small.°
* Unidentifiable, as no further details are given. Possibly Bodo
caudatus.
” 2? Cyclidium. The “paws” were obviously cilia.
* A ciliate; but not determinable, as this is all that is ever said about it.
* June, 1676.
° wande rook van smits coolen MS. “from the smoak of Smiths-coals”
Phil. Trans. “ Smits coolen”’? means ordinary (or stone) coal, as dis-
tinguished from “ howts coolen’’, or charcoal. The “globules” present in
smoke are described by L. elsewhere.
° Unidentifiable. It is not clear from his words whether L. here refers
to the ‘‘ very small animalcules’”’ (Monas?) previously mentioned or not.
128 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS ”’
Thereupon I put my observations upon rain-water on one
side for the time being.
[ Observations on River-water. |
This town of Delft is very well off for water, and in
summer we get fresh water into the town with all the
floods seaward from the river Maas; wherefore the water
within the town is very good, and river fish are caught
every day by children with fishing-rods in the water-
ways inside the town. This water being divers times
examined by me, I discovered in it some exceeding small
animalcules (so small, indeed, that I could scarce discern
their figure) of sundry sorts and colours, and therewithal
some that were much bigger; though were I to specify
the motion and the make of every one of ’em, ’twould
take all too long a-writing. But all these animalcules are
very scanty in this water, compared with those that I saw
in the rain-water; for if I discovered 25 animalcules in
one drop of it, that was quite a lot.’
[Observations on Well-water.]
I have in my yard,’ standing in the open air, a well,
which is about 15-foot deep before you come to the
water. It standeth at the south, but so encompassed
with high walls, that even when the sun is in the sign of
Cancer, the coping of the well is not shone upon. This
water cometh out of the ground, which is well-sand, with
such force, that whenever I have tried to empty the well
there was always about a foot of water still leftin. On
a summer’s day this water is so cold that ’tis not feasible
to keep your hand in it for long. Having no thought
that there would be living creatures in it (for ’tis very
1 No identification of these “animalcules”’ can be attempted, though
they must have been protozoa or bacteria. As some of them were coloured,
it may be inferred that they included Phytoflagellates.
> op mijn plaets MS. “In the open Court of my house’? Oldenburg
dans ma cour Huygens.
PLATE
XX
I
THE SHORE AT SCHEVENINGEN
as it appeared in Leeuwenhoek’s time.
National Gallery
facing p. 129
by Jacob van Ruisdael (1628 ?- 1682).
ing
t
-pain
il
After the o
LETTER 18. RIVER,- WELL,- SEA-WATER 129
palatable and clear), I examined it in September of last
year, and discovered therein a great number of very
small animalcules, which were very clear, and a bit bigger
than the very smallest animalcules that I’ve ever seen.
And I imagine (having aforetime weighed a grain of
water), that there were commonly more than 500 living
creatures in one grain of this water. ‘These animalcules
were very sedate, moving without any jerks.”
In the winter’ I perceived no little animals, nor did I
see any of them this year before the month of July, and
then not in such great plenty; but in the month of
August, their number was much increased.
[ Observations on Sea-water.|
The 27th of July, 1676, I betook myself to the seaside,
hard by the village of Schevelinge.* Finding myself upon
the shore (the wind coming off the sea, with very warm
sunshine), and observing the sea-water as well as I could,
I discovered in it divers living animalcules. I gave to a
certain person, who went into the sea to bathe himself, a
—_—_—__
‘G.e., anno 1675.
* dese diertgens waren seer sedig, sonder eenige horten in haer beweginge
MS. - + + Were very quiet and without motion” Phil. Trans.—
Oldenburg’s translation is clearly wrong, and entirely changes the meaning
of this passage. The organisms were probably very small flagellates
(? Cercomonas sp.): and I imagine that L. is here contrasting their even
(creeping) movements with the jumping motions of the Cyclidiwm which he
had previously seen in rain-water.—According to Sewel (1708), hort means
“a Hunch, push, jog, tug”: and to do a thing “ met horten en stooten”’
signifies to do it “ by fits and starts”, as we now say.
* Presumably 1675-1676.
* Now called Scheveningen—the well-known sea-side resort near The
Hague: but the name is so spelled by L. here and elsewhere (cf. Send-brief
XLII, 10 Sept. 1717), as it is in some old Dutch maps which I have
examined. Pepys, in his Diary, also calls the place ‘ ‘ Scheveling, ” while
Temple (1693), our Ambassador to Holland in 1668, writes ‘Skeveling ”’ ;
and Professor Beijerinck informs me further that the spelling © Schevelingen ”’
was sometimes used formerly. The appearance of the ‘‘ Shore at Schevelinge ”’
in L.’s day is shown in the well-known picture by Jacob van Ruisdael (1628-
1682) in the National Gallery (No. 1390). See Plate XXI.
9
130 LEEUWENHOEK AND HIS “LITTLE ANIMALS’”’
new glass phial (which I had bought on purpose) and
besought him that, when he was in the sea, he would
rinse it out twice or thrice and then fill it up with water.
This having been carried out according to my orders, I
tied the phial up tight with a clean bit of bladder: and
on reaching home and examining the water, I perceived
therein a little animal’ that was blackish, having a shape
as if twere made of two globules. This little animal had
a peculiar motion, after the manner of a very little flea,
when seen, by the naked eye, jumping on a white paper ;
yet ’twas only displaced, at every jump, within the com-
pass of a coarse sand-grain, or thereabouts. It might
right well be called a water-flea; but ’twas not so big,
by a long way, as the eye of that little animal which
Swammerdam calls the Water-flea.”
I did also discover animalcules which were clear, of the
same bigness as that first mentioned; but they had an
oval figure, and their motion was snake-wise.
Furthermore, I perceived yet a third sort, which were
very slow in their motion. Their body was mouse-colour ;
and they were also a bit on the oval side,’ save that a
sharp little point stuck out (sting-fashion) * in front of the
head, and another at the hind end. This sort was a bit
bigger.
And there was besides a fourth sort, rather longer than
an oval. Yet all these animalcules were few in number,
so that in a drop of water I could make out but 3 or 4,
nay, sometimes but one.
* Iam unable even to hazard a guess at the identity of this organism ;
but, judging from its estimated size, it may well have been a protozoon.
> i.e., Daphnia. Cf. p. 118, note 1.
° mede hellende na de ovale kant MS. “clear towards the oval-point ”’
Phil. Trans.—an evident mistranslation. LL. means that their shape tended
to be oval—not that they were clear at one end. I translate his colloquial
old Dutch into its equivalent in modern conversational English.
* angels gewijs MS. “‘angle-wise” Phil. Trans. Angel means a sting
(e.g., that of a bee), not an angle (=hoek). lL. was probably thinking of the
mouth-parts of a mosquito—which he also called (as the man-in-the-street
still does) its “‘sting”’. ;
ce
LETTER 18. SEA- AND PEPPER-WATER 131
The 31st ditto, having examined this water every day
since the 27th, and perceived no little animals in it;
upon this date I did now see a good hundred of ’em where
at first I had seen but one: but they were now of another
figure, and not only smaller, but also very clear. They
were like an oblong oval, only with this difference, that
they tapered somewhat more sharply to a point at what
I imagined to be the head end. And although these were
at least a thousand times smaller than a very small sand-
grain, I saw, notwithstanding, that whenever they lay
high and dry out of the water they burst asunder, and
flowed apart or scattered into three or four very small
globules and some watery matter, without my being able
to discern any other parts.’ (In the above, I took the
water out of the phial from the surface: and at this time,
too, I was no longer able to see the animalcules of the
sort first spoken of.)
The 2nd of August I could discern nought but an
abundance of the foresaid animalcules.
The 4th ditto, saw ’em as heretofore, without any
difference.
The 6th of August, looking again, perceived nowhere
near as many little animals.
The 8th ditto, I again discovered a very few of the
. foresaid animalcules; and I now saw a few so exceeding
small that, even through my microscope, they well-nigh
escaped the sight. And here I stopped my observations.”
[Observations on Pepper-water. Ist Observation. |
Having made sundry efforts, from time to time, to
discover, if ‘twere possible, the cause of the hotness or
power whereby pepper affects the tongue (more especially
because we find that even though pepper hath lain a
’ This observation indicates that the organisms were protozoa.
* Beyond the obvious fact that they were probably protozoa and bacteria,
I cannot offer any guess at the identity of the various organisms which L.
saw in sea-water.
132 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
whole year in vinegar, it yet retaineth its pungency); I
did now’ place anew about 3 ounce of whole pepper in
water,’ and set it in my closet, with no other design than
to soften the pepper, that I could the better study it.
This pepper having lain about three weeks in the water,
and on two several occasions snow-water having been
added thereto, because the water had evaporated away ;
by chance observing this water on the 24th April, 1676,
I saw therein, with great wonder, incredibly many very
little animalcules, of divers sorts; and among others,
some that were 3 or 4 times as long as broad, though
their whole thickness was not, in my judgement, much
thicker than one of the hairs wherewith the body of a
louse is beset.2 These creatures were provided with
exceeding short thin legs in front of the head (although
I can make out no head, I call this the head for the
reason that it always went in front during motion).
This supposed head looked as if ’twas cut off aslant, in
such fashion as if a line were drawn athwart through
two parallel lines, so as to make two angles, the one of
110 degrees, the other of 70 degrees. Close against the
hinder end of the body lay a bright pellet, and behind
this I judged the hindmost part of all was slightly cleft.
These animalcules are very odd in their motions, oft-times
tumbling all around sideways; and when I let the water
run off them, they turned themselves as round as a top,
and at the beginning of this motion changed their body
into an oval, and then, when the round motion ceased,
back again into their former length.’
cis Bi ate Fie i 5
! The exact date is not recorded ; but it will be seen from the next sentence
that the pepper was laid in water during the first few days of April, 1676.
® Unfortunately L. omits to state what kind of water he used. Had he
done so, it would have afforded some help in attempting to determine the
organisms which he found in it later.
* About 3. See p. 337 infra.
‘From the foregoing description I think it highly probable that the
animal observed was Bodo caudatus (Duj.) Stein,—one of the commonest
protozoa found in organic infusions. The description, as far as it goes, fits
this animal almost exactly.
LETTER 18. PEPPER-WATER 133
The second sort of animalcules consisted of a perfect
oval." They had no less nimble a motion than the
animalcules first described, but they were in much
greater numbers. And there was also a third sort, which
exceeded both the former sorts in number. These were
little animals with tails, like those that I’ve said were in
rain-water.”
The fourth sort of little animals,’ which drifted among
the three sorts aforesaid, were incredibly small; nay,
so small, in my sight, that I judged that even if 100 of
these very wee animals lay stretched out one against
another, they could not reach to the length of a grain of
coarse sand*; and if this be true, then ten hundred
thousand of these living creatures could scarce equal the
bulk of a coarse sand-grain.
I discovered yet a fifth sort,’ which had about the
thickness of the last-said animalcules, but which were
near twice as long.
2nd Observation [on Pepper-water].
The 26th of April,° I took 23 ounces of snow-water
(which was a good three years old, and which had stood
throughout either in my cellar or in my closet in a glass
bottle, well stoppered), wherein I was able to discover no
living creatures. Having poured this same water into a
porcelain tea-cup, with half an ounce of whole pepper, I
set it likewise in my closet. J examined this water every
day until May the 3rd, but could discover therein no
living creatures; and by now the water was so far
evaporated away and absorbed by the pepper, that some
* Perhaps a Cyclidiwm—equally common in infusions of all sorts.
* Vorticella sp. Cf. p. 118 supra.
* Evidently bacteria.
*T.’s “coarse sand-grain’’=approximately 355 inch in diameter. Cf.
p. 334 enfra.
> Probably bacilli. /
* i.e., anno 1676. le
(.
134 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
of the pepper-corns began to lie dry. And this water was
now so thick with particles, that you might almost
imagine you were looking at the spawn of very wee fish,
what time the fish discharges its roe, when the roe-corns
are very soft, and as ’twere hang together. Thereupon
I added snow-water to the pepper once more, until the
pepper-corns lay under about half an inch.
The 4th and 5th of May, examined it again, but
perceived no living creatures.
The 6th ditto, I discovered very many exceeding small
animalcules.' Their body seemed, to my eye, twice as
long as broad. Their motion was very slow, and oft-times
roundabout.
The 7th ditto, I saw the last-mentioned animalcules
in still greater numbers.
On the 10th ditto, I added more snow-water to the
pepper, because the water was again so diminished that
the pepper-corns began to lie dry.
The 13th and 14th ditto, the animalcules as before.
The 18th of May, the water was again so dried away,
that I added snow-water to it once more.
The 23rd of May, I discovered, besides the foresaid
animalcules, living creatures that were perfectly oval, like
plovers’ eggs.” I fancied that the head was placed at the
pointed end, which at times was stuck out a bit more.
Their body within was furnished with some 10, 12, or 14
globules, which lay separated from one another. When
I put these animalcules on a dry place, they then changed
" Probably bacilli.
® de Kievits eijeren gelijk MS. “like Cuckow-eggs”’ Phil. Trans. Kievit
means the Peewit or Lapwing (Vanellus cristatus), not the Cuckoo (Cuculus
canorus). The eggs of the former are, of course, those which are known
commercially as “ Plovers’ eggs”. The distinction is not without import-
ance here, as the “ Plover’s egg” is conspicuously pointed—that of the
Cuckoo being much more rounded.—The organism was probably Colpidium
or an allied ciliate. L.’s remarks a little later support the view that he was
observing the “small variety’ of C. colpoda—a very common inhabitant of
such infusions.
LETTER 18. PEPPER-WATER 135
their body into a perfect round, and thereupon oft-times
burst asunder; and the globules, together with some
watery humour, flowed out on all sides, without my being
able to discern any other remains. These globules, which,
in the bursting asunder, flowed apart from one another,
were of about the bigness of the first-mentioned very
little animalcules. And albeit I could as yet distinguish
no feet on the said animalcules, none the less I imagined
that they must be furnished with many very little ones ;
for the very smallest animalcules (whereof I have already
said there were a great many in this water, and of which
more than 100 sometimes lay around one of the little oval
creatures) were driven away from the bigger ones by the
motion which these made in the water (even when the
big animalcules themselves seemed to me simply to lie
still, without stirring at all), just as if you were to blow a
feather from your mouth.’ Of these oval animalcules I
could never discover any very little kind,’ how diligently
soever I sought them.
The 24th ditto, examining this water again, I found the
oval animalcules in a much greater number. Dvtto, in
the evening, looking again, I perceived so great a plenty
of the oval animalcules, that ‘twas not a mere thousand
that I saw in one drop; while there were several thousands
of the very small animalcules in the same drop.
The 25th ditto, I saw still more of the oval animalcules,
and some most exceeding thin little tubes,’ which I had
also seen many a time before this.
The 26th ditto, I saw such a great many of the oval
creatures, that I believe there were more than 6 or 8
thousand in one drop, not counting the multitude of very
little animalcules, whereof the number was far greater.
SS, - aE
1 This is obviously a description of a ciliate (e.g. Colpidium), with actively
vibrating cilia, lying among bacteria.
® f.e., any young ones.
* pijgpjes MS. Probably thread-bacteria.
136 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
But I took this water from the surface, and in the water
that I took from underneath there were nowhere near as
many. Seeing these little animals increase to so vast a
number, but therewithal not being able to detect that
they did wax in bigness, nor yet to espy any like creatures
drifting in the water, I bethought me whether these
animalcules might not well be put together in an instant
(so to speak) *: but this speculation I leave to others.”
The 26th dztto, in the evening, I perceived almost none
of the little animalcules; but I now saw divers creatures
with tails (whereof I have said heretofore that I saw ’em
in rain-water).” And furthermore I saw one animalcule
that was three times as long as broad. Through all the
water floated numberless particles, like thin little hairs
off men who haven’t been shaved for a fortnight*; but
with this difference, that many had a kink in them.
The 27th ditto, I perceived none at all of the very little
animalcules, but the large creatures in greater number.
The 28th ditto, almost all the animalcules in the pepper-
water were become somewhat scantier.’
The 80th dztto, I discovered very few animalcules in
the water, and I saw there now but one where some days
before I had seen a good hundred. And as the water was
' of deselvige niet wel in een moment des tijts (om soo te spreeken) en
waren te samen gestelt MS. He means that it crossed his mind that these
animals might possibly come into existence, on a sudden, by a fortuitous
concourse of inanimate particles in the water. As a rule, of course, L.
strongly opposed the doctrine of spontaneous generation.
* dog ik geef dit aen anderen over MS.
* i.e., Vorticella sp.
* By this quaint simile L. means to convey the idea that the particles, if
magnified in diameter to the size of human hairs, would be about as long,
in proportion, as those forming the beard of a normally clean-shaven man
who had not shaved himself for about a fortnight.
> wat dunder MS., lit. = somewhat thinner. I take L. to mean that the
water itself was now not so full of animalcules—not that the animalcules
had themselves grown thinner. But Oldenburg seems to have taken the
latter view, for he translates (Phil. Trans.) ‘all sorts of those living creatures
in this peppery water were grown thinner.” The ensuing paragraph supports
the above reading.
LETTER 18. PEPPER-WATER 137
now so dried away, that the pepper began again to he
above the surface, I filled up the tea-cup with snow-water
once more.
On June the Ist, the animalcules were again in as
great numbers as I had ever before seen, though I can’t
say that I saw any of the very little ones. But now I
could see very plain that the animalcules were furnished
with very thin little legs,* which was a very pretty sight
to see.
The same day, I discovered some few very little round
animalcules,’ that were about 8 times as big as the
smallest animalcules of all. These had so swift a
motion before the eye, as they darted among the others,
that ’tis not to be believed. The big creatures, which
were about 8 times smaller than the eye of a louse,’ were
in no less number.
My further observations on this water I have made no
note of.
8rd Observation [on Pepper-water].
On May the 26th, I took about $ of an ounce of whole
pepper, and pounded it small, and then put it in a
tea-cup in which there was about 22 ounces of rain-water,
stirring this water about in order that the pepper might
mix itself with the water and then sink to the bottom.
And after letting it stand thus an hour or two, I took
some of the forementioned water in which the whole
pepper lay, and which contained a multiplicity of little
animals, and mixed it with this water wherein the
pounded pepper had now lain for one or two hours: and
_
i.e., the cilia on the ciliates (? Colpidiwm).
* Probably larger bacteria.
* This is the first indication which L. gives of the size of his ciliates.
‘About 8 times smaller’? means “having a diameter of about a half”:
and this therefore agrees with the supposition that the “ oval animalcule”’
was the small species (or variety) of Colpidiwm so commonly found in
such infusions.
138 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
I observed that when I added rather much of the water
containing the pounded pepper, it came to pass that the
foresaid animalcules died forthwith; but when I added
somewhat less of the same water, then the little creatures
remained alive.
On June 2nd, in the forenoon, after I had made divers
observations since the 26th ultimo, but without being
able to discover any living creatures, I now saw a few
particles which had, indeed, the figure of some of the
little animals, although I could distinguish no life in
them, how attentively soever I looked. On the 2nd
again, at night, about 11 o’clock, I discovered a few very
little living animalcules.
The 3rd ditto, I discovered therein many more
animalcules, which were all very small, and about 2 or 8
times as long as broad.’ All through this water little
bubbles kept rising, as if ’twere fresh beer that stood
fermenting.
The 4th ditto, in the morning, I found therein a great
many animalcules. The same day, in the afternoon,
examining the water again, I saw such a great many
living creatures in one drop of it, that they amounted
to at least 8 or 10 thousand; and to my eye they were,
when viewed through my microscope, like ordinary
sand-grains to the naked eye.
On the 5th ditto, I discovered, besides the multifarious
very little animalcules aforesaid, some few (but not above
8 or 10 in one drop of water) little oval animals,” whereof
some exceeded the others quite 8 times in bigness,’ whilst
the biggest of them were in shape like the oval
animalcules that I have made mention of before (those
that were in the water wherein the whole pepper lay).*
* s00 lang als breet MS. “as broad as long” Phil. Trans.—an obvious
mistake.—The organisms were evidently bacilli.
* Probably Colpidium again.
* 1.e., were twice as long.
* i.e., they resembled the organisms previously identified as Colpidiwm.
LETTER 18. PEPPER-WATER 139
On the 6th ditto, the animalcules were as before.
On the 8th ditto, the little oval animals* were
multiplied, swimming among the foresaid very numerous
little animalcules*; and now they’ were very nearly all
of one and the same bigness.
The 9th of June, the oval animalcules were in yet
ereater number, but the very little animalcules were now
less. And now, using again a particular method in
observing, I saw the little feet or legs* (wherewith the
animalcules were provided underneath their body, which
was flat) moving very plainly ; and with such a swiftness,
that ’tis incredible. And methinks that ever and anon I
could make out that each of the globules, whereof, as I
have said, their body was for the most part composed,
was not perfectly round, but every one of them stuck out
in a point, in the same fashion as the shields or plates
on the sturgeon or thornback do.’ The said animalcules
were, to my eye, 8 times smaller than the eye of a louse.”
On the 10th ditto I took a little of the last-mentioned
water, and mixed it with a little water wherein 36 cloves
had now lain for about 3 weeks; and I perceived that,
no sooner did the multifarious little animals aforesaid
come into this mixed water, than they were dead.
On the 12th ditto, the said animalcules seen in no less
number; and as the water was now so evaporated away
and sucked up by the pepper, that the pepper itself began
* Colpidium.
* Bacteria.
*¢.e., the colpidia. L. cannot have meant that the ciliates and bacteria
were now equal in size.
‘ i.e., the cilia (on the Colpidium).
° ie., like the “ placoid scales ” of some Ganoid and Elasmobranch fishes,
such as the sturgeon (Acipenser) and the thornback (Raja clavata).
® This estimate accords with that given for the “ oval animalcules ’’ under
date June 1 (2nd observation).—Oldenburg’s translation in the Phil. Trans.
terminates at this point. All that follows has never previously appeared in
print.
140
1
2
8
LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
to lie dry, I threw the latter away, after first of all tasting
it on my tongue, and finding it as strong as if it had just
been pounded.
4th Observation {on Pepper-water |.
The 14th of June, a certain quantity of whole pepper
put in well-water.
The 16th dzttv, in the morning, on examining the same,
I discovered, in a tiny drop of water, incredibly many
very little animalcules, and these of divers sorts and sizes.’
My further observations I have not made note of, save
that on the 17th of July still more animalcules were seen,
and among them many of the little oval creatures” many
times mentioned already.
Examining the water again on July 20th, I now saw,
with very great wonder, that some very long and very
thin particles (which I imagine had come to my notice
in various waters before) were alive. These most
wonderful living creatures seemed, when viewed through
my microscope, thinner than a very fine hair of one’s
head, and about as long as the back of a bread-knife,°
others quite twice as long. Their whole body appeared
of one and the same thickness throughout, without my
being able to make out a head or any bodily parts; and
therewithal their body was very clear, and ’twas thus
very troublesome to succeed in seeing ’em alive in the
water. They moved with bendings, as an eel swims in
the water; only with this difference, that whereas an eel
always swims with its head in front, and never tail first,
Bacteria—various sorts.
Colpidiwm.
Another of L.’s homely similes. He means that the “animalcules”
were very long, and uniformly thin—their proportions being similar to those
of the blunt edge, or back, of a large knife such as is used for cutting bread ;
though their thickness actually appeared not so great, but even less than
that of a human hair as seen by the naked eye. Itis a peculiar comparison,
but on the whole conveys a tolerably accurate notion of the appearance of
the long thread-bacteria which he was evidently observing.
LETTER 18. PEPPER-WATER 141
yet these animalcules swam as well backwards as forwards,
though their motion was very slow. And were I to
contrast these creatures with the eels or worms which are
in vinegar,’ I imagine the proportions would be thus :
As a worm of the bigness of a big pin, is to an eel of
the thickness of one’s wrist : So are these very little living
creatures or eels in the pepper-water, to the size of the
eels in vinegar.
5th Observation [on Pepper-water].
On August the 2nd, in the evening about 7 o’clock, I
again examined my well-water, which was very clear
(especially when it stood in a kettle or pot; but standing
in a clean glass, alongside of clean rain-water, the rain-
water outdid the well-water in clearness). In this well-
water I saw living a great many of the oft-mentioned
very little animalcules*; some thousands, indeed, in one
drop of water. I then poured some of this water into a
porcelain tea-cup, adding thereto a quantity of coarsely
pounded pepper; and [I stirred round the pepper in the
water, deliberating whether the said animalcules would
remain alive in the peppery water, or whether they would
die. This water and pepper having been stirred up, I
examined it, and saw the animalcules living: after the
lapse of half an hour I examined it again, and saw the
animalcules still alive, but their motion was not so quick
as when they were in plain well-water. After the lapse
of two hours more, examining the water again, I saw the
ee ee
1 A yemarkably shrewd observation, which proves conclusively that L.
was here dealing with bacteria. The organisms were evidently the long
flexible thread-bacteria (Pseudospira C.D.) so common in infusions.
2 Of these more anon. The “vinegar-eel” (Anguzllula acett) was
described by L. in an earlier letter, dated 21 April 1676. See Phil. Trans.,
Vol. 0%, p: 6093 (1676). Power, Kircher, Borel, and others had, however,
discovered this organism at a still earlier date, though L. was apparently
unaware of their observations. IL. gives figures of the eel in a later letter
(No. 43, 5 Jan. 1685).
® fe., bacteria, in all probability.
142 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
animalcules even yet alive, though in much less number
than heretofore.
On the 3rd of August, about 7 o’clock in the morning, I
saw some few animalcules still alive; while the water was
fermenting, as if it had been beer that stood and worked.
In the afternoon, about 4 o’clock, examining it again, I
still saw a few animalcules alive. In the evening, at
about 9 o’clock, however, I saw very few animalcules
living.
On the 4th ditto, about 6 o’clock in the morning, I
could discover no living animalcules, how attentively
soever I looked; but I thought I saw some floating dead.
The evening of the same day, about 9 o’clock, I discovered
4 or 5 very little animalcules, and among them one some-
what bigger, and very round. Such an animalcule I have
never seen in well-water.
The 5th ditto, in the morning, I saw again 4 or 5 very
little animalcules, among them one that exceeded the
others a bit in length: and amidst the very many par-
ticles, I judged that I could distinguish little forms which
agreed in their shape with the foresaid living animalcules,
but I could discern no life in them. On the afternoon of
the same day, about 3 o’clock, I saw several most extra-
ordinarily small animalcules (nay, even smaller than
those in the well-water), together with many animalcules
that were somewhat bigger. These last * were well-nigh
round, and their motion was mostly all a-rolling, where-
withal they didn’t much hurry themselves. ‘Together
with these was a sort” that were of the same size, but
they were somewhat elliptical. And lastly, I also saw
some® (though very few) which were a good 20 times
bigger than the biggest sort spoken of above. These were
1 Probably small flagellates (? Monas sp.).
? Unidentifiable. Perhaps more elongated specimens of the same Monas.
* Perhaps Euplotes or an allied hypotrichous ciliate. (The movements
described indicate that it cannot have been a Cyclidiwm.) “ A good 20 times
bigger’? means “ having about thrice the diameter” of the former sort.
LETTER 18. PEPPER-WATER 1438
long, and bent crooked, the upper part of the body round,
but flat beneath, looking much after the fashion of an
s part of the peel of a large citron. Their motion was all
a-wallowing, on their back as well as on their belly. I
could discern no little feet or legs on them; and after this
time, moreover, I never saw them any more. In the
evening, about 10 o’clock, I saw the very little animal-
cules, and the round ones,” in much greater numbers;
together with a little animal that was 3 or 4 times as
long as broad *; and besides these, many little worms, or
little eels *, which were even smaller than the very tiny
eels spoken of before.
On the 6th ditto, about 6 o’clock in the morning, [
discovered a very great many (indeed, incredibly many)
exceeding little animalcules, to which, because of their
littleness, no shape can be given’; and with these a very
great number of round animalcules,’ which to my eye
seemed quite eight times as big as the first animalcules (in
which I have just said I could make out no shape). These
round animalcules I imagine to be more than 50 times
smaller than the eye of a louse. And besides these there
was a third sort,’ that were twice as long as broad, and
which had about the length of the round animalcules.
The fourth sort * was the very tiny eels; but now I could
not see their bending, when they moved, so very plainly
as I had seen it before: and at this time too I saw some
(though very few) animalcules, which had very nearly the
length of the eye of a louse, and which were in shape very
" Bacteria.
° 9? Monas sp.
* Unidentifiable; ? a small flagellate. (Had it been large, L. would
doubtless have supplied some further details.)
* Bacteria, probably Spzrzllwm sp.
> Bacteria.
° Larger bacteria ? (“8 times as big” = of twice the diameter.)
* Unidentifiable.
* Spirilla.
144
LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
much like (only much smaller) that animalcule which I
have previously likened to a piece of citron-peel. More-
over, I could not convince myself that I now saw, among
the sorts of animalcules described, those creatures which I
have said I saw in the well-water, although I examined the
well-water also.
The same day, about 3 o’clock in the afternoon, I saw
still more animalcules, both the round ones and those that
were twice as long as broad; and besides these, a sort
which were still smaller ; and also incredibly many of the
very little animalcules whose shape, this morning, I could
not make out. J now saw very plainly that these were
little eels,, or worms, lying all huddled up together and
wriggling; just as if you saw, with the naked eye, a
whole tubful of very little eels and water, with the
eels a-squirming among one another: and the whole
water seemed to be alive with these multifarious animal-
cules. This was for me, among all the marvels that I
have discovered in nature, the most marvellous of all; and
I must say, for my part, that no more pleasant sight has
ever yet come before my eye than these many thousands
of living creatures, seen all alive in a little drop of water,
moving among one another, each several creature having
its own proper motion: and even if I said that there were
a hundred thousand animalcules in one small drop of
water which I took from the surface, I should not err,
Others, seeing this, would reckon the number at quite
ten times as many, whereof I have instances; but I say
the least. My method for seeing the very smallest
animalcules, and the little eels, I do not impart to others ;
nor yet that for seeing very many animalcules all at once ;
but I keep that for myself alone.
The same day, about 11 at night, the animalcules were
as before. The sort in which I could hitherto discern no
shape, I now fancied to be round, rather than long.
* Spirilla.
LETTER 18. PEPPER-WATER 145
On the 7th ditto, about 8 o’clock in the morning, the
animalcules were as heretofore. The little eels or worms
were a bit bigger, but the very smallest animalcules I
could not now make out. Ditto, in the evening about
8 o’clock, I now saw again the smallest animalcules of
all, but few in number. The round animalcules very
plentiful; and the animalcules which were twice as
long as broad, together with the little eels, I saw in
numbers unspeakably vast, for the amount of water.
The 8th ditto, about 8 in the morning, the animalcules
as before. The same day, afternoon and evening, the
animalcules seen in no less number.
The 9th ditto, in the morning, the animalcules as
before. Ditto, in the afternoon, the animalcules in no
less number, excepting that the round animalcules
now seemed fewer to my eye.
Having been, from the 10th to the 17th of this month,
in Brabant and elsewhere for a holiday, I now observed
that the water was very small in amount, and thick
with all manner of very small particles; and I saw that
the animalcules lay alongside one another in great plenty,
without any motion, save 2 or 3 animalcules which I saw
moving feebly. Thereupon I again added a little well-
water to the pepper and the water that remained over:
and I then viewed the water, but notwithstanding could
perceive no further movement in it, after several
observations.
The 18th ditto, in the morning, examining this water
again, I saw the animalcules alive and moving in as
great numbers as ever heretofore, though their motion
was not so quick; excepting only the little eels, none of
which I could discern. Ditto, in the evening, the motion
in the animalcules was as quick as ever before.
The 19th ditto, the animalcules as before.
The 20th ditto, the animalcules as before.
The 21st ditto, the animalcules aforesaid, that were
almost round, were in incredibly great plenty, and more
10
146
LEEUWENHOEK AND HIS ‘“ LITTLE ANIMALS ’”’
than ever before; the animalcules that were twice as long
as broad were fewer in number than hitherto, and now I
could discern that before and behind they ran somewhat
to a point; and ’twas pretty to behold the motion, all
a-quivering and a-shivering, that such very little creatures
made in going forward. No others than these two sorts
could I discover. Among other particles, there drifted
through the liquid a multitude of short straight little
tubes, several times (yea, 3 or 4 times) shorter than
the foresaid very thin little eels or worms, so that they
were only to be made out by very curious inspection.
The 21st ditto, in the afternoon, the animalcules in
abundance, as before. The long animalcules are clear;
the rounded ones appear encircled with a dark streak, and
having at the hindmost part of their body a little dark
spot or point.
The 22nd ditto, the animalcules as before. The short
and very smali tubules were in greater numbers.
The 3rd of September, the animalcules being as before,
without my being able to espy any notable change in
them, I again poured well-water (in which there were
many living animalcules) upon the pepper, and at the
same time put also two eggspoonfuls of coarsely pounded
pepper into the water; considering whether the animal-
cules might not then die.
* (L have, moreover, well-water containing whole pepper
still standing in my closet; but I have sent no notes of
the observations made thereon. I have seen in it, besides
divers animalcules, a great many little eels or little
worms, together with a sort of little animals that were a
bit smaller than the oval creatures already oft-times
referred to. These were rounded like an oval at the hind
end of the body, but their foremost part had, at its end,
a crooked bend, like a parrot’s beak.”
*The whole of this passage is thus put in parenthesis in the MS., and
was perhaps meant for a footnote.
* Probably Chilodon.
LETTER 18. PEPPER-WATER 147
The animalcules which I have throughout called “ oval
animalcules”’, are not really oval, unless you look upon
them on the back or upper part of their body; and as the
making of observations is well-nigh a study in itself, I
have only just now exhibited them to myself very prettily
in side-view, and have demonstrated not only their little
feet, but also their head, and their very short and pointed
little tail. At such perfection in this tiny creature I did
creatly marvel’: and were it not that the multiplicity
of solid particles (which are present in plain water)
hindered me, I could describe the little animals even more
distinctly.)
The 4th of September, the animalcules were seen in
such great abundance as never before; but whether the
animalcules which were at first present in the well-water
were yet alive, I still can’t say for certain.
The 5th ditto, the animalcules in an incredible number,
much greater than hitherto; but they consisted of only
two sorts, to wit: the roundish animalcules, and the
animalcules that were twice as long as broad, albeit some
few somewhat exceeded the others in length. The long
animalcules were a bit thicker than the hair of a louse,
and the round ones about twice as thick.
The 6th ditto, the animalcules in as great abundance
as heretofore. I now imagined that the long animalcules
consisted of two sorts: and I imagined, furthermore, that
I saw animalcules of such extreme littleness as I had
never up to this date seen in pepper-water.
The 7th ditto, the animalcules in even greater number
than before this date.
The 8th of September, besides the foresaid long animal-
1T, was always carried away with delight at beholding the “ perfections ”’
of ‘little animals’’. So also, it appears, was his draughtsman: for L. tells
us elsewhere that in making drawings of a flea he was repeatedly provoked
to exclaim (his words being given by L. in large capitals) “‘ Lieve God wat
sijnder al wonderen in soo een kleyn schepsel!” (Letter 76, 15 Oct. 1693.)
Cf. also p. 279 znfra.
148
LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS ”’
cules and roundish animalcules, I discovered three which
had the figure of a pear, only with this difference, that on
the underside of their body they were flat.’ Such a sort I
had not seen till now in any water. And I had such a
hunt for these creatures, because they were so few, that I
gave no heed to the very smallest ones.
The 9th ditto, I perceived but one of the animalcules
that had the figure of a pear, in four several observations.
And though there was still quite a lot of water with the
pepper, yet I added more well-water to it, because the
pepper-water was become rather thick. Ditto, in the
afternoon, about 4 o’clock, I could see none at all of
the animalcules that had been in great plenty in the
well-water ere I poured it on the pepper; neither could
I discover any of the animalcules that had the figure
of a pear.
The 10th ditto, in the morning, the roundish and the
long animalcules were now in such inexpressibly great
crowds, that they far exceeded in number all the animal-
cules that I had ever seen up to this date in any waters.
Moreover, I could discern no other sort.
On the 14th ditto, I could remark no change since the
10th, save only that 1 now saw again animalcules which
had the figure of a pear; and I saw there besides an
animalcule with a tail.’
The 15th ditto, | saw more animalcules that had the
figure of a pear, and two or three animalcules with tails.
And I perceived at this time that the pear-shaped
animalcules kept not against the surface of the water,
like the other creatures, but that they swam a bit deeper
under water. Their thickness was about that of a single
small thread of a silk-worm,’ and they were about 13 times
’ Evidently a hypotrichous ciliate.
? t.e., Vorticella.
° Cf. Letter 146. 20 April 1702. To the Landgrave of Hesse. Printed
fully in Dutch and Latin collective editions.
LETTER 18. PEPPER-WATER 149
as long as broad. The smaller nearly round animalcules,
and the long ones, were present in no less number.
The 16th ditto, the animalcules that had the figure of
a pear, as before: the animalcules with tails were
increased to a greater number: the small round animal-
cules, and the animalcules that were twice as long as
broad, were now diminished in number.
* [The 16th ditto, the animalcules that had the figure
of a pear, as before: the animalcules with tails were even
more numerous than formerly: the long and the round
small animalcules were even more reduced in number. |
On this occasion I discovered three animalcules’ that
were equally thick throughout, but which tapered to
rounded ends before and behind, very like the fruit that
we call dates.* The thickness of them was about that of
a very fine sheep’s hair. Their motion was very curious,
with a rolling about and a tumbling and a drawing of
themselves together into a round.
The 17th ditto, the animalcules that had a figure like a
pear, as before: the animalcules with tails in greater
number: the long and the round animalcules were de-
creased still further, and therewithal very slow a-moving.
The animalcules that were equally thick throughout were
somewhat more plentiful; and now I could make out
"The passage here placed in square brackets is in the MS., but it is
obviously a repetition—with slight differences in wording—of the preceding
paragraph. lL. seems to have paraphrased the same entry in his notebook
(for Sept. 16) twice over, by mistake.
* Evidently a large ciliate—probably Oxytricha.
*dalen MS. I have been unable to find this word in any dictionary—
ancient or modern. Oldenburg (MS. ined.) translated the word thus, and
may have had some authority for so doing. Elsewhere, however, L. speaks
of the date by its usual Dutch name, dadel: cf. Letter 47, 12 Oct. 1685.
The description is consistent with the above rendering: and Dr E. P. Snijders
informs me that candied dates are still sometimes called “ confijte dalen”’,
in popular speech, in Holland.
‘ Blsewhere (Letter 80,2 Mar. 1694) L. shows that sheep’s wool consists
of a number of “ fine hairs” stuck together. By “a fine sheep’s hair’’ he
here means, apparently, one of these component filaments.
150
LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
that they were a bit flat in front, furnished with divers
little legs, which during motion stuck out a bit beyond
the body; and at the hind end of the body there was a
round spot, running out headwards in a dark streak,
looking very much like the guts or the blood in the
body of a louse,’ as seen with the naked eye.
The 19th of September, the numerous long and roundish
little animalcules were much slower in their motion, and
amany of them lay without any motion at all. The
animalcules with tails were increased to yet greater
numbers: the animalcules equally thick throughout, and
those that had the figure of a pear, were in number as
before.
My further observations I have not recorded: I can
only say this, that in the course of a day or two the
water again got so thick, that all the animalcules that
were still in it moved themselves very slow; and 2 or
3 days after I had poured in well-water once more, I
perceived the small animalcules in as vast a number as
ever heretofore.
[Observations on Vinegar. ]
For the last 2 or 3 years I have not been able to find
any little worms, or eels, in the vinegar that I keep in
a cask in my cellar, for my household. I now®* drew
off } pint of this vinegar into a glass, and set it in my
closet, covering it over with a paper to keep off the dust :
and after the lapse of 11 days, I did perceive therein
little eels, which multiplied from day to day. I have
divers times put a little vinegar into a little pepper-water,
and have always seen that as soon as the pepper-water
‘4 more particular description of this phenomenon was given by L. in
an earlier letter (7 April 1674) published—in part only—in Phil. Trans.,
Vol. IX, p. 23. The more famous description of the “blood and guts in the
louse” by Swammerdam was not published until long after this date.
* See note 2 on p. 141.
* No date is here recorded.
LETTER 18. VINEGAR Si
was mixed with the vinegar, the animalcules that were in
the pepper-water died instantly; albeit that I was unable
to perceive that the little eels, which were in the vinegar,
suffered any hurt from the pepper-water.
At another time I took some 10 parts of the pepper-
water last spoken of (at the time when the living creatures
were most plentiful in it), and added to it about 7 part 108
vinegar, containing living eels, or little worms. This
vinegar I put in at the bottom, and not on the surface, of
the pepper-water: and I took note that, the moment the
vinegar was added to the pepper-water, the multifarious
very little animalcules that were next the bottom, where
the vinegar was, lay without any motion; and those
animalcules lying further from the bottom became slower
in their motion; and after the lapse of a little while, all
the very little animalcules were dead: yet the motion of
the little eels was no less in this water than when they
were in the vinegar alone. This pepper-water and vinegar,
which together equalled in quantity one big drop of
water, I observed almost from day to day: and after the
lapse of about 2 or 3 weeks, I saw that the little eels in
this mixed water were greatly increased; for where at
first I had seen but 10 eels, I now saw fully 200 of ’em.
And among the rest I saw a great number of very little
eels, near of one and the same bigness as one another,
whose length, to my eye, equalled about 1 or t part of the
biggest eels of all; but notwithstanding the further ob-
servations that I made, I was able to discover no smaller
eels, nor yet any particles that looked like the foresaid
very little animalcules*; but they seemed all gone, without
any remains being left over. Seeing this multitude of
little eels (in the mixture of 10 parts pepper-water and
1 part vinegar), I imagined that surely they were not
Dee ———
1 Ags becomes evident later, L. means that he took 1 part of vinegar
to 10 parts of pepper-water—not, as he apparently says, one-tenth of a
part of the former to 10 parts of the latter.
2 = .
1.e., bacteria.
152 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
generated from any particles which might have been in
the pepper-water, nor yet from such as might have been
in the vinegar, as this, mixed with pepper-water, would
have become unfit for the production of living creatures :
but I felt firmly persuaded that the said little eels had
become thus increased by procreation. I then made use
of certain means, in order to throw more light on these
very little animalcules; and first of all, after I had broken
asunder or pulled apart some of the biggest sort (corre-
sponding to those that I had seen originally in my wine),
I saw that they were provided inside with a long structure,
which had about 4 of the thickness of the eel itself. I
imagined that this was the gut of the little animal. In
some, moreover, I saw still much thinner long structures,
which I imagined might well be small eels: otherwise
the body of this creature was very soft, and streamed
away on all sides in many big globules of various sorts,
and others that were very little (in proportion to the
animalcule). These globules did not consist of watery
matter, but were, in fact, oil: for just as clearly as you
can, by the eye, distinguish oil floating on water, from the
water itself, so clearly could I see the oily particles,
among which were some so small that they well-nigh
escaped the sight. These curiosities of mine I divers
times followed up further; and at last I saw very plainly,
among other things, that from an eel which I had broken
across the middle, there came out four distinct small eels,
each twisted on itself, very nice and pretty, and each
bigger than the one following: and the biggest, which
came out first, lay and lived, and wrenched itself loose,
and remained alive a little while." I have more than
once been able to see a small eel, out of an eel which I
* All these exact observations can be very easily confirmed. The vinegar-
eel is viviparous; and L. was evidently here dealing with large pregnant
females, whose larval young drop out and behave just as he says when they
are torn in two.—These were the first observations ever made on the
reproduction of Anguwillula.
LETTER 18. VINEGAR, GINGER-WATER 153
had broken in pieces, lie a-writhing, and remain alive so
long, that it wearied me to keep my eye upon it. I have
also seen two small living eels come forth from an eel
after I had cut it in pieces: and they moved themselves,
and swam, and were in bigness like the smallest sort. To
sum up, the more observations I made on this matter,
the clearer did I demonstrate that the small living eels
come out of eels: and I conceive also that ’tis certain
I have seen the little eels alive in the big eels; but this
came to my notice only when I had taken the big eels
out of the vinegar, and when they lay a-dying.’
[ Observations on Ginger-water. |
The 6th of May, 1676, I put into a porcelain tea-cup,
which holds a little more than 24 ounces of water, three
of the ordinary large pieces” of ginger, after I had first
of all bruised them a bit with a hammer; merely with
the idea of seeing if the snow-water which I poured on
the ginger would bring forth living creatures with it.
The 14th ditto. I observed this water almost every
day, but till now I could perceive no living animalcules ;
and by this time the water was so dried up, or drawn into
the ginger, that I poured fresh water upon it.
The 29th ditto, having again examined this water
almost from day to day since the 14th, I now discovered
* L. at this point enters upon a long digression (about one whole page),
in which he describes and discusses the structure of the peppercorns them-
selves and attempts to explain why they have a hot taste. This leads him
further to discuss the constitution of wheat and other kinds of grain, and
several physiological problems suggested by his observations. After this he
suddenly returns to his experiments with infusions, and at this point I have
resumed my translation. The observations here omitted have no interest
from a protistological standpoint.
* clawwen MS. UL. evidently means the broken pieces of the dried
rhizome of the plant, as commonly sold by apothecaries.—I am informed
that the irregularly branching pieces of rhizome are known in the trade as
“hands” of ginger: and I take it that L.’s “ claws” were the broken-off
“fingers” of such “ hands”’.
154 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
some very little animalcules, a bit longer and bigger than
the small animalcules seen by me in the pepper-water.
Nevertheless, these had a different form and motion;
for while the animalcules in the pepper-water went
forward all winding-wise, these animalcules all advanced
in jumps, hopping like a magpie: yet were they very
few in number.’
The 30th of May, observing the ginger-water anew, I
discovered at least 25 times more animalcules therein
than previously. Among them were some quite three
times as long as broad, and I fancied I saw that their
fore and hind ends were fashioned aslant:; that is, with
an acute angle and an obtuse angle, as I have said before”
of a like sort that were bigger. Ditto, about 10 o’clock
at night, the said animalcules seen in greater number.
The 31st ditto, the foresaid animalcules seen in still
much greater number, amounting to several thousand in
one drop of water: and some of them exceeded the others
in length.
The Ist of June, the animalcules seen in still greater
number.
The 3rd ditto, the animalcules seen in such a vast
number (in the water that I took from above, off the
surface of the water), that were I to declare, according to
my own judgement, how many thousands there were in
one drop of water, ’twould not be believable.
The 4th of June, the water was again so evaporated
away, that the bits of ginger began to lie dry; so I poured
on rain-water at this time.
The 10th ditto, upon the water lay a thick film, which
I took off: and I then saw some oval animalcules,* in size
and shape like those that I have said were in the pepper-
water.
" From the description of its jumping movements, this was probably a
Cyclidium—noted earlier.
” See p. 132, 1st observation on pepper-water. ? Bodo sp.
* Ciliates, but otherwise unidentifiable.
1
LETTER 18. GINGER- AND CLOVE-WATER 155
The llth ditto, the oval animalcules were in greater
number, mostly swimming at the top, against the thin
film that had come again over the water. On this
occasion I marvelled to see the violence that the first-
mentioned little living creatures’ exercised, whenever
they came out of the water on to a dry place, ere they
fell a-dying.
The 12th ditto, the oval animalcules were now in great
plenty, as well as the other animalcules: and because the
film that lay upon the water had grown in thickness, I
poured the water and ginger away.”
[Observations on Clove-water. |
On the 17th of May, 1676, I placed 36 cloves in some
24 ounces of rain-water, after I had first of all examined
the rain-water and found nought therein (so far as
animalcules are concerned), save a very few creatures
that were roundish, and which looked to my eye, through
my microscope, no bigger than a coarse sand-grain doth
to one’s naked eye.
The 25th of May. Up to this date I could perceive no
living creatures, notwithstanding the many observations
I had made since the 17th of this month. I now added
more rain-water (wherein I could discern no animalcules)
to the cloves.
The 12th of July. After I had made divers observa-
tions on this water, and between-times had filled up the
tea-cup with water once more; and having no thought
that I should discover living creatures in this water, so
i.e., those seen on May 29 (? Cyclidiwm).
? T. again digresses at this point in order to describe the structure of
the macerated ginger itself. After a long description and discussion—
occupying more than one whole page of the MS.—he returns to the subject
of animalcules, and at this point my translation is resumed. Nothing of
protozoological or bacteriological importance is contained in the lines which
I have omitted.
156
1
LEEUWENHOEK AND HIS “ LITTLE ANIMALS ’”’
that I did not examine it from day to day, and kept no
note of when I last added water thereunto: on this date
I discovered very many living creatures, which displayed
themselves, through my microscope, as no bigger than an
ordinary sand-grain to the naked eye. These were very
clear, and seemed to be about twice as long as broad.
Along with them were some few animalcules which looked
as big as ordinary ant-eggs’; the upper part of their body
being round and raised, the under part flat, like unto
tortoises in shape. ‘Their whole body seemed to be made
up of no other parts than big and little globules, which
were all very glittering, so long as the animalcules were
alive: but when I brought them into a dry place (where-
upon they oft-times burst asunder), the glittering went
off; and the globules became smaller, and flowed away
on all sides, together with some watery humour in which
these globules lay. These animalcules were provided
underneath the body with divers little legs, whereof 5 or 6
stuck out in front of the head during motion.
The 14th ditto, I discovered many more animalcules
than heretofore, but most of them were very small.
The 19th ditto, I discovered, besides the said creatures,
many animalcules with tails,” along with many long
animalcules that were fashioned aslant in front; and if I
saw aright, their hindmost part was somewhat cloven,
their body flat below and round above, their length well
anigh that of the little oval animals.
The 4th of August, I did not perceive the long
animalcules, but exceeding many very little animalcules,
and some few that were a bit bigger. The water being
now almost evaporated away, I added well-water to it.
i.e., they appeared, through the microscope, about as big as “ ant-eggs”’
appear to the naked eye. (In a later letter L. showed that the structures
commonly called “ ant-eggs’’ are not really the ova of the ant, but its pupae.
Cf. Letter 58, 9 Sept. 1687.) From the deseription which follows, they
were obviously hypotrichous ciliates: but it is impossible to identify them
more precisely.
* i.e., some species of Vorticella. Cf. p. 118.
LETTER 18. CLOVE-WATER Loh
The 8th ditto, I saw very many animalcules whose
figure was like an oval, and these were to my eye, through
my microscope, like coarse sand-grains to the naked eye;
and there were some few animalcules with tails; likewise
some little animalcules, and plenty that were bigger, and
had the length of the eye of a louse. These were bent a
bit crooked, the underneath part flat; and therewithal
looking much like an eighth part of a preserved citron-
peel. Their motion was all turning about, so that I am
persuaded that they had no little legs; and though they
were a bit smaller, they resembled very closely the little
animals previously likened to a piece of citron-peel. So
great was their number, that it did not amount to a mere
thousand or two in one drop.
The 17th of August, the animalcules found as before ;
but their motion was very slow: and as over a half of
this water was evaporated away, I added well-water to it
again.
The 18th ditto, the animalcules as before, and now
their motion was a bit quicker again; and I now saw
again more animalcules with tails.
The 20th ditto, the animalcules with tails were so
multiplied, that by now they were the most plentiful.
The 21st and 22nd ditto, the animalcules with tails
were now less, and their motion, too, was very slow.
Furthermore, these animalcules with tails, whenever they
got themselves stuck by the tail in any bit of dirt,
stretched ’emselves out somewhat longer than the
animalcules with tails which I have seen in pepper-
water. The little animalcules were now also less; and
here and there [ discovered one of the animalcules that
I have likened to an eighth of a citron-peel.
The 3rd September, I took one or two cloves out of the
water, and they were now become so soft that one could
rub them to bits between one’s fingers: and moreover, I
found but little savour in them. The animalcules were
now much decreased, and therefore, as the water was also
158
cc
LEEUWENHOEK AND HIS LITTLE ANIMALS ”
diminished, I poured in well-water, in which were living
animalcules. After the lapse of an hour, I examined this
water; and whereas I had seen before very few of the
animalcules inclining to an oval figure, I now saw many
of them, together with animalcules that were twice as
long as broad, besides the animalcules that were in the
well-water, and a very few animalcules with tails. I
added 8 fresh cloves to this water, wondering whether
the animalcules in it would then die.
The 4th of September, the animalcules as before,
saving that the animalcules with tails were so diminished,
that I descried but 2 or 3 of ’em.
The 5th ditto, the animalcules inclining to an oval
figure were in greater plenty; and I saw a few of those
that were twice as long as broad, but none of the animal-
cules that had been in the well-water, nor of the
animaleules with tails.
The 6th ditto, I perceived no other animalcules than
those tending to an oval.
The 7th of September, saw animalcules which inclined
to an oval, without being able to make out any other sort.
However, they were decreased rather than increased, and
their motion was not quicker, but rather slower.
The 8th of September, the motion of the animalcules
even slower, and they were no more plentiful.
The 9th ditto, in the morning, at 8 o’clock, the animal-
cules as before: and because the motion was so slow,
I added a little well-water. And in this well-water there
were many very little living animalcules. Dvtto, in the
afternoon, at 4 o’clock, I now saw the animalcules that
had been in the well-water still alive in plenty in this
clove-water; and the other animalcules were now moving
more lively. Ditto, in the evening at 8 o’clock, the
animalcules that had been living in the well-water were
now almost all of them dead; so that I was able to see
but 2 or 3 alive after several observations.
The 10th ditto, at 9 o’clock in the morning, no animal-
LETTER 18. CLOVE- AND NUTMEG-WATER 159
cules seen except those inclining to a round oval figure ;
but the motion of these was a bit nimbler, and they were
no less in number.
The 18th of September. The animalcules inclining to
a round oval figure are got less from day to day since the
10th of this month, so that at this time I was able to see
only a very few of them; but now I saw some extra-
ordinary tiny animalcules, which looked, through my
microscope, no bigger than common sand doth to the
naked eye.
The 19th ditto, stirring the water around a little, and
then examining it, I saw more of the animalcules likened
to a round oval than before this date. Along with them
I perceived the very little animalcules.
[Observations on Nutmeg-water. |
The 13th of July, 1676, I beat some big nutmegs in
pieces with a hammer, and put them in 24 ounces of
well-water. ‘This well-water I had divers times examined
during the summer till this date, but could yet discover
no living creatures in it, save now and then so few and
extraordinary small, that I did not see them till I had
made several observations.
The 17th ditto. Divers observations made since the
13th of the month, but no living creatures perceived
therein. And now the nutmegs lay on top, against the
surface of the water. The water itself lay fermenting, as
if it had been fresh beer: and betwixt the bits of nutmeg
lay a lot of round particles of oil, which were very supple.
These were for the most part 1000 times smaller’ than
a small sand-grain.
The 19th ditto, the fermentation was all done with, and
the nutmegs mostly sunken to the bottom.
ee
1 je., in bulk: or, in other words, they had a diameter of about one-
tenth of that of a small sand-grain—on L.’s scale, about one thousandth of
an inch, or 25.
160 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
The 24th of July, the water was for the most part dried
up. I again added well-water thereto; and in this well-
water there were now many very little living creatures,’
which, whenever the well-water came under the water
containing the nutmegs, died in a trice.
The 3rd of August. Made divers observations since
the last foregoing date, but discovered no living creatures
in this water till to-day. The creatures now seen’ were
very few, and so small, that they well-nigh escaped the
sight, notwithstanding that one had a very good micro-
scope. And as the water was, for the most part, dried
up again, and very many living creatures were at this
time present in all the common kinds of water, I poured
on some snow-water, in which there were no animalcules.
The 4th ditto, the animalcules as before; and they
moved among so many various particles, of very near the
same bigness as the animalcules themselves, that you
would say, ’twas no mere water in which the nutmegs
lay ; for twas made up of soft fluid particles stuck beside
one another, much as if you beheld, with your naked eye,
the spawn of frogs, or the seed of fishes when it is spent.’
The 5th ditto, I saw plenty of animalcules, which I
can’t call long, they looked to me to be round rather ;
for they were no bigger, through my microscope, than
very little sand-grains to one’s naked eye; and I must
say, that I deem them to be a good three or four times
smaller than the thickness of the hair of a mite, or one
of the little hairs wherewith the body of a louse is beset."
The 6th ditto, the animalcules as before.
The 7th ditto, I saw a huge number of exceeding
minute animalcules.
* Probably bacteria and monads.
* Bacteria.
? I, doubtless observed, on this occasion, bacterial “ zoogloea’”’ mixed
with particles derived from the macerated nutmegs.
‘ Cf. p. 337 infra. The very minute animalcules here mentioned were
undoubtedly bacteria.
LETTER 18. NUTMEG-WATER 161
The 17th ditto, I perceived no animalcules ; and as the
water was much evaporated away, I added well-water, for
want of snow-water.
The 18th ditto, no animalcules made out.
The 19th of August, many small animalcules seen
again.
The 20th ditto, the animalcules as before.
The 21st ditto, the small animalcules seen in greater
number. I likewise now saw some, though very few, that
were a bit bigger. These last were very nearly round,
only tending somewhat to an elliptical figure.
The 23rd ditto. Besides the said animalcules, I dis-
cerned, both now and yesterday, divers animalcules that
were twice as long as broad, running to a point before
and behind, and of the size of those in the pepper-water ;
but their motion was not so quivering. I fancied the
cause of this was that this water was thicker.
On the 3rd of September, I could perceive no animal-
cules. The water being now for the most part evaporated
away, I added well-water, wherein were very many little
animalcules. I also took a little bit of nutmeg out of the
water, and tasting it upon my tongue, found it was still
so strong that it surpassed many fresh nutmegs in savour.
The 4th ditto, the exceeding very little animalcules
now seen alive once more.
The 7th of September, the very little animalcules seen
alive, as before; yet could I discern no animalcules of
the sort that were in the well-water ere I put it to the
nutmegs. My further observations I have not writ
down.’
The objection hath divers times been urged against me,
that there are, hovering in the air, extraordinary small
living creatures, which are hid from our eyes, and can
" The record of observations ends at this point.
1a!
LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS”
only be discerned by means of surpassing good magni-
fying-glasses, or telescopes; and these creatures, they
say, have been seen in Rome.’ For my part, notwith-
standing the manifold observations I have carried out to
this end, I have as yet seen no lesser animalcules moving
in the air than those which are so big that you can
readily make them out with the naked eye. The very
little particles which I have commonly found in the air,
and which are there in motion, are all earthy particles,
which are given off by (so to speak) “ dustsome ” ’ things.
For you can’t tear a sheet of paper apieces, but what
more than a thousand very tiny fibres break off, and these
so light withal, that they can’t easily fall upon the earth,
owing to the motion that is in the air: you can’t draw a
comb through the hair of your head, but what various
very little particles, which lie or are stuck upon every
hair, are set loose and moved in the air; not to mention
the wearing away and the breaking off which each several
hair suffers in the act of combing. Nor can you so much
as rub your hands together, when they are dry, nor stroke
your face, without thereby imparting a multitude of tiny
scaled-off particles to the air; and ’tis even so with wood,
earth, smoke, etc. Such particles as these would seldom
fall upon the earth, so long as they be in the sun’s rays,
or in a light breeze; but on coming out of the sun’s rays,
and out of the strong motion of the air, they sink towards
the earth: and these little bits of dust thus lying still,
and not sticking to larger particles that are heavier, may
again be set a-moving by the mere motion of the air, or
the sun’s rays. From what observations I have made
hereon, I can’t say I ever saw, among the rest, two bits
of dust that exactly agreed with one another in shape.
But I'll not deny that there can be, in the air, any living
creatures which are so small as to escape our sight; I say
1
2
A rumour, I take it, of the imaginative work of Athanasius Kircher.
stofligte MS. lL. here invents a word meaning “ apt to form dust.”
LETTER 18. CONCLUSION 163
only that I haven’t descried them. And furthermore, I
am persuaded that they would not be able to remain alive
in the air, about our horizon; rather would they be
begotten in the clouds, where, in the continual dampness,
they could remain alive, and so be conveyed still living to
us in mist and rain. I fancy I have even seen something
of the sort in the early summer of this year, on two
several occasions, when there was a heavy mist here; but
I saw the supposed creatures without any motion. And
I believe I have now found out a means of performing
such observations more exactly and nicely in future.
These observations concerning living creatures, in the
liquors spoken of, were indeed deserving of closer atten-
tion and description ; but for that, there had been need
too of a whole man, which my circumstances did not allow
of: for I have employed only my spare time upon them.’
Much light is thrown on the observations recorded in the
foregoing letter by some of the Huygens correspondence. As
the relevant MSS. are now accessible in print, and as it would
take us too far afield to discuss the position of Huygens as
a protozoologist, I shall not now consider this correspondence
in detail. It is so important, however, that it cannot here be
ignored, and I therefore add the following notes by way of
supplement.
Christiaan Huygens never himself published any serious
contributions to protozoology: and the records of his own
observations, which were made in an attempt to repeat
Leeuwenhoek’s experiments, remained in manuscript and
unknown until only a few years ago. Consequently, his
private work” had no influence whatsoever upon the progress
' A few final remarks—having no bearing upon animalcules—are here
omitted.
* Published for the first time in Gwvres Compl. de Chr. Huygens: see
particularly Vol. VIII (1899), No. 2148, p. 122; and Vol. XIII, fase. ii
(1916), p. 698 sq. So far as I am aware, all that was previously known
about Huygens’s protozoological work is contained in the fragmentary notes
in his Opuscula Posthuma (1703) and Opera Reliqua (1728). These show
only that he was an imitator of L., and give no idea of the originality of
his own observations. There is also a reference to the subject in Gregory
(1713), however, while contemporary mention was made of his observations
in the Journ. d. Scav. for 1678.
ce
164 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
of protozoology. Had it been published in his lifetime, it would
have assured him a place in the very forefront of the founders
of the science. Even at the present moment the excellence
and originality of his observations have been largely obscured
by his modern editors. In my opinion most of the protozoa
described and roughly sketched by Huygens can be easily
recognized by any competent protozoologist, yet his editors
have not only failed to recognize the majority but have often
misidentified common species most ludicrously. As examples,
I may note that Huygens’s unmistakable account of Chilodon
(with figures, including a characteristic pair in conjugation)
is interpreted as “ probably infusoria of the genus Bursaria”’:
his description of Astasia, with its characteristic euglenoid
movements and “ hardly any colour”’, is said to suggest the
bright green and rigid Phacus—“ if having hardly any colour
be not taken to exclude a slight green coloration’: and so on.
But we are here concerned with Leeuwenhoek—not with
Huygens—so I shall say no more on this matter now. I
hope to deal with Huygens’s admirable observations on another
occasion.
Whilst Leeuwenhoek’s astonishing researches were being
considered by the Royal Society, he himself was continuing
them and was corresponding with Constantijn Huygens (pater)
about his discoveries. Sir Constantijn was also in frequent
communication with his son Christiaan, at Paris, to whom he
reported Leeuwenhoek’s findings. Christiaan, at first sceptical,
soon repeated and confirmed the experiments: and at the end
of 1678 he wrote a most interesting letter,’ accompanied by a
few sketches, to his elder brother Constantijn. In this letter
Christiaan gave unmistakable’ descriptions of Chzlodon,
Paramecium, Astasia, and Vorticella—all found in infusions:
and he added “I should much like to know what Leeuwenhoek
would say about all this, and whether he has seen anything
like them.” Evidently the letter was sent to Leeuwenhoek,
who wrote to Constantijn Huygens sen. about it a little later.’
" Chr. Huygens to Const. Huygens jun. 18 Nov. 1678. Printed in
Guvres Compl. Vol. VIII (1899), No. 2148, p. 122.
* To me they are all unmistakable in this description: and when the
notes of 26 July 1678 (published in Guvr. Compl. XIII (ii), 702) are also
taken into account, the identifications are surely beyond all doubt.
* Leeuwenhoek to Const. Huygens sen. 26 Dec. 1678. Letter printed in
Gwor. Compl. VIII, No. 2156, p. 140.
APPENDIX TO LETTER 18 165
Leeuwenhoek here says that he can recognize all the animal-
cules described by Christiaan, and notes where he had himself
observed them previously. But he makes one obvious though
natural mistake: he takes Huygens’s Astasia for the Dileptus
which he himself discovered, and on which he had observed
the cilia. Apart from this, Leeuwenhoek interpreted Huygens’s
protozoa conformably with my interpretations of his own.
Huygens observed not only the protozoa which Leeuwenhoek
discovered in pepper-water, but he also saw and delineated
(his fig. F.) the long thread-bacteria so commonly seen in
infusions. On these organisms Leeuwenhoek comments :
These long eels I have seen too. My wonder at these
animals, was because one was 3 or 4 times as long as
t’other, yet they were always of the very same thickness ;
and besides, they swam as well backwards as forwards,
without my being able to make out any head, or anything
that looked like a head. I have already written about all
this to the Royal Society at London’. :
This is an important passage, as it confirms what Leeuwen-
hoek had previously said about bacteria. A little later he
adds the following remarks, with which we may conclude this
first chapter in Protozoology :
All these animalcules aforesaid I found too in ordinary
water, though not so many by a long way as in pepper-
water. And in the summer, when I feel disposed to look
at all manner of little animals, I just take the water that
has been standing a few days in the leaden gutter up on
my roof, or the water out of stagnant shallow ditches:
and in this I discover marvellous creatures.
And whether I put in the water whole white pepper,
black pepper, coarse pounded pepper, or pepper pounded
as fine as flour, animalcules always turn up in it, even on
the coldest days in winter, provided only that the water
doesn’t get frozen.
This day [26 December 1678] there are in my pepper-
water some animalcules which I judge to be quite 8 times
* See p. 140 above.
166
cc
LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
smaller than fig. A.,* on which I can make out the paws
too, which are also pleasant to behold, because of their
swift motions. The paws of these animalcules are very
big, in proportion to their bodies.” Besides these animal-
cules, I discovered in pepper-water, some few weeks since,
yet others which I judge to be a good 1000 times less
than the animalcule in fig. A: for the circumference of
the whole body of one of these extreme small creatures is
no bigger than the thickness of a paw of the animalcule
in fig. A: and I am persuaded that thirty million of these
animalcules together wouldn’t take up as much room, or
be as big, as a coarse grain of sand.
Ajo ee ie Dee TR oy a ein oee DS a eee
' Referring to Huygens’s sketch of a small (and unrecognizable) ciliate.
> Ly. probably here refers to the cirrhi on a small hypotrichous ciliate
such as Huplotes.
167
CHAPTER 2
EPILOGUE TO LETTER 18. FURTHER OBSERVA-
TIONS ON THE FREE-LIVING PROTOZOA AND
BACTERIA
(LETTERS 19, 21, 23, 26, 29a, 30, 31, 32, 33, 71, 92, 96)
S we have already seen, Leeuwenhoek communicated his
A discovery of the Protozoa and Bacteria not only to the
Royal Society but also to Sir Constantijn Huygens.
The latter evidently wrote a reply—which is lost—to which
Leeuwenhoek rejoined, inter alia’:
In order to answer Your Excellency’s letter further, I
must yet wait 2 or 3 weeks, for the reason that I have to
repeat the observations I made some time since (concern-
ing the living creatures in water) with two kinds of
water, which, among others, I intend to study every day.
From these words it may be inferred that at the beginning
of 1677 Leeuwenhoek was still hard at work on his discoveries.
But the Royal Society also did not remain idle or disinterested :
the Fellows wanted to know more. Consequently, in an
editorial comment upon Leeuwenhoek’s observations on the
animalcules in pepper-water “—wherein he says that he saw
‘ several thousands of the very small animalcules”’ in a single
drop of liquid—Oldenburg remarks*: “ This Phaenomenon,
and some of the following ones seeming to be very extraordinary,
the Author hath been desired to acquaint us with his method of
observing, that others may confirm such Observations as these.”
"From Letter dated 15 February 1677. To Const. Huygens sen. The
original Dutch MS. is at Leyden, and has recently been printed in Zwvr.
Compl. de Chr. Huygens (1899), Vol. VIII, No. 2099, p. 21.
* See p. 135 supra, 2nd observation on pepper-water: 24 May 1676.
® Phil. Trans. (1677), Vol. XII, p. 829.
168 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
To Oldenburg’s inquiries Leeuwenhoek sent the following
characteristic reply’:
Your very welcome letters of the 12th and 22nd
ultimo” have reached me safely. I was glad to see that
Mr. Boyle* and Mr. Grew* sent me their remembrances :
please give these gentlemen, on my behalf, my most
respectful greetings. “T'was also a pleasure to me to see
that the other Philosophers’ liked my observations on
water, etc., though they found it hard to conceive of the
huge number of little animals present in even a single
"Letter 19. 23 March 1677. MS.Roy.Soc.—The greater part of this
letter was translated into English and published in Phil. Trans. (1677),
Vol. XII, No. 134, pp. 844-846. The original MS., in Dutch, is accompanied
by a MS. translation into Latin, concerning which L. makes the following
statement in a postscript (in Dutch, which I translate): “ Sir, seeing that
you are most times hard pressed to find time to translate my observations
into the English tongue, and mentioning this to a gentleman who hath
divers times been to visit me; this gentleman offered me his services, to
translate into Latin such of my observations as I may perchance com-
municate to you: which offer I did not decline, and I now send you his
Latin copy herewith, along with my own letter. I await your answer, and
would know if I can serve you by acting in this way in future.” Although
Oldenburg’s translation is said to be “ English’d out of Dutch’, it appears
to me almost certain—from comparison of the three versions—that the
English was really rendered from the Latin, and not from the Dutch copy.
My own translation—above—is from the latter, written in L.’s own hand.
This will explain several slight discrepancies between Oldenburg’s version
and mine. It must be added that L. himself also printed a considerable
extract from this letter, at a later date, in his Letter 96 (9 Nov. 1695)—
published in the Dutch and Latin works.
*7.e., February 1677.
*The Hon. Robert Boyle (1627-1691)—“ Father of Chemistry and
brother of the Earl of Cork.”
“Nehemiah Grew (1641-1712), to whom several of L.’s most interesting
letters were addressed, was a Doctor of Medicine (Leyden, 1671) and
Secretary of the Royal Society from 1677 to 1679. He was educated at
Pembroke Hall, Cambridge, and became a Fellow of the Society in 1671:
but he is best known for his botanical work, and his catalogue of the
Society's museum. As a botanist he was the rival of Malpighi, and a
pioneer in the study of vegetable morphology. His later work is deeply
tinctured with religion. (His father, Obadiah Grew, was an ejected
minister of the English Church.) For his biography see the Dict. Nat.
Biogr. and Arber (1913).
*de Heeren Philosophen MS.—i.e., the Fellows of the Royal Society.
LETTER 19. 23 mMARCH 1677 169
drop of water. Yet I can’t wonder at it, since ’tis
difficult to comprehend such things without getting a
sight of ’em.
But I have never affirmed, that the animals in water
were present in such-and-such a number: I always say,
that I imagine I see so many.
My division of the water, and my counting of the
animalcules, are done after this fashion. I suppose that
a drop of water doth equal a green pea in bigness;* and
I take a very small quantity of water, which I cause to
take on a round figure, of very near the same size as a
millet-seed. ‘This latter quantity of water I figure to
myself to be the one-hundredth part of the foresaid drop :
4s for I reckon that if the diameter of a millet-seed
45° be taken as 1, then the diameter of a green
225 -pea must be quite 43. This being so, then a
_— + quantity of water of the bigness of a millet-seed
20m”, maketh very nearly the sz part of a drop, ac-
cording to the received rules of mathematicks
00 ©. (8.-« Shown. in the margin). This amount of
~ 91] Bas water, as big as a millet-seed, I introduce into
a clean little glass tube (whenever I wish to
millet-seeds
equalone let some curious person or other look at it).
Sie This slender little glass tube, containing the
(vobmme)- “water, I divide again into 25 or 30, or more,
parts; and I then bring it before my microscope, by
means of two silver or copper springs, which I have
attached thereto for this purpose, so as to be able to
place the little glass tube before my microscope in any
desired position, and to be able to push it up or down
according as I think fit.
I showed the foresaid animalcules to a certain
Gentleman, among others, in the manner just described ;
and he judged that he saw, in the zoth part of a quantity
'In Letter 96, L. tells us that his standard “ green pea”’ weighed 8 grains.
See p. 214 infra.
170
LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
of water as big as a millet-seed, more than 1000 living
creatures. This same Gentleman beheld this sight with
ereat wonder, and all the more because I told him that
in this very water there were yet 2 or 3 sorts of even
much smaller creatures that were not revealed to his
eyes, but which I could see by means of other glasses
and a different method (which I keep for myself alone).
Now supposing that this Gentleman really saw 1000
animalcules in a particle of water but soth of the bigness
of a millet-seed, that would be 30000 living
Shoe creatures in a quantity of water as big as a
9730000 +4+%millet-seed, and consequently 2730000 living
creatures in one drop of water. Otherwise, I
imagine the quantity of water to be of the bigness of a
coarse sand-grain; and in this quantity I imagine that
I see upwards of 1000 living creatures. Now I take it
that the bigness of a coarse grain of sand beareth the
following proportion to a drop of water: If the diameter
of a sand-grain be 1, then that of a drop of water is more
than 10, and consequently a drop of water is more than
1000 times bigger than a sand-erain. ‘Thus there are
more than a thousand times a thousand living creatures
in a drop of water. Tis in such a fashion that I make
my uncertain and imaginary reckoning of the animalcules
in water: but I guard myself, so far as ‘tis possible,
against making the number too big, as you can see from
the foregoing lines of my letter, wherein I have made
the number not half so big as others well might do.
My counting is always as uncertain as that of folks
who, when they see a big flock of sheep being driven,
say, by merely casting their eye upon them, how many
sheep there be in the whole flock. In order to do this
with the greatest exactness, you have to imagine that the
sheep are running alongside one another, so that the flock
has a breadth of a certain number: then you multiply
this by the number which you likewise imagine to make
up the length, and so you estimate the size of the whole
LETTER 19. METHOD OF OBSERVING lg
flock of sheep. And just as the supposed number may
differ from the true number by fully 100, 150, or even 200,
in a flock of 600 sheep, so may I be even more out of my
reckoning in the case of these very little animalcules: for
the smallest sort of animalcules,’ which come daily to my
view, I conceive to be more than 25 times smaller than
one of those blood-globules which make the blood red 5
because I judge that if I take the diameter of one of
these small animalcules as 1, then the diameter of a
blood-globule is at least 3.
These, Sir, are the trifling observations which I have
shown to divers curious persons, to their great satisfaction ;
but the other things that I have seen, and my particular
microscope, I cannot yet resolve to make public: which
I beg you, Sir, and your fellow philosophers, not to take
amiss.
Since sending off my letter” concerning the little
animals in water, I’ve not remained idle; but I have con-
tinued to examine divers sorts of water, examining even
that which was distilled or boiled. During the last sharp
spell of cold, when all the little animals had perished, I let
the water thaw by the fire; and when it had stood a whole
day in my bedchamber, with the fire kindled all the time, I
saw, after the lapse of 24 hours (and at another time after
17 hours), that living creatures had come again in the
water. Upon this subject I might, indeed, say something
further; but I note that my former letter is still under
your consideration, so I will spare you more.
To give your Philosophers further assurance, con-
cerning the reality of the multifarious living creatures in
even only a very little quantity of water, ‘tis my intention,
when they appear again in great plenty in the water, to
obtain testimony thereof, which I shall then send you.
The foregoing Letter was read at the meeting of the Royal
Society on 5 April 1677 [O.S.]; and the observations excited
‘7.e., Bacteria.
? Referring to Letter 18 (p. 117 swpra).
ie LEEUWENHOEK AND HIS ‘“ LITTLE ANIMALS ’”’
so much interest that the Secretary (Nehemiah Grew) was
ordered to repeat Leeuwenhoek’s experiments, for the greater
satisfaction of the Fellows.’
In a further communication on the same subject—and
various others—Leeuwenhoek fulfilled his promise to send
the testimony of divers credible eye-witnesses in support of the
truth of his statements. To a modern worker it seems some-
what curious that a scientific observer should think of calling
in such people as notaries public and ministers of religion to
vouch for the accuracy of his observations: but Leeuwenhoek
could think of no better method of establishing his bona fides,
and the result was, no doubt, satisfactory to all parties con-
cerned. It should be remembered that Leeuwenhoek’s
reputation was not yet firmly established at this early stage in
his scientific career, and we know that certain people had
already expressed their doubts as to the accuracy of his
observations. Among them was Christiaan Huygens, who,
writing to Oldenburg in 1675, says: “I should greatly like to
know how much credence our Mr Leeuwenhoek’s observations
obtain among you. He resolves everything into little
globules; but for my own part, after vainly trying to see some
of the things which he sees, I much misdoubt me whether
they be not illusions of his sight ; especially when he professes
to discover the particles whereof water, wine, and other
liquors, are composed.” It was this scepticism regarding
his researches, apparently, which caused Leeuwenhoek to
send those long and detailed extracts from his note-book—
which, as already noted, are peculiar to his 18th Letter—to
the Royal Society. The disbelievers, therefore, did a signal
service to posterity; for they put Leeuwenhoek on his mettle,
"Cf. Birch, Vol. III, p.338: “It was ordered, that Dr. Grew should be
desired to try what he could observe in the like waters; and that for this
purpose an extract should be given him by Mr. Oldenburg of Mr.
Leewenhoeck’s observations formerly read to the Society.”
* Huygens to Oldenburg ; 30 January 1675. MS.Roy.Soc. This letter
has lately been published in (uur. Compl. de Chr. Huygens, Vol. VII,
No. 2003, p.399. The original is in French, and the above is my
translation of the passage in question—-Huygens was mistaken in
supposing that L. laid claim to having detected the particles (molecules)
of which water and other liquids consist—as is abundantly proved by L.’s
own statements: see, for example, his letter to Const. Huygens (20 May
1679) translated on p. 187 infra.
LETTER 21. 5 OCTOBER 1677 iV (e:
and thereby enabled us to read today a detailed record of some
of the most remarkable and original researches ever executed.
The further communication referred to above is
Leeuwenhoek’s 21st Letter—according to my reckoning—
and the passages in question are as follows’:
In my letter of 23 March, 1677, I demonstrated that
one drop of water (which is as big as a green pea) is
equal in volume to 92%” millet-seeds: and to bring it
home to some friends of mine who could not grasp this,
I took 6 millet-seeds and stuck them alongside one
another with a little pitch. Then, with a pair of callipers,
I took the width of the axes of the said millet *-seeds, and
found the distance between the points was equal to the
axis of a big currant; and I remarked that the cube of 6
is 216. Now, said I, let us put an uncertain for a certain
quantity; and let us say, that as the currant sinks in
water, and the millet-seeds sink likewise in water, they
are therefore of like gravity: this being so, then 216
millet-seeds should weigh as heavy as this currant. I
then placed the currant in a small but exceeding nice
pair of scales, and found that 212 millet-seeds were of
equal weight with the currant.
I said also* that when I should again have a great
number of living creatures in water, I would send you
testimonials thereof, for the satisfaction of yourself and
the other Philosophers: these I now send you herewith,
from eight several Gentlemen, some of whom say that
nn
"From Letter 21. 5 October 1677. To Oldenburg. MS.Roy.Soe.
An English abstract was published by R. Hooke in his Lectures and
Collections (1678), Part II; Letter I, pp. 81-83. (Also reprinted in Hooke’s
Lectiones Cutlerianae, 1679.) Apparently this letter, though sent to
Oldenburg, came into Hooke’s hands when he succeeded him—after his
death—as Secretary of the Society.—This letter is called “ [26] Brief 18B”’
by Vandevelde (1922, p.356), who, as he was unaware of the existence of
the original MS., could assign no date to it. My translation is made from
the manuscript itself.
? This is a mistake. It should be 91 (91°125). See p. 169 supra.
® In the MS. the word geerst (= millet) is here miswritten “ geest’’.
* 7.e., in his letter of 23 March 1677. See p. 171 supra.
174 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS ”
they have seen 10,000 living creatures in a parcel of
water the bigness of a millet-seed, while others say
80,000 and also 45,000. I have generally counselled
these Gentlemen, when giving their testimony, to put
down but half the number that they judged they had
seen; for the reason that the number of animalcules in
so small a quantity of water would else be so big, that
’twould not be credited: and when I stated in my letter
of 9 October, 1676, that there were upwards of 1,000,000
living creatures in one drop of pepper-water, I might with
truth have put the number at eight times as many. For
if there be, as the testimonial saith, 45,000 animalcules in
a quantity of water as big as a millet-seed, then
3? there would be 4,140,000 living creatures in a
50000 Crop of water: and over and above this vast
4050000 number, I cau say that I am able to discern at
4140000 times even as many other living creatures, which
are so little that they were hid from the sight
of the Gentlemen who gave their testimony. ‘The first
number, when doubled, amounts therefore to 8,280,000
living creatures in one drop of water. This is incon-
ceivable: but let us put it thus, that supposing a coarse
grain of sand be divided into 8,000,000 parts, then I do
indeed see little living creatures in water which are no
bigger than these particles of sand would be. And this
being conceived, ’twill not appear so marvellous.
The attestations' of the eight eye-witnesses have for-
tunately been preserved with the foregoing letter. There are
actually five of them, but one bears three signatures and
another two—making eight testimonies in all. One® is in
1 Presented at a meeting of the Society on 15 October 1677, and read on
November 1 [0.8.]. Cf. Birch, Vol. III, pp. 346, 347.
? By Alexander Petrie, son of a more famous father of the same name
(ca.1594-1662) who was a Scottish divine and minister of the Scottish
church at Rotterdam. The father’s life will be found in Dict. Nat. Biogr.,
but I have been unable to discover anything further about the son—the
present writer.
THE ATTESTATIONS 175
English, and is written and signed by the minister of the
English church at Delft. It is as follows’:
I underwritten, being willing to give testimony unto
that whereof I was an eye-witnesse, do declare that having
seen and read Mr Leewenhoecks letter of March 23. 1677.
as it is set down in the printed Philosophical Transactions,
Numb. 134. p. 844. I was desirous to see a proof of
what I found there related; and for my satisfaction, Mr
Leewenhoeck did put a litle quantity of water, about the
bignesse of a Millet-grain, into a very slender glasse-pipe,
on which looking through his Microscope, I did see a
very great number of litle animals moving in that water,
so many that I could not possibly number them, and to
my sight they seemed to exceed the number expressed in
his fore-mentioned letter: and moreover, being desirous
to see a proof whether those animalcula were indeed
living animals, Mr Leewenhoeck by adding a very small
quantity of vinegar to the same water, and putting it
again into the same glasse-pipe, I did see those litle
animals in the water, but they did not moove at all (being
killed by the vinegar) which I beheld with admiration,
that in so small a quantity of water I should see such a
vast number of those litle animals. Whereof, being
Testis oculatus, I was willing at the desire of ingenious
Mr Leewenhoeck to confirm the truth of his relation by
this testimony written and subscribed by me, in Delft,
Aug: =a HORT:
Alex: Petrie.
Pastor of the English Congregation in Delft.
The other testimonials are couched in similar terms. There
is a long one in Latin, signed by “ Benedictus Haan’ Pastor
* MS. Roy. Soe.
2 Benedictus Haan (sew de Haan) was Lutheran minister successively at
Breda (1666), Delft (1675), and Amsterdam (1692). He died in 1702, and
is otherwise dimly remembered as the author of sundry verses which,
according to van der Aa, afford very feeble proof of his ability as a poet.”
cc
176 LEEUWENHOEK AND HIS “ LITTLE ANIMALS
Luther: Delph:” and ‘ M. Henricus Cordes’ Past. Luth.
Hag.’ ; and there are two shorter ones in the same language
signed respectively by “ R. Gordon’ Medicinae Studiosus”’ and
the three following persons: “J. Boogert* J.U.L. et Notar.
Publ.” ; ‘“ Rob. Poitevin * Doct. m. monspel.” ; ‘“‘ W. V. Burch °
J.U.L. et coram curia Hollandiae advt.” The remaining
attestation is short and in Dutch, and is signed ‘“ Aldert
Hodenpijl.”’°
* Hendrik Cordes, Lutheran minister at The Hague from 1674 to 1678,
was the son of Paulus Cordes (1613-1674), who held a like office at
Amsterdam. Hendrik, who died in 1678, is known to students of Spinoza:
for his successor was the Colerus (Kéhler) who wrote the life of the Jewish
philosopher. Colerus (1705), speaking of Spinoza, says: “He had a great
esteem for Dr. Cordes, my Predecessor; who was a learned and good
natured Man, and of an exemplary Life, which gave occasion to Spinosa
to praise him very often. Nay, he went sometimes to hear him preach,
and he esteem’d particularly his learned way of explaining the Scripture,
and the solid applications he made of it. He advised at the same time his
Landlord and the People of the House, not to miss any Sermon of so
excellent a Preacher.” See Pollock (1899) p. 395.
*This was Sir Robert Gordon (1647-1704), who “travelled much into
foreign countries for his improvement, was a man of extensive learning and
knowledge, and particularly skilled in mechanics and chemistry.’’ He was
son of Sir Ludoyick Gordon, of Gordonstoun, Elginshire, and became a
Fellow of the Royal Society in 1686. (Cf. Birch, Vol. IV, pp. 454, 455.)
Owing to his scientific pursuits he became known in the neighbourhood
where he lived as “ Sir Robert the Warlock”. For his life see the Dict.
Nat. Biogr.
*J. Boogert. The letters J.U.L. stand for Juris Utriusque Licentiatus—
a degree inferior to that of Doctor. It is evident, therefore, that he was a
lawyer and notary public; and Mr Bouricius tells me further that his
forename was Johannes and he was the son of a physician. It is probable
that he was the Jan Fransz. Boogert (or Bogaert) mentioned in Boitet
(1729, pp. 453, 495) as one of the governors of the reformatory at Delft in
1677, and a governor of the poor-house in 1680. This J. B. died in 1702.
‘Robert Poitevin, Doct[or] m[edicinae] Monspell[liensis], I cannot
trace further: but I find that several other medical men with the same
surname also qualified at Montpellier, where other members of this family
resided. Perhaps he was the Leeuwenhoeks’ family physician. Astruc
(1767) makes no reference to him.
°W. vlan der] Burch. The words following his name show that he
was a barrister; and I think he must have been the Willem Reyersz. v. d.
Burch (1627-1712), sometime town-councillor and “ weesmeester”’ at Delft,
who is referred to in Boitet (1729, p.90 et alibi)—though Mr Bouricius
(in litt.) considers this doubtful.
*Aldert Hodenpijl. Mr Bouricius informs me that he was married to
TESTES OCULATI ney
All these attestations bear out what Leeuwenhoek himself
tells us in his letters. But they also tell us that the capillary
glass tube containing the animalcules was as thick as a horse-
hair * (Haan and Cordes), and that it was divided into a large
number of measured parts, though it contained but a droplet
of water no bigger than a millet-seed. Hodenpijl says the
animalcules looked to him as large as lice, or even larger’:
while Haan and Cordes declare that some of them appeared
as big as bugs."
To the testimony of these worthy men we may now add
that of Christiaan Huygens, who, at the end of his French
version of Leeuwenhoek’s observations,’ added the following
remarks of his own’: “These are the observations of Mr.
Leeuwenhoek. His manner of making them is to introduce
the water into very little glass tubes, one third or one quarter
of a line in diameter; and these he afterwards applies to his
microscopes. He showed me some of these little insects very
distinctly, continually tumbling about in the water”. We
may suppose, accordingly, that Huygens, when he wrote this,
had overcome his original scepticism regarding Leeuwenhoek’s
observations. Indeed, the demonstration of which he here
speaks was probably the stimulus which prompted him, soon
Judith le Roy, and he has found records of the baptism of three of their
children (circiter 1668): but he has been able to find out nothing of present
interest about him in the Archives of Delft. It seems probable, however,
that Aldert H. is identical with Aalbert H. who is recorded in Boitet (1729,
pp. 519-20) as having been schutterkoning (= champion shot) of Delft in
1661, 1665, and 1668. (The discrepancy between ‘‘ Aldert ”’ and “ Aalbert”
may be easily accounted for—Mr Bouricius assures me—by the “ general
slovenliness [slordigheid] in writing names at that time”.) Why L. sent
his testimony I do not know—unless it was because his pre-eminence in
shooting guaranteed the excellence of his eyesight.
‘ad crassitiem pili equini crasso MS.
* Haan and Cordes say 50 parts, Hodenpijl says 70, and Boogert and his
co-signatories say 90. No doubt the discrepancy is to be explained by the
circumstance that they recorded L.’s procedure on three different occasions.
* hebbende de groote van een luijs, en sommige grooter MS.
*apparebant ad magnitudinem cinvicis MS.
> See p. 115, note 6.
° Published in Guvr. Compl. de Chr. Huygens, Vol. VIII, p. 27. These
remarks remained in manuscript until 1899, when this volume was published.
The original is in French, and the above is my translation.
12
178 LEEUWENHOEK AND HIS “LITTLE ANIMALS ”’
afterwards, to make his own remarkable contributions to
protozoology.:
It cannot be doubted that the “ very smallest animalcules,”’
of which Leeuwenhoek himself speaks, were in reality not
protozoa but bacteria. The particulars which he records prove
this conclusively, and it is hardly necessary to make infusions
of pepper—as I have done*—to convince oneself of this:
while the fact becomes superabundantly clear from Leeuwen-
hoek’s next letter on this subject, which was written at the
beginning of 1678 and contains the following remarkable
passage *:
I can't help mentioning that I can now make out, very
plain and clear, the shape of those little animals of the
smallest sort, whereof I said before* that I could ascribe
no figure to them ; and this because of the pleasure that
I do take in their manifold delightful structures, and the
motions that they make from time to time in the water.
Upon the 4th of this present month,’ when it froze hard,
I did fill a small clean glass with pounded pepper to 3 of
its height, adding § of rain-water, and set it for the first
night in my bedchamber. The next day, it’ being well
softened, I put it’ in my closet; and within thrice 24
" See p. 163 supra.
? Cf. also Beijerinck (1913).
* From Letter 23,14 January 1678. This letter was written to Robert
Hooke, who published an incomplete English version of it in his Lectures
and Collections (1678), Part II; Letter 2, pp. 84-89. This translation was
made by Hooke himself: for in a letter to L., dated 10 March 1682 (MS.
unpublished), he says so, and adds: “I have as neere as I could followed
the sense of your Expressions though not verbatim.’’—I translate from the
original MS. I may add that this letter serves to confirm my numeration
of L.’s early epistles: for it is No. 23 according to my reckoning, and L.
himself refers to it in his 113th Letter as “my 23rd”. It was read at a
meeting of the Society on 24 Jan. 1678 (cf. Birch, III, 380), but is not to be
found in the Phil. Trans., nor in the Dutch or Latin editions of the letters.
Hooke reprinted his translation in Lectiones Cutlerianae, Part V (1679).
* Letter 18. (Seep. 143 supra.) The organisms referred to were evidently
bacilli.
° January, 1678.
® ¢.e., the pepper.
” i.e., the glass.
LETTER 23. 14 JANUARY 1678 179
hours I discovered in it’ so great a many of such incon-
ceivably small creatures, that a man’s mind may not
contain them all: and in my judgement, the sort that
were most plentiful were much more than 1000 times
thinner than a hair of one’s head, and 3 or 4 times as
long as thick. These would oft-times shoot so swiftly
forward with the hindmost part of their body, that you
might think you saw a pike darting through the water ;
yet each shoot was, in length, most-times about half a
hair’s breadth. ‘The figures of the other sorts of creatures,
whereof some were even less, I shall pass over, else
’twould take all too long a-writing: I will only say, that
in pepper-water, that hath stood somewhat long, I have
oft-times seen, among the extraordinary little animalcules,
little eels;? and the structure and the motions which
these had, was as perfect as in big eels. But they were,
to my eye, quite a thousand times thinner than a hair off
one’s head ; and if a hundred of these little eels were laid
out end to end, the whole length of them would not reach
to the length of a full-grown one of those eels that are in
vinegar.*
Leeuwenhoek’s next letter in which we find any mention
of protozoa was written in September of the same year (1678).
It also contains some observations of whose precise signifi-
cance I am uncertain: but it is so characteristic, and so
clearly reveals his method of working and ways of thinking,
that I cannot refrain from quoting it. This is what he there
Says’:
’ i.e., the pepper-infusion in the glass.
* Spirilla.
® Anguillula aceti—the “ vinegar-eel’’—which L. regarded as really a
little fish. Large specimens measure about 1:5 mm. in length: ef.
p. 335 infra.
“ From Letter 26. 27 September 1678. To Nehemiah Grew. MS.Roy.Soc.
Unpublished. (A poor contemporary English MS. translation accompanies
the original Dutch MS.) The above is my translation of a part of the
letter.—There is an important reference to this epistle in L.’s letters to
Magliabechi (vide Targioni-Tozzetti, 1745: Epist.I, Vol. II, p. 345); but
the observations on the reddening of grass are there referred to the year
1648—which must assuredly be a misreading or misprint for 1678.
180
“ce
LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
But many of the things we imagine, and the natural
objects that we inquire into, are very insignificant ; and
especially so, when we see those little living animals
whose paws we can distinguish, and estimate that they
are more than ten thousand times thinner than a hair of
our beard; but I see, besides these, other living animal-
cules which are yet more than a hundred times less, and
on which I can make out no paws, though from their
structure and the motion of their body I am persuaded
that they too are furnished with paws withal: and if
their paws be proportioned to their body, like those of the
bigger creatures, upon which I can see the paws, then,
taking their measure at but a hundred times less, it
follows that a million of their paws together make up but
the thickness of a hair of my beard; while these paws,
besides their organs for motion, must also be furnished
with vessels whereby nourishment must pass through
them.
Because many people, both in the towns and in the
open country, are stricken with fever,’ and because their
shoes get very red whenever they walk through the grass
in the meadows; the common man concludes that the air
is therefore infected, and very fiery. This coming to my
ears, I betook myself without the town and examined the
dew: but I could find nought in it worthy of remark.
However, seeing that my shoes also had got reddened by
the grass, I turned my attention to the grass itself, and
saw that some of it was studded with reddish dots.
Bringing these before my microscope, 1 saw that they
consisted of small globules, whereof upwards of a thousand
did not equal the bigness of a small sand-grain. (I find
there are various kinds of grass: and among others, one
sort that was very rough, which was not contaminated °*.)
Inquiring after a reason for these globules being upon the
’ Probably a reference to malaria, and therefore of some interest at the
present time.
> Marginal note in original.
LETTER 26. 27 SEPTEMBER 1678 181
grass, I observed that they came not out of the air (as
was the vulgar opinion), but out of the grass itself: the
cause whereof I conceived to be this. The dry cold, that
we had some three weeks earlier, caused the death of the
extreme tips of some blades of grass; and this was followed
by very warm weather, which drove fresh nourishment
again upwards through the pores’ in the grass. But this
food-matter, wherewith the pores of the grass were filled,
being unable to get out at the top (because the ends or
the uppermost pores of the grass were stiff and dried up),
burst open the pores in many places where they were
most weakened ; and thus many globules were squeezed
out of them. These globules, lying stuck together upon
the outside of the grass, and becoming stiffer on exposure
to the surrounding air, took upon themselves a reddish
colour; whereas these same globules, when they le in-
closed in the pores, are green.” And whenever one
happens to strike one’s foot against such grass, the said
globules are dusted off it, and make one’s shoes reddish.
But since a red colour is most agreeable with the notion
of fire, we must not take it amiss in the common man if
he deems the said substance to be a fiery matter: seeing
that there are among us physicians (who fancy themselves
experienced) who say, when they see blood whose whey-
like matter * is yellow, that the blood is bilious; or say of
black blood, that ’tis burnt: just as if everything yellow
were bile; and everything black, burnt.’
Meantime the Fellows of the Royal Society’ had not been
wholly idle in the matter of the “little animals.” Robert
* Port MS.
> L. evidently confused the red corpuscles on the grass-blades with
chloroplasts within them.
* i.e, serum.
* It is clear from this, and many another passage in L.’s writings, that
he had but a poor opinion of the general medical practitioner of his day.
*> The Fellows (or some of them) would perhaps have taken particular
interest in the observations on infusions: for they would recall—unlike
“ec
182 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
Hooke, who succeeded Oldenburg in 1677 as Secretary,
himself repeated the experiments with pepper-water and other
infusions. In 1678 he published’ some account of his obser-
vations, which confirmed Leeuwenhoek’s findings: and his
experiments were also briefly communicated to Leeuwenhoek
by letter at the end of 1677. Hooke’s published description
records that he succeeded in seeing the animalcules—-or some
like them—described by Leeuwenhoek: “some of these,” he
says, “so exceeding small, that millions of millions might be
contained in one drop of water.”* A draft of Hooke’s unpub-
lished letter is still in possession of the Royal Society; and as
it contains several points of interest J will now give it. He
wrote °:
The papers you directed to the Lord Brouncker* were
read at a full meeting of the Royall Society and very
kindly accepted by the Members thereof and they have
orderd me to returne you both their thanks for soe freely
communicating your observations, and also an account
of what hath been here done in order to verify your
observation concerning the small animalls you have first
discovered in Pepper-water.
Having steeped then in Raine water pepper wheat
most modern Fellows—that Bacon, whose writings had so profound an
influence upon the Society at its inception, had emphasized the need of
inquiry into the various substances which produce animalcules by putre-
faction. Cf. Nov. Org., Lib. II, cap.50: “Etiam materiae diversae putre-
factionum, unde animalcula generantur, notandae sunt.”
* See Lectures and Collections made by Robert Hooke (1678). Part II,
Microscopium. Also reprinted in Lectiones Cutlerianae (1679).
* Ibid., p.83. Hooke evidently refers to bacteria—not protozoa.
* MS. letter (unpublished)—R. Hooke to Leeuwenhoek, Dec. 1 [?— date
partly obliterated], 1677. Roy.Soc.MSS. The original is in English, and
I give it exactly as written—only omitting a part at the end which has no
bearing upon the subject under consideration. I have merely expanded
words which are contracted in the original—for the reader's convenience,
and for typographical reasons. The letter is in Hooke’s own hand, and is
signed “ your very great admirer and honorer R.H.”
* William, second Viscount Brouncker (1620 ?—1684)—an Irish peer.
He was M.D. (Oxford) and a mathematician, and an original Fellow and
first President of the Royal Society on its re-foundation in 1662-3.
HOOKE’S CONFIRMATIONS 183
barly oats pease and several other graines,' and having
fitted up some microscopes which had layne a long
while neglected, I having been by other urgent occupa-
tions diverted from making further inquirys with that
Instrument, I began to examine all those severall Liquors
and though I could discover divers very small creatures
swimming up and down in every one of those steepings
and even in Raine it self and that they had various
shapes & differing motions, yet I found none soe ex-
ceedingly filled and stuffed as it were with them as was
the water in which some cornes of pepper had been
steeped. Of this the President & all the members
present were satisfyed & it seems very wonderfull that
there should be such an infinite number of animalls in
soe imperceptible a quantity of matter. That these
animalls should be soe perfectly shaped & indeed with
such curious organs of motion as to be able to move
nimbly, to turne, stay, accelerate & retard their progresse
at pleasure. and it was not less surprising to find that
these were gygantick monsters in comparison of a lesser
sort which almost filled the water.
It seems clear that the ‘“gygantick monsters’’ were
protozoa, while those of the “lesser sort” were bacteria. The
foregoing lines contain, I believe, the first mention of the
discovery of any of these organisms in infusions of wheat,
barley, oats, and peas: for none of these are recorded by
Leeuwenhoek as having been used in making the “ steepings 4
employed in his own experiments. It is therefore unfortunate
that Hooke—so far as I can ascertain—never wrote any
further descriptions of the organisms which he discovered.
Rumours of these remarkable discoveries spread, it would
appear, into even the highest circles : for in another letter from
Hooke to Leeuwenhoek, written a little later, the following
passage occurs *:
1 At a slightly later date—at a meeting of the Society on 7 March
1678—Hooke also demonstrated the presence of “ animalcules ” in infusions
of aniseeds and coffee. See Birch, Vol. TEE paso.
2 MS. letter (unpublished), R. Hooke to Leeuwenhoek, dated 18 April
184 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”’
The prospect of those small animalls have given great
satisfaction to all Persons that have viewed them. His
majesty * having been acquainted with it, was desirous to
see them and very well pleasd with the Observation and
mentiond your Name at the same time. I know not
whether any of the ways I have here made use of for the
Discovery of them may be in any thing like those with
which you make your observations. But I have two or 3
other ways which I shall shortly communicate,’ that doe
farr exceed those I have here mentiond.’
Some important additional particulars regarding Hooke’s
observations can be gathered from Birch’s History. He tells
us* that at the meeting of the Society held on 1 November
1677 O58),
There were produced a great many exceedingly small and
thin pipes of glass of various sizes, some ten times as big
as the hair of aman’s head; others ten times less. These
were made, in order to try a conjecture of Mr. Hooke
propounded to the Society, that the discoveries, affirmed
to be made by Mr. Leewenhoeck, were made by help of
1678 (Roy. Soc. MSS.). The original, of which only a part is here copied,
is in English. It is written in Hooke’s hand and signed “R.H.”’ I again
expand the abbreviations in the original, for the reader's convenience.
1 j.e., King Charles II of England, “ Founder” and Patron (Fundator et
Patronus) of the Royal Society—as he is styled in the Charta secunda of
1663.
2 The communication will be found in Hooke’s Lect. & Collect. (1678),
p. 89 et seqq.
* This letter from Hooke is referred to by L. at the end of his own
Letter 28, 25 April 1679, to N. Grew (Brieven I, p.13: first published in
Dutch in 1686). As the 28th Letter deals largely with spermatozoa, it has
often been erroneously inferred that Hooke demonstrated spermatozoa—not
protozoa—to the King. But the correspondence between Hooke and L.
affords no grounds for such an inference; and I have been unable to
discover any evidence in support of the accepted belief that the Merry
Monarch was once entertained at an exhibition of spermatozoa by the
Royal Society (or any member thereof). This myth probably originated
with Haller (Elementa [1765], VII, 523)—as Cole (1930, p. 14) has already
noted.
* Birch, Vol. III, p. 346.
WITNESS OF ROYALTY AND THE ROYAL SOCIETY 185
viewing with a good microscope such small pipes contain-
ing the liquor or water, in which those multitudes of
exceedingly small insects or animals wriggling among
each other are discovered; for that he alledged, that the
said pipes being filled with liquors became themselves as
it were magnifying glasses. . . . . . It was therefore
ordered, that against the next meeting pepper-water should
be provided, and some better microscope than that made
use of, that the truth of Mr. Leewenhoeck’s assertions
might, if possible, be experimentally examined.
Accordingly, at the next meeting, on 8 November 1677,
“the first thing exhibited was the experiment charged on
Mr. Hooke at the last meeting, of examining pepper-water with
better microscopes and thinner and small pipes.”* But the
experiment was not wholly satisfactory, and various objections
to the observations were raised by the Fellows present. At
the following meeting, however, on November 15, ample
confirmation was forthcoming. In the words of Birch :*
The first experiment there exhibited was the pepper-
water, which had been made with rain-water and a small
quantity of common black pepper put whole into it about
nine or ten days before. In this Mr. Hooke had all the
week discovered great numbers of exceedingly small
animals swimming to and fro. They appeared of the
bigness of a mite through a glass, that magnified about
an hundred thousand. times in bulk; and consequently it
was judged, that they were near an hundred thousand
times less than a mite. Their shape was to appearance
like a very small clear bubble of an oval or egg form;
and the biggest end of this egg-lke bubble moved fore-
most. They were observed to have all manner of motions
to and fro in the water; and by all, who saw them, they
were verily believed to be animals; and that there could
be no fallacy in the appearance. ‘They were seen by Mr.
' Birch, Vol. III, p. 349.
* Bireh, Vol: IL, p: 352.
186 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”
Henshaw, Sir Christopher Wren,’ Sir John Hoskyns,°
Sir Jonas Moore,‘ Dr. Mapletoft,? Mr. Hill,® Dr. Croune,"
Dr. Grew,* Mr. Aubrey,’ and divers others; so that there
was no longer any doubt of Mr. Leewenhoeck’s discovery.
Leeuwenhoek’s next communication on the “ animalcules’’
in infusions was sent to Robert Hooke, and is very brief; but
it was accompanied by a copy of a very curious and interesting
letter which he had previously written to Constantijn
Huygens. In the letter to Hooke he says:
As I see and hear that you are a man much given to
speculation, I have thought fit to send you a copy of a
very rough calculation which I set down on paper at
the urgent intreaty of Mr. Constantijn Huygens van
1 Thomas Henshaw (1618-1700), barrister and author: Vice-President
and an original Fellow of the Society. Cf. Dict. Nat. Biogr.
* Christopher Wren (1632-1723), artist and famous architect—soon to be
President of the Society (1680)—too famous to need further annotation.
* John Hoskyns (1634-1705), barrister of the Middle Temple: later
Secretary and President of the Society. Cf. Dict. Nat. Biogr.
* Jonas Moore (1617-1679), mathematician and surveyor. Elected F.RB.S.
in 1674. He is several times mentioned by Pepys in his Diary, and his life
is given in the Dict. Nat. Biogr.
* John Mapletoft (1631-1721), M.D. and D.D., of Trinity College,
Cambridge. Elected F.R.S. in 1676. He was an intimate friend of John
Locke, and before he became a divine practised medicine in London with
Sydenham.
* Abraham Hill (1635-1721), Treasurer of the Society, and an original
Fellow. Commissioner of Trade in 1689—a business-man of no known
scientific attainments.
” See p. 48, note 2, supra.
* See p. 168, note 4, supra.
* John Aubrey [sew Awbrey] (1626-1697), the well-known antiquary ; an
original Fellow of the Society.
* From Letter 29a. 16 January 1680. MS.Roy.Soc. An English extract
from this letter—and its enclosure—was published in Derham’s Philos.
Expts. & Obss. of R. Hooke (1726), p. 55. (The letter is there incorrectly
dated Jan. 6.) I translate from the Dutch original—A contemporary
English MS. translation is preserved with the original Dutch MS. in the
Roy. Soc. collection, but it has given me no help. The letter was read at
the meeting of the Society on 22 Jan. 1680 [0.S.], and discussed at the
following meeting on Jan. 29. See Birch, Vol. IV, p. 5.
LETTERS TO HOOKE AND CONST. HUYGENS 187
Zuylichem.* And I feel bound to say, furthermore, that
last Friday evening I took some pepper-water, in which
there were many living animalcules, and mixed it with
about a like amount of rain-water, wherein I had put a
quantity of pounded ginger: and forthwith examining
this mixt water, I found that the animalcules were slow
a-moving. Some hours afterwards, examining this water
anew, I could perceive no animalcules whatsoever in it :
but about twice 24 hours afterwards, I saw very distinctly
some animalcules which I judged to be a hundred million
times smaller than a sand-grain, but without being able
to discern any of those animalcules that had been before
in the pepper-water.”
The enclosed letter to Constantijn Huygens, dated 20 May
1679, I shall now give in full. The original, from which it
was copied, is preserved among the Huygens manuscripts at
Leyden *—the following being a complete translation of the
copy sent to Hooke:
Along with this goeth my calculation, which I confess
is quite imperfect, seeing that my estimates were made
by the eye alone.
I have oft-times let my thoughts run on the extreme
small vessels and sinews* wherewith the very little
* The father of Christiaan Huygens the astronomer and mathematician—
not his elder brother. Cf. p. 42, note 2, supra.
* It is probable that the animalcules in the pepper-water were protozoa
of some sort, which were killed when the ginger-water was poured upon
them: while the very minute forms which developed in the mixture after
48 hours were evidently a new crop of bacteria.
* See Haaxman (1875), p. 136,—where the date is given as 21 May
1679: but L.’s copy, sent to Hooke, is by himself dated May 20, as stated
above. The copy was made with his own hand.—The original has recently
been printed in full in Guvr. Compl. de Chr. Huygens, VIII, 168-172 (also
there dated May 21).
* Or “nerves”: MS. senwwen. Zenww nowadays means a nerve—as it
often did to L.—but at an early date it also meant a sinew (tendon), and
from what follows this seems to be the correct rendering here. (Cf. the
original meaning of Lat. nervus and Gr. vedpov.)
188
ce
LEEUWENHOEK AND HIS LITTLE ANIMALS ”’
animalcules are furnished withal; and more especially
when I have been asked, whether I am able to see the
particles of water itself? T’o which I did often answer,
that there be little animals in water that are many
million times smaller than a sand-grain; and that these
little animals, on which I can discern no feet, must not-
withstanding be furnished with instruments for motion ;
and that these instruments must themselves consist, in
part, of blood-vessels which convey nourishment into
them, and of sinews which move them; and that through
these vessels, moreover, water must also pass. And this
being so, we must suppose the particles of the water itself
to be so small as to be, for us, inconceivable: and I’m
persuaded that no man will ever advance so far in science
as to be able to gaze upon the particles whereof water
itself consisteth.
I shall here first lay down the proportion which the ©
animalcules bear to a sand-grain, in so far as my eye is
able to arrive at it; together with the number of
animalcules proportionate to the bigness of a cubic
inch.
I usually judge that three or four hundred of the
smallest animalcules, laid out one against another,
would reach to the length of the axis of a common grain
of sand; and taking only the least number (to wit 300),
then
27000000 animalcules together are
as big as a sand-grain.
Let’s assume that such a sand-grain is so big, that
80 of them, lying one against the other, would make up
the length of one inch as BC [Text-fig. 1].
LETTER TO CONST. HUYGENS. 20 may 1679 189
80 sand-grains in the length of one
80 inch.
6400 sand-grains in a square inch.
80
p 512000 sand-grains in a cubic inch.
27000000 animalcules which make
3 up the bigness of a
(Text-Fic. 1.] sand-grain.
amounting to 1382400000000 animalcules in a cube
inch, as ABCDEF.
This number of animalcules is so great, that if one had
as many sand-grains, of the bigness aforesaid, then one
could lade with them more than 108 of our ordinary sand-
lighters; that is, reckoning one schagt of sand (which is
144 cubic feet) to every lighter.
I have let my thoughts run likewise on the very
little vessels that are in our bodies, and have judged that
they are above a thousand times thinner than a hair of
one’s head; and I have therefore put the proportion of
the very little vessels thus in relation to the body, in
order to arrive afterwards at the proportion of the
vessels in the little animals.
First of all, I sought to know how many hairbreadths
are equal to the length of one inch; and having by me a
copper rule, whereon the inches are divided into 3 parts,
and each of these again into 10 parts (thus altogether, an
inch divided into 30 parts), I laid hairs from my periwig
upon these divisions; and observing them thus through
a microscope, I judged that 20 hairbreadths are equal to
3a of an inch. Consequently, there are 600 hairbreadths
in the length of one inch.
Further, I measured, roughly, the thickness of my
body above the hips, and judged (taking one thing with
another) that the diameter of my body was 8 inches.’
‘ If this were approximately correct, then L. was considerably more
190 LEEUWENHOEK AND HIs ‘“‘ LITTLE ANIMALS ”’
Archimedes showeth that as 14 is to 11, so is the square
of the diameter to the content of a circle.’
14—11—8
8 704
64 14 507 square inches for my body’s thick-
11 ness.
704
600 _hairbreadths in a length of one inch.
33 diameters of the very little vessels in
our bodies for one hairbreadth (that
is, reckoning the little vessels in our
bodies 1089 times thinner than a
hair)
gives 19800 little vessels in a length of one inch.
19800
gives 392040000 little vessels to a square inch.
50 square inches for the body’s thickness
gives 19602000000 vessels in the thickness of the body.
If we now suppose that the little vessels bear the same
proportion to the bodies of the little animals, as those in
us do to our bodies; then, in order to compare the very
little vessels of the animalcules with the thickness of a
sand-grain, the number given above must still be multi-
plied by 300 (since, as already said, a sand-grain is 300
times thicker than an animalcule).
——$————
slender than the apparently heavily-built man depicted in his portraits.
Moreover, the statement is not easy to reconcile with the later record that
at this date he weighed over 11 stone (ef. p. 222 infra).
* Nowadays we usually find the area of a circle by 77°; but “/y X d’ is
obviously the same thing, and Prof. D’Arcy Thompson informs me that it is
actually in this form that the proposition is found in the Circuli Dimensio of
Archimedes.—It is highly improbable, of course, that L. had ever studied
the writings of this great mathematician.
SOME ‘‘ CURIOUS MATHEMATICKS ”’ 191
Consequently, if the thickness of 19602000000
ar pe 300
a sand-grain is 1, the vessels in cae A eee
the little animalcules are 5880600000000
And because this number is so exceeding great, I have
thought good to express the proportion in terms of a
hair’s breadth in relation to the circumference of the
earth.
5400 miles’ for the length of the circumference
2000 rods for every mile
gives 10800000 rods for the circumference
12 feet for one rod
g1ves 129600000 feet for the circumference
12 inches in one foot
gives 1555200000 inches in the circumference
600 hairbreadths in one inch
gives 933120000000 hairbreadths for the length of the
circumference.
This number of hairbreadths, which is equal to the
length of the circumference of the earth, even when again
multiplied by 6 will not equal that number aforesaid
which represents the proportion of the vessels in the little
animals to the thickness of a sand-grain (as we have
estimated it above). To sum up, then:
As a sixth of a hair-breadth is:
To a length of 5400 miles:
So is one of the smallest vessels in the smallest
animalcules :
To the thickness of a sand-grain (of such size that
80 thereof, lying one against another, equal a
length of one inch).
Sir, you have here the wonderful proportions that I
‘ Leeuwenhoek’s ‘‘ mile’’, consisting of 2000 “rods” of 12 feet, is, as a
simple calculation shows, equal to some 4% English miles. (The English
mile = 320 rods, and the English rod = 162 feet.)
cc
192 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”’
conceive to exist in the secret parts of Nature: and from
this appeareth also, that all we have yet discovered is but
a trifle, in comparison of what still lies hid in the great
treasury of Nature; and how small must be those particles
of water’ which, to all appearance, pass many at a time
through such tiny vessels.
I hope that with this I have satisfied your require-
ments.”
I have given the foregoing letter in full for several reasons.
In the first place, it serves to illustrate Leeuwenhoek’s fond-
ness for simple mathematical deductions ; secondly, it shows
very clearly that, in the case of his “smallest animalcules”’, he
was dealing with bacteria; and thirdly, it shows the success
and failure of the application of his “uniformitarian” principles
to microscopic creatures. In his estimate of the size and
numbers of the bacteria present in a minute drop of water, he
was not mistaken: but when he proceeded to show, by simple
arithmetic, the magnitude of the blood-vessels in such
organisms, he went ludicrously astray. His education and
his century both failed him. His greatness and his littleness
are here revealed simultaneously—to those endowed with the
accumulated knowledge of the next 250 years. Yet even at
the present day Leeuwenhoek’s mistaken conclusion may
serve as a warning to the biologist with statistical tendencies.
It is surely worthy of remembrance, even now, that the most
flawless mathematical calculations may sometimes be wholly
erroneous.
Leeuwenhoek’s next observations on ‘‘animalcules” are
contained in a further letter to Robert Hooke. After
recording some observations of no* present interest, the letter
ends thus: *
a
" j.e., the molecules of which water itself is composed.
> Referring to Const. Huygens’s request that he should put down on
paper his calculations concerning the magnitude of the parts of the “little
animals”’ (vide supra).
° A few words which are perhaps not irrelevant to the present subject
will be referred to later (see p. 207 infra).
* Letter 30. 5 April 1680. To R. Hooke. MS.Roy.Soc. Published in
Brieven, Vol. I (Dutch), and Opera Omnia, Vol.I (Latin): also an English
abstract in Phil. Trans. (1693), Vol. XVII, No. 196, p. 593; but this does
not include the passage here quoted.
LETTER 30. 5 APRIL 1680 193
In the court-yard of my house there stand two vines;
and observing their growth to be such, that a moisture
dripped from their shoots, I examined this sap on several
successive occasions, just to see if I could discover any
living creatures in it: and most times I discerned therein
divers kinds of living animalcules, whereof one sort was
uncommon big in comparison of the others; nay, I even
saw some little animals that I had seen aforetime in
divers sorts of water. Hereupon I repaired to my
garden which lieth within this town, and there too I
examined the sap dripping from the vines, but in it I could
discover no living creatures, save only a little worm that
was of an uncommon bigness,’ compared with the other
animalcules. I betook myself thence to my garden which
lieth without the town, and there again examined the sap
from several vines, but could discover no living animalcules
in it. I cut off pieces from two vine-branches, to make
them drip the more, and went to examine the sap again
next day, but could find therein nothing living. And
I took a new glass phial, and caught the sap in it, and
carried it home and examined it; but notwithstanding,
I could perceive no living animalcules in it. I am
now busy finding out, if ’tis possible, why there be living
animalcules in one sap, but none in the other.
A little later Leeuwenhoek addressed another letter on
the same subject to Dr Gale,” and in it recorded the results
of his further experiments and observations on the sap of vines.
This letter is as follows: °
* Probably a nematode.
* Thomas Gale (1635 ?—1702), a Doctor of Divinity, was at this time
Secretary of the Royal Society—an office to which he was appointed in
November, 1679. He was a Fellow of Trinity College, Cambridge, and
Professor of Greek in the University from 1662 to 1672. Later (1697) he
became Dean of York.—At the beginning of this letter L. says that he is
writing to Gale because Hooke had informed him that Gale was become
Foreign Secretary, and that he should therefore address his letters to him
in future.
° Letter 81. 13 May 1680. To Thomas Gale. MS.Roy.Soc. Printed
1Ue5;
194 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS ”’
This serves as a continuation of my letter of the 5th of
April [1680], wherein I noted how I had observed living
animalcules* in the sap leaking from the shoots of the
vine standing in my court-yard; whereas in the sap
which dripped from the vines in my garden, I could
discover no living creature. I have divers times turned
my thoughts to this matter, and can find no more
satisfactory explanation thereof than the following :
The rain-water, which is drawn aloft by the power of
the sun, and forms the clouds, is commingled with the
seed of these animalcules; and as it had been raining for
several days running, before the date of my first observa-
tions on vine-sap, the tags of leather, wherewith the
branches of the vine were nailed fast against a stone
wall, had become quite water-logged; but afterwards there
followed a warm sunshine, which caused the vine-branches
to drip, and thus the foresaid leathern tags were kept
continually wet, by the dripping of the vine upon them;
and in this manner not only did divers sorts of animals
come forth from this rain-water, but they even (so I
imagine) bred in it, and swam along the vine-branches,
even to the topmost part of the vine, where the moisture
dropped out.
About 24 hours after I had dispatched my observations
to Mr. Hooke, the vine-branches in my court-yard
stopped dripping, and the weather grew uncommon warm,
so that the vine-branches, and the leathers as well, got
quite dry: hereafter, it rained near the whole night, then
the sun shone in the morning, and it rained afresh in the
afternoon: and observing that the leathern tags (with
which, as remarked above, the branches of the vine were
nailed fast to the wall) were once more soaked through, I
in Brieven, Vol. I (Dutch), Opera Omnia, Vol. I (Latin), and briefly abstracted
in English in Phil. Trans. (1693), Vol. XVII, No. 196, pp. 593-4,—along
with the preceding letter. It was presented at a meeting of the Society on
« 13 May 1680 [0.S.] (Birch, Vol. IV, p. 37). I translate the whole letter,
with the exception of a few words at the beginning and the end.
1 The MS. says Dierkens, but the printed letter has Dieren (=animals).
LETTER 31. 138 may 1680 195
examined the water that lay upon them, and in it I
discovered! sundry little animals of the biggest sort
previously seen in the sap aforesaid, and I saw some of
a lesser sort lying dead: and when I examined these
animalcules more narrowly, I found that they belonged to
two kinds commonly present in ordinary waters.’ After
this time, about the middle of April, it rained a whole day,
and the night following ; and next morning, when the
sun came out, I betook myself to my garden, and
[examined]* the sap dripping froma vine-branch, which
I had cut a few days before, in order to make it drip, at
the same time tying or binding a strip of wash-leather
around it, so that when it rained, the rain-water would
stay caught in it, and not readily dry up, and thus get
better mixed with the sap that dripped out: and in this
water I discovered a few animalcules of the sort already
described. I also examined the sap from a second vine,
which I had likewise treated in the same way, and herein
too I perceived the animalcules. I also visited a third
vine, from which I had also previously cut off a branch,
so that it would drip;* but this one I did not tie round
with a leather, and I took the sap that ran down the
branch at the place where it was most plentiful (namely,
in a fork, where the shoot came off the stem); but I
Aw «mA
(Text-Fic. 2.]
could perceive no living animalcules in it, though I saw in
it, with admiration, many little chrysalises, or pupae, as
in Fig. A A [see Text-fig. 2]: and although they were
' gesien MS. ontdekt printed version.
2 It is obviously impossible to identify these “animalcules”, though
they were probably protozoa or bacteria of some sort.
> A verb is here accidentally omitted from the MS. and also from the
Dutch printed version. The sense evidently requires “examined” or
“ observed’: and as the Latin translator supplied “ examinavi # do
likewise. .
4 These words (op dat die druipen soude) are in the printed version but not
in the MS.
196 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
more than a million times smaller than a coarse sand-
grain, yet could I see very plainly that they were furnished
with 5 joints. This appeared very strange to me, as I
had formerly convinced myself that no water-animalcules
proceed from such structures, and I had never conceived
that animalcules of such littleness could live in the air.
I took these chrysalises home, and put some of them in the
air, to see what would come out of them; but within a
few days, they got so dry that their former figure was
scarce discernible ; and those which I meant to keep in
water got lost.
These trifles are all I have to tell you for the time
being.’
The foregoing characteristic observations upon protozoa
(or bacteria) show us an interesting picture of Leeuwenhoek
at work—discovering new ‘‘animalcules” in new situations,
wondering how they make their appearance and multiply in
certain liquids, and endeavouring to account for their appar-
ently erratic distribution. Soon afterwards he again attacked
the problem of their generation, and sent the following account
of his experiments : *
When it became known to me that divers opinions
have been expressed concerning the generation of little
animals; and as I heard, especially, that a certain
Gentleman’ hath writ that no living creature can be
generated if the vessel, or bottle, in which any moisture
or meat has been put, be tightly stoppered ; I had a mind
to carry out some trials of this matter.
* This sentence is in the MS. but not in the printed version.
* From Letter 32. 14 June 1680. To Thomas Gale. MS.Roy.Soc.
Printed in Brieven, Vol. I (Dutch) and Opera Omnia, Vol. II (Latin). No
abstract of this letter was published in the Phil. Trans. though the letter is
a very remarkable one. It contains, in addition to the observations here
related, a description of yeasts obtained from beer—the first microscopic
study of these organisms.
* Doubtless Francesco Redi, whose celebrated treatise on “‘ the Genera-
tion of Insects”’ first appeared in 1668. LL. could know of Redi’s work only
by hearsay, since he was ignorant of Italian.
eva Lan)
ie ne; mint i
aes mies:
hin a Nhat:
il “ul ih ‘ae
uy Ms wt
me LAr Ay
a rat aoe
bes re hah Naa haa
I Se
wn Ce ~ Nhneaia Mea wor aN nel ;
ee Y aw Te), ;
Aah, ‘eo iat ait) Nae ee se a
Wh en hay yi Ha) od a py
hi Se ey yi ia, ay es Wi, wine ia, ne
oe mete, Slots oh
we Ae , :
PLATE XXII
Ss
pr
yp
ANNAN ass A
A FIGURE FROM LETTER 32 (14 JUNE 1680)
illustrating the experiment with the pepper-
tube. On the left, Leeuwenhoek’s original
drawing (reduced to #): on the right, the same
figure as improved by the engraver for re-
production in the printed letter (same size).
facing p. 197
LETTER 82. 14 JuNE 1680 197
Accordingly, I took two glass tubes, as ABCDEFHIKL
[Plate XXIT], which, after they were both closed below at
AL, were filled up to BK with pounded pepper, and then
to CI with clean rain-water, as soon as it had been
collected on May 26* in a clean china dish (in which no
victuals had been put for quite ten years); then, by the
heat of the flame, the glass was fashioned to the figure of
ABCDGHIKL, having at its pointed end G a small
opening ; for I considered that though the glass was now
hot, the air within it would presently become equally cold
with the air that was outside it; and after the lapse of
about a quarter of an hour, I sealed up the aperture at G
tight, by means of the flame. I also prepared myself a
second glass, treating it likewise, save that in this I left
the aperture at G open; in order to ascertain, if ’twere
possible, in which water the living animalcules would first
turn up. But after it had stood thus for three days,
during which time I made divers observations upon it, I
judged that if there were already any very little living
animalcules in this water, ’twould not be possible for me
to discover them, for the reason that the glass was too
thick, and because of the many little particles of pepper
which lay against the glass inside, so that it was not
feasible to carry out such particular observations as the
occasion required. On this account, I took a little water
out of the second glass, through the small opening at G;
and I discovered in it a great many very little animalcules,
of divers sorts and moving about among one another,
each several sort having its own particular motion. But
as the first tube was of a somewhat thinner glass, I left it
shut up till the fifth day, and during that time made
various observations upon it; but I could discover no
living animalcules in it, so I resolved to break the glass
open at G, and in breaking it, the air which had thus
been shut up for 5 days within it (and which was much
" Anno 1680.
198 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
compressed by the air-bubbles which rose everywhere to
the top of the water) escaped with force out of the tube:
for which reason I rather fancied that there would be no
living creatures in this water. But I found the contrary:
for no sooner did I draw some water through the small
opening I had made at G, and bring it before my micro-
scope, than I perceived in it a kind of living animalcules
that were round, and bigger than the biggest sort that I
have said were in the other water, though they were yet
so small that it was not possible for me to discern them
through the thickness of the glass tube.’ After this tube
had stood thus open for 24 hours, I examined the water
again ; and I then saw, besides the foresaid animalcules,
various other sorts, though they were so small that they
were hard to make out.
Still, I bethought me that when that Gentleman afore-
said spake of living creatures”, he meant only worms or
maggots, which you commonly see in rotten meat, and
which ordinarily proceed from the eggs of flies, and which
are so big that we have no need of a good* microscope to
descry * them.
The whole of the foregoing passage (as printed in Dutch)
has recently been copied and learnedly commented upon by
Prof. Beijerinck (1913), who himself repeated the experiments.
He infers that the “animalcules”? which Leeuwenhoek dis-
covered were undoubtedly bacteria—not protozoa—and that
among them were probably (as he found in his own experiments)
Bacillus coli, Azotobacter, and Amylobacter saccharobutyricum.
It was to this last species, he thinks, that the “ bigger sort ”’
which were found in the sealed tube probably belonged.
Beijerinck also points out that these are the earliest known
observations on any anaerobic bacteria: but although
' So in the printed version. The MS. has “ for reasons already men-
tioned ”’ (voor de verhaelde oorsaeken).
> dierkens MS. schepsels printed version.
* goet is in printed version, but not in MS.
* bekennen MS. beschowwen printed version.
ANAEROBIC BACTERIA DISCOVERED 199
Leeuwenhoek discovered that organisms could live and
multiply under the hemi-anaerobic conditions present in his
closed tube, he was unable at that time, of course, to realize
the full importance of his discovery. I have also confirmed
the foregoing observations, though I made no attempt to
determine exactly what species of bacteria were present in
the tubes—being satisfied with Prof. Beijerinck’s authoritative
opinion. Iam also satisfied that no protozoa can usually be
obtained in experiments such as the above if the procedure
described be adhered to.
It seems remarkable that Leeuwenhoek—always a vigorous
opponent of the doctrine of spontaneous generation—appears
to have made no further study of the very interesting pheno-
mena which the foregoing experiments record. He must
have been puzzled, at first, to account for the appearance of
bacteria in his sealed tube: but I think his own words supply
the explanation which occurred to him, and which apparently
satisfied him at that time. In previous letters’ he makes the
suggestion that ‘“‘ animalcules” or their “ seeds ”’ are present,
or can exist, in rain—being drawn up into the clouds with
the water in which they live or are formed, and subsequently
scattered when the rain falls. Consequently, he probably
imagined that the rain-water introduced into the sealed tube
already contained ‘“ animalcules” —or “seeds”? capable of
germinating into “animalcules”»—-which found sufficient
‘air’ in the tube to enable them to live and breathe and
multiply for at least some days. Nearly a hundred years
subsequently elapsed before any further light was shed on this
subject by the ingenious experiments of Spallanzani, though
it was not until much later that the problem was solved—
more or less completely—by Pasteur and Tyndall. Redi’s
famous observations by no means solved the problem of
spontaneous generation—as is often lightly stated: and this
point is clearly brought out by Leeuwenhoek’s experiment, as
he himself apparently realized; though he made no attempt—
or, at least, recorded none—to push his inquiries any further.
A few months after he had written the foregoing letter to
Dr Gale, Leeuwenhoek wrote again to Dr Hooke: and in
" Cf. Letter 18 (p. 163) and Letter 31 (p. 194).
a3
200 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
the course of his letter he gave some further details concerning
the animalcules in pepper-water. His words are as follows: *
Some days ago I once more poured water upon some
pounded pepper; and a few days later, I saw, among
others, two kinds of animalcules’ in it; and moreover,
there seemed to be big and little ones of either sort,’ so
that methought the big ones were full-grown, and the
little ones their young; and at the same time I imagined
that in the biggest sort of these animalcules I could see
the young, or maybe their eggs, inside their bodies. And
I imagined, besides, whenever I saw two little animals
entangled together, either swimming or lying still, that
they were a-copulating.
* Whereas I suffer many contradictions, and oft-times
hear it said that I do but tell fairy-tales about the little
animals, and that there are people in France who do not
scruple to say that those are not living creatures which I
exhibit, and that if such water be boiled, the particles
which one imagines to be animals still continue to move ;
yet notwithstanding, I have demonstrated the contrary
" From Letter 33. 12 November 1680. To R. Hooke. MS.Roy.Soc.
Printed in Brieven, Vol. I (Dutch), and Opera Omnia, Vol. II (Latin). An
incomplete English translation was published in Phil. Collect. of R. Hooke
(1681), No. 3, pp. 51-58. The whole letter was first published in Dutch in
1684 (Ondervindingen en Beschouwingen, etc. pp. 1-32): while the full Latin
version appeared in 1695 (Arc. Nat. Det.)—It should be noted that in the
earlier part of this letter—not here translated—L. casually mentions that
he “ saw some little animalecules swimming” (p. 8, Dutch printed version)
among various © globules’? which he found in rain-water that he had put in
a special piece of apparatus. They were probably protozoa or bacteria; but
as no further mention is made of them, they are not identifiable.
* Evidently ciliates.
° dat yder soorte groter en kleynder haar vertoonde printed version (1684)
dat ijder in sijn soort bestonden uijt groote en kleijne dierkens MS. (1680).
‘ Probably a misinterpretation of the inclusions in food-vacuoles.
° The lines following, as far as the calculations on p. 203, have been
translated by Hoole (1798) in his Introduction, pp.iv-vi. His rendering is
faithful in substance, though not always in diction. In translating L. he
allowed himself more latitude than I have done.
LETTER 33. 12 NOVEMBER 1680 201
to divers distinguished Gentlemen, and I make bold to say,
that people who say such things have not yet advanced so
far as to be able to carry out good observations.
For my own part, I can say with truth, that the smallest
sort of which I shall here speak, I see alive and exhibit as
plainly to my eye as one sees, with the naked eye, little
flies or gnats sporting in the air, though they may be
more than a hundred million times less than a coarse
grain of sand ; for not only do I observe their progression,
both when they hurry, and when they slow down, but
I see them turn about, and stand still, and in the end
even die; and those that are of a bigger sort,’ I can also
see running along as plain as you see mice before
your naked eye; nay, in some I can even see the inward
parts of their mouth, as they stick them in and out, and
make play with them; indeed, in one sort I see the very
hairs on their mouth, though they themselves are several
thousand times less than a sand-grain.
As they’ll say ’tis not credible that so great a many of
these little animalcules can be comprehended in the
compass of a sand-grain, as I have said, and that I can
make no calculation of this matter,” I have figured out
their proportions thus, in order to exhibit them yet more
clearly to the eye: Let me suppose, for example, that
I see a sand-grain but as big as the spherical body ABGC
[Text-fig. 3, p. 202] and that I see, besides, a little animal
as big as D, swimming, or running on the sand-grain; and
measuring it by my eye, I judge the axis of ° the little
animal D to be the twelfth part of the axis of the
supposed sand-grain, AG ; consequently, according to the
" From the descriptive details which follow, L. evidently refers here to
ciliates.
* The beginning of this sentence—up to the point here marked—is worded
differently in the MS. and in the printed version. The meaning is, however,
identical in the two.
* van (of) is here omitted from the printed version—by a misprint—but
is present in the MS.
202 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS”
ordinary rules, the volume of the sphere ABGC is 1728
times greater than the volume of D. Now suppose I see,
among the rest, a second sort of little animals, which
i
(Text-Fie. 3.]
I likewise measure by my eye (through a good glass, giving
a sharp image); and I judge its axis to be the fifth part,
though I shall here allow it to be but the fourth part (as
Fig. E), of the axis of the first animalcule D; and so,
MICROMETRIC METHODS 203
consequently, the volume of Fig. D is 64 times greater
than the volume of Fig. E. This last number, multiplied
by the first number [1728], comes then to 110592, the
number of the little animals like Fig. E which are as big
(supposing their bodies to be round) as the sphere ABGC.
But now I perceive a third sort of little animalcule, like
the point F, whereof I judge the axis to be only a tenth
part of that of the supposed animalcule E; wherefore
1000 animalcules such as F are as big as one animalcule
like E. This number, multiplied’ by the one foregoing
[110592], then makes more than 110 million little animals
[like F] as big as a sand-grain.
12 10 a 1728
12 10 + 64
144 100 16 6912
12 10 4 10368
288 1000 64 110592
144 1000
1728 110592000
Otherwise I reckon in this fashion’: Suppose the axis
of Fig. Fis 1, and that of Fig. EK is 10; then, since the
axis of Fig. D is 4 times as great as that of Fig. EH, the
axis of D is 40. But the axis of the big sphere ABGC is
12 times that of Fig. D; therefore the axis AG is equal
to 480. This number multiplied by itself, and the pro-
duct again multiplied by the same number, in order to
get the volume of ABGC, gives us the result, as before,
that more than 110 million living animalcules are as big
as a grain of sand:
1“ vermenigvuldig,’ in printed version, is a misprint. The MS. has,
correctly, vermenigvuldigt. ;
2 So in printed version. The MS. has merely Of anders (Or otherwise).
204 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
axis of Fig. F = 1
axis of Fig. H = 10
+
axis of Fig. D = 40
12
80
40
axis AG = 480
480
38400
1920
230400
480
18432000
921600
110592000
However, when I took somewhat coarser sand, as I did
when I drew up my estimate, I had to say that 20 axes
of the foresaid | biggest] animalcules did but make up one
axis of a sand-grain; and again, 5 axes of the lesser
animalcule equalled the axis of the first; and further,
10 axes of the smallest creature equalled one axis of the
second. In fine, then, according to this calculation, a
thousand million living animalcules are as big as a coarse
sand-grain (taken from fine scouring sand).
1 = axis F
10 = axis E
5
50 = axis D
20
1000 = axis AG
1000
1000000
1000
1000000000
LETTER 71. 7 MARCH 1692 205
In Leeuwenhoek’s next communications we find no further
mention of either protozoa or bacteria until we come to his
Letter 71, which, while recording various other observations,
contains the following words: '
I have by me the following notes, which I feel
constrained to add.
For several days past I have kept in a clean glass, in
my closet, some rain-water, gotten from a rain-cistern ;
in which water there was a little red worm,’ which I
divers times observed, by reason of its curious structure.
In this water, after a day or two, a multitude of little
living creatures did propagate themselves, they being of
two sorts which you commonly find in fresh or sweet
waters. The bigger sort I judged to be so small, that
thirty thousand of them together would scarce make up a
body as big as a coarse grain of sand.
On several different days I did look upon these little
animals,* and for so long, that not alone my eyes, but my
very hands, got a-weary ; and this was simply because I
did perceive such a plenty of these little animals, which
were coupled together, and so long remained in this pos-
ture: and I observed how the bigger sort dragged the
little ones along, or swam forward with them, with the
help of very plentevous feet, wherewith these animals are
furnished withal ; so that 1 was thus able on this occa-
sion to observe the copulation of these little animals
clearer than ever before. Nay, I saw them as plain as
you can see flying creatures* a-copulating before your
naked eye.
* Letter 71. 7 March 1692. To the Royal Society. MS.Roy.Soc.
Printed in Brieven, Derde Vervolg, p. 396 (the passage here translated
beginning on p. 423): Opera Omnia, Vol. II, p. 239 (1st pagination). A
partial English translation was also published in Phil. Trans. (1694),
Vol. XVIII, No. 218, pp. 194-199; but the passage here given in full is
there so abridged that it occupies only 84 lines (on p. 198).
> Rvidently a “ blood-worm’”’ (larva of Chironomus).
* The animals referred to are evidently ciliates.
* i.e. insects—not birds.
éé
206 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
These observations caused me to view more nicely the
lesser animalcules that were also swimming about in the
water, and whereof the number was a good twenty times
as many as that of the little animals aforesaid. Some of
these animalcules were also coupled; and I saw that
these likewise not only stayed long a-copulating, but also
that one of the pair, whether it swam through the water
or ran upon the glass, dragged the other one forward, or
trailed it after itself.
The foregoing passage is of great interest, since it is
evidently a record of observations made upon the conjugation
or fission of ciliates. In my opinion the evidence is in favour
of the view that Leeuwenhoek, on this occasion, witnessed
both these phenomena; though it is regrettable that he
gave so brief an account of what he saw. I cannot help
thinking that what he interpreted as “one animalcule
dragging another one along’ was a conjugating pair; whereas
‘one animalcule trailing another behind it”’ was really an
organism dividing transversely into two. Later,’ as we shall
soon see, he described the conjugation of ciliates in unmistak-
able terms.”
In a letter written some 3 years afterwards, Leeuwenhoek
mentions the discovery of “animalcules”’ in a new situation.
After describing his observations on the oyster, and its
generation, he remarks * :
I also paid attention to the ordinary water that is in
the shells of oysters; and I discovered therein a great lot
of little animalcules, which, in bigness and figure, were
like the little animalcules that you generally find in
canal-water, rainwater cisterns, and common ditch-water.
These animalcules were, in my judgement, above five
hundred times smaller than a young oyster.
' Cf. also the earlier observations in Letter 33, p. 200 supra.
> Letter 96, p. 213 infra.
* Letter 92. 15 August 1695. To Frederik Adriaan, Baron van Rhede.
Published in Brieven, Vijfde Vervolg, p.114: Opera Omnia, Vol. II, p. 511.
No MS., and not in Phil. Trans.
LETTERS 92 AND 96. 1695 207
No doubt these animalcules were protozoa: and it should
be mentioned that Leeuwenhoek had recorded a similar
observation at an even earlier date. Writing to the Royal
Society about fifteen years before, he mentioned’ that he had
found “ divers kinds of little living animalcules”’ in the juice
of mussels and oysters: but he gave no further account of
them, and it is impossible to ascertain what sort of organisms
these were. It should also be noted here, however, that in a
much later letter* he expressed the opinion that some of the
‘“animalcules”’ which he thought he saw formerly in the juice
of oysters were probably not really organisms at all, but
“particles”? set in motion by the cilia on the tissues of the
molluse.®
Leeuwenhoek’s last recorded observations on the “ animal-
cules” in infusions are contained in a letter written several
years later, and sent not to the Royal Society but to the
Elector Palatine. This very interesting letter runs as follows’:
In my letter of 18 September’ [1695] I ventured most
respectfully to describe how I opened a Freshwater
Mussel° and took out of it the unborn young mussels,’
* Letter 30. 5 April 1680. To Robert Hooke. MS.Roy.Soc. Published
in Brieven, Vol. I, p.33 (1st pagination): Opera Omnia, Vol. I, p. 25 (2nd
pagination): English abstract in Phil. Trans. (1693), Vol. XVII, No. 196,
p. 593.
* Letter dated 10 June 1712. To the Royal Society. MS.Roy.Soc.
English version printed in Phil. Trans. (1712), Vol. XXVII, No. 336, p. 529.
Not published elsewhere, and not numbered by L. himself.
* It seems to me probable that L. was here referring to the observations
contained in Letter 30, and not to those in Letter 92, which appears to record
a genuine observation of protozoa.
* Letter 96. 9 November 1695. To the Elector Palatine. Published
in Brieven, Vijfde Vervolg, p. 156: Opera Omnia, Vol. II (Contin. Arc. Nat.),
p.30 (2nd pagination). Not translated by Hoole. No MS., and not in
Phil. Trans. I translate the whole letter, with the exception of a few
immaterial words at the beginning and end.
° Letter 95, printed immediately before the present letter in L.’s published
works.
* Veen-Mossel (literally ‘‘ fen-mussel’’) — Anodonta: not easily recog-
nizable in the Latin version, where it is called “ concham ex genere earum
quae ex fossis capiuntur.”’ Veen means not only a fen, marsh, or bog, but
also the peat which can be dug out of such places: and consequently Hoole
(Vol. I, p. 85 sq.) translates veen-mossel as ‘ peat-muscle.’”’ But Anodon was
never known by this name in England—so far as I am aware.
" i.e., the “ Glochidia ’”’ larvae—described and figured in Letter 95.
208
cc
LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
which had developed so far that I judged them to be com-
pletely formed, because their shells seemed to be perfect.
I took several thousand of these unborn mussels, and
put them in a glazed white earthenware basin, and forth-
with poured canal-water upon them, in order to see
whether any of these unborn mussels would remain alive
and grow bigger.
Having put these little unborn mussels in the water,
I viewed them on several successive days, yet I could
make out no change in their size. But since, owing to
the rain which had fallen plentifully, our canals were
filled at that time with no other water than what runs
off the land, and which must then flow through our Town,
I saw, beyond my expectations, a great many very little
living animalcules, of divers sorts and sizes, in this water,
a-swimming among the unborn mussels. Amongst others
I saw some little worms,’ having a figure very much like
those worms that children void in their stools,” but whose
thickness I judged to be a quarter of that of a hair off
one’s head.
Furthermore, I saw some animalcules stuck fast to
one another by their long tails*; and these animalcules,
as well as sundry other sorts, I had never seen before, and
their motion was uncommon pleasant to behold.
Further, I saw that these animalcules did increase in
numbers from day to day.
At first, after four or five days, I replenished the water,
wherein these unborn mussels Jay, in such a fashion
that I poured off all but about a spoonful* of it, and then
presently added more canal-water again thereto.
1
Probably free-living nematodes.
* Probably meaning the nematode Oxyuris (=Enterobius) vermicularis.
3
Evidently a colonial Vorticellid (Carchesiwm ?). The “ animaleule with
a tail” is L.’s name for Vorticella, already described in Letter 18 (p. 118).
Further observations on the colonial forms are recorded later in the present
letter. (See also p. 277 sq., infra.)
* op een lepel vol water na Dutch version omnem fere aquam Latin
translation.
LETTER 96. 9 NOVEMBER 1695 209
In these my inquiries, I imagined that the unborn
mussels got eaten up by the little animalcules aforesaid ;
because it oft-times happened that I saw a multitude of
little animalcules that had got between the shells of the
young mussels, so that I judged, indeed, that I could even
see as many as fifty animalcules inside a single young
mussel. And during my observations, I observed that the
fishy matter in the unborn mussels got less from day to
day; nay, to such an extent even, that after the lapse of
twelve days, little or no fishy matter was to be discerned
between their little shells, which had become all trans-
parent. After this time, too, I could not perceive that
the animalcules were increasing in such great plenty.
My notion that the little animals were partly the cause
of the unborn mussels being eaten up (though ten
thousand of the little animals aforesaid would, for the
most part of them, scarce equal in bigness one of the little
mussels), was confirmed when I came to inspect the little
mussels (at the time when I had placed them in water in a
white Delft porcelain basin) after inclosing them in various
little glasses*; whereupon I perceived that each little
mussel inclosed in the little glass, though also lying in
water, still had its fishy substance between its shells,
notwithstanding that many of them had their shells wide
apart, or agape.
I have sometimes been puzzled when beholding the
multitude of little unborn mussels which lay inclosed in a
big mussel ; for I was not able to conceive why our canals,
and fens, are not overflowing with mussels, seeing that the
water does not run so strong that it could carry the little
mussels along with it, while they are still very small ;
and in the second place, seeing that they are not gathered
to serve as food: so that one mussel ought to beget
thousands. But now, after discovering how the little
" As mentioned below, these “little glasses” (glaasjens) were capillary
glass tubes, such as L. commonly employed in his experiments.
14
210 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
animals aforesaid devoured them, methought this a
sufficient reason why freshwater mussels are not found in
ereater plenty.’
After this, I let the water stand for twelve more days,
without replenishing it, in order to see whether, if I did
so, the animalcules would multiply in greater numbers.
But I perceived that the animalcules decreased from day
to day; so that by the 8th of October they were indeed
grown so few, that where I had before discovered a good
hundred of them, I now could scarce see one; and those
of the biggest sort, which still remained over, moved
forward very slow, and were very thin in the body; and
all the little shells of the unborn mussels had so far
increased in transparency, that I could make out some
hundreds of very little parts, whereof they were composed.
And so, from all these observations, I concluded that
all the various animalcules had now died for lack of food.
In order to satisfy myself further concerning the
plentevous multiplication of the little animalcules, and
in so very short a time, I took a parcel of canal-water,
somewhat more than a common wine-glass full, and put
in it an ordinary mussel, that I had taken out of its shell’ ;
and I put this mussel in the water to see, if ’twere
possible, whether the animalcules would multiply beyond
what they commonly do, owing to the food that they
would be able to get from the mussel.
After the mussel had lain for four-and-twenty hours in
the water, I took a little of the uppermost part of the
water, and examined it through the microscope; and I
' From these observations one can hardly doubt that L. had got
something more than an inkling of the part played by putrefactive micro-
organisms in the general oeconomy of nature. To appreciate the novelty
of this notion—nowadays commonplace— one must remember that it belongs,
historically, to the nineteenth century.
? In such an infusion of freshwater mussel many different Protozoa are
commonly found, including ciliates (e.g., Paramecium) and flagellates (e.g.,
Trepomonas). For this reason it is impossible to determine what particular
forms L. was likely to have seen.
LETTER 96. MUSSEL-WATER ik
saw, to my wonder, a vast number of animalcules. And
after the water, with the mussel in it, had stood for twice
twenty-four hours, I observed that the number of animal-
cules was greatly increased. I took a little of this water,
and put it in a glass tube, whose diameter was about
a fifteenth of an inch, and which was filled for about an
inch of its length with the water. In this water I saw a
few little animalcules swimming, whereof several thousand
together would scarce equal a sand-grain in bigness.
These animalcules had a pretty structure, for the round
circumference of their bodies seemed to be made up of ten
or twelve brighter round pellets, while in the middle of
them there seemed to be a little dark spot, somewhat bigger
than the pellets. These animalcules generally rotated
themselves in their progression (which took place
slowly).
When these animalcules had been a little while in the
foresaid glass tube, I saw a slender little structure like
unto a little branching vein, with seven or eight lesser
branches, each several little branch being full a hundred
times thinner than a hair off one’s head; and at the same
time I saw that at the utmost extremity of every little
branch, one of the forementioned little animals was firmly
fixt, though at first I could discover no motion in ’em.
Yet after the lapse of about a minute, I perceived that
some animalcules began to move themselves to and fro,
whereby each of the thin little branches became bent
into divers coils. The longer this motion continued, the
stronger it became, till at last the little creature, by its
efforts, got loose from the little branch, and swam off;
and the same thing came to pass with all the others too,
so that the little branching structure was forsaken by all
the animalcules that were discernible.”
i T
’ Probably ciliates—the bright bodies being food-inclusions, and the dark
central spot the meganucleus.
* This graphic narrative gives an unmistakable description of Carchesvwm.
212
1
ce
LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS ”’
From this spectacle, I imagined that the little animals
of this kind must have laid their little eggs, or young
animalcules, upon the ends of every little branch, and
that they had there waxed in bigness, and grown up.
Furthermore, this little branching vein was for the
most part clothed with a clearer matter, which I judged
was made up of round pellets. Seeing this, it came into
my head that all the round particles which I could see
might perhaps be really eggs, or young animalcules, and
that from these particles, moreover, similar animalcules
might presently come forth. After the lapse of another
twenty-four hours, I looked upon the little branch again ;
and I then saw that some animalcules, which had reached
their full growth, were fixed anew upon it; and that
many of these animalcules were swimming around the
little branch, while the roundish particles, that I’d seen
on the branch the day before, were much diminished in
number.’ ;
At a distance of about half an inch from the little
vein-branch aforesaid, there lay in the water a little fibre,
whereon were also fixed some little animals; and these too
were come forth (so I imagined) from the round corpuscles
which were likewise fixed to the fibre. These animalcules
were increased to such great numbers in the space of
twice twenty-four hours, that I now saw quite fifty of
them where I had before seen but one.
Now, as we have made sure that, in twice twenty-
four hour’s time, animalcules appear, which have reached
their full growth; and as we imagine that they have
come forth from little round particles: therefore, we need
not wonder at the multifarious little animalcules which
we perceive to be bred in water in only a few days’ time
(provided only that food be not lacking for them). And
who knows but what one sort of these very little water-
The observations here recorded were, no doubt, perfectly accurate :
but the interpretation which L. put upon them is, of course, incorrect.
LETTER 96. MUSSEL-WATER 213
creatures may not gobble up another sort, using it as
food,’ just as we see that big fish do? For, an ’twere
otherwise, the water would get stuffed full with little
animalcules.
One day afterwards I looked at the animalcules again,
and saw, to my wonder, that many of ’em were coupled;
nay, some of ’em even coupled before my eye; and at the
beginning of their copulation they had a wobbling motion,
but after coupling swam forward together, and did stay
still too, fixt to the glass.’
At this time I saw also that the bodies of each animal-
cule of the pair were of a roundish figure ; for no matter
how they turned about in swimming forward, they always
kept one and the same shape, looking like a little round
cluster of grapes, the cluster being stuck together very
tight; and as the animalcules swam forward, you saw each
of the supposed grapes in motion.
"Twas eventide when I carried out the observations
last mentioned; and next day, in the morning, I found
that many of the animalcules were dead, and by evening
they were so diminished, that I could find but four of
them that were still alive: wherefore I concluded, that the
little creatures were died off for want of food. After
another night had passed, I saw but one animalcule living ;
and the bodies of all the dead animalcules in the water
were so gone to pieces, that I saw nought but little round
particles (as they seemed to my eye), which made the
water, wherein these little animals had been swimming,
all troubled.
' As the “ bigger sort’ were, in part, ciliates, while the “smallest sort ”’
were bacteria, L.'s conjecture here was perfectly sound.
* This passage proves conclusively that L. observed the conjugation of
ciliates. In his earlier observations he had only seen the organisms joined
together; and consequently he may have seen ciliates really undergoing
fission—not conjugating. But here he says he actually saw them come
together, so that there can be no doubt as to the correctness of his
interpretation.
214 LEEUWENHOEK AND HIS “LITTLE ANIMALS”
Two days after the foregoing discoveries, I again beheld
the small parcel of water aforesaid in the glass tube; and
as I did so, I saw a huge number of extreme small fishes,
or animalcules, which I may call little eels,’ because in
swimming forwards they lashed their bodies like eels
do, and so quick that ’twas marvellous. These little fish
did mostly stay close beside one another, and round the
circumference of the tube, and in vast numbers; and in
my judgement their length was equal to the diameter
of one of those blood-globules which make the blood red.
And they remained alive some seven days, after which
time I could make out only one every now and then.
Among these little animals, or little fishes, I did also
see a-Swimming a few smaller animalcules, whereof I
deemed that eight of ’em together were no bigger than
the said blood-corpuscle*: and now I could no longer
discern that little structure that I heretofore likened to a
little branching vein, how oft soever I looked for it.
These last-mentioned animalcules were so prodigiously
increased in two or three days, that ‘tis incredible ; though
by now half the water was evaporated away.
All the water that I have so far spoken of, which I had
put in the glass tube, and wherein the foresaid multi-
plicity of little animalcules were bred, I deemed (to the
best of my knowledge) to be no more in bulk than the
eighth part of a green pea; but not being content with
this my estimate, I went and weighed a like quantity of
water, and I found its weight two grains. I did also
weigh some peas, and found that a common pea weigheth
eight grains.
Through the microscope with which I had carried out
the first observations, I imagined I still saw,* in water
* Probably Spirilla—certainly bacteria of some sort.
* i.e., their diameter was about half that of a red blood-corpuscle.
Undoubtedly bacteria.
° L., it will be recalled, commonly used a different microscope for each
separate observation—the object being more or less permanently fixed and
focussed before the lens.
LETTER 96. MUSSEL-WATER 215
taken from the surface of that wherein the mussel lay, a
vast company of living animalcules: but to make sure of
this, | made use of a glass of higher magnification, and
a different instrument: and I then saw so great a many
of such extreme small animalcules,’ that there’s no man
living could possibly conceive of them; nay, they were so
little, that several millions of them together would not be
as big as a coarse grain of sand. Nevertheless, all these
animalcules, when I put them in a glass tube, remained
alive but a little while.
Moreover, I found that the animalcules in the water
that the mussel was in, had increased so much in seven
or eight days, that I might well say their number was (to
the best of my judgement) quite ten times a hundred
thousand more than those in the water before I put the
mussel in it.
Regarding this increase of animalcules in water, and in
so very short a time, I have oft-times been amazed: and
especially, because I chanced to see divers sorts of
animalcules, which increased in numbers, without being
able to discern any of them that were smaller; all of
them being of an equal bigness.”
But after observing what I have just related (namely,
that there are animalcules which do not take to swimming
about till they have reached their full growth, and
which soon after are ready to copulate; and therewithal
that a full-grown animalcule is produced in one night), I
was now, to my great satisfaction, delivered from all
those difficulties, that I had for years laboured under,
concerning the generation of these little creatures.
When I first discovered, in the year 1675, a great
plenty of divers very little animalcules in water, and
made these observations known by letter to the Royal
’ Bacteria.
* He means that he could detect no young ones of any species.
216 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ’”’
Society in London, neither in England’ nor in France
could they accept of my discoveries: nor do they even yet
in Germany, as I’m informed.
This remarkable document ends at this point with a couple
of extracts from Leeuwenhoek’s letters of 23 March 1677 (to
Oldenburg) and 5 October 1677 (to Lord Brouncker), which
were sent to the Elector Palatine “to give him greater
satisfaction concerning the vast numbers of little animalcules
that are found in water”: but as these letters have already
been given fully on earlier pages,’ it is unnecessary to repeat
them here.
With these observations we come to the end of Leeuwen-
hoek’s researches on the free-living Protozoa and Bacteria, in
so far as they were made in the XVII Century. Later he
made many notable additional observations, but these will be
chronicled in a later chapter: and we must now retrace our
steps in order to record his equally wonderful discoveries
concerning the parasitic Protista.
* This can hardly be regarded as a fair description of the reception
accorded to L.’s earliest observations by the Fellows of the Royal Society.
* Vide pp. 168 and 173 supra. The second letter was originally addressed
to Oldenburg, but redirected to Brouncker when L. heard of his death.
217
CHAPTER 3
THE FIRST OBSERVATIONS ON ENTOZOIC
PROTOZOA AND BACTERIA
(Lerters 7, 33, 34, 38, 39, 75, 110, etc.)
E have already seen (in Chapter 1) how Leeuwenhoek
NV discovered the free-living Protozoa and Bacteria.
We inust now chronicle his discoveries in the world
of similar “ parasitic’ organisms.’
It will be remembered that Leeuwenhoek first saw protozoa
in water in the summer of 1674.* He probably first saw a
parasitic protozoon—though he had no idea what it was—in
the autumn of the same year. Whilst examining the bile of
various animals, he hit upon some curious structures which he
described, in the course of a rather rambling letter, in the
following terms: *
The bile of a cow was examined* by me on the Ist
instant,’ and therein I beheld some few globules” that
floated in the liquid ; but I didn’t see them unless I set the
bile in a continual motion before my sight, for ’twould else
have been impossible for me to perceive the globules in it,
* To call all such micro-organisms studied by L. by the opprobrious
name of © parasite” is hardly justifiable, for most of the forms which he
described cannot be regarded as harmful. They are “ parasitic” in a
colloquial and unscientific sense only.
” See p. 109.
> From Letter 7. 19 October 1674. To Oldenburg. MS.Roy.Soc.
This letter was wholly unpublished until recently, when I first published
(Dobell, 1922) the passages given here in revised translation.
* i.e., with the microscope.
° 4.e., 1 October 1674.
° clootgens MS.
218
~
LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
because they were so few in the bile that I was examining.
But afterwards, examining the bile of another cow, I
found that the globules were of a heavier matter than the
liquid that they floated in; wherefore I drew off the bile
from the bottom of the gall-bladder, and then found that
there were' many hundred times more globules in this
bile than in that which I had taken from the upper part
of the gall-bladder; and there were, besides, some
corpuscles * which, to my eye, looked as big as ants’ eggs.”
These had the figure of an egg,* only with this difference,
that whereas an egg is more sharply pointed at one end
than at the other, yet these corpuscles were equally
pointed at both ends: and moreover these corpuscles
were composed of globules joined together, and had a
yellow colour, except several which were somewhat
whitish ; but notwithstanding, they were so transparent
that you could see the body of one through that of
another. And this transparency making me wonder
whether they might not, in fact, be little vesicles filled
inside with liquid, I fished some of these corpuscles out of
the bile with a fine hair; and looking at ’em on the hair,
I perceived two which seemed to be pushed in, just as
though you had blown up a bladder and then stuck your
thumb in it, so as to make a dent in it; whereupon I was
the more firmly persuaded that these corpuscles were filled
with some sort of humor. Afterwards, on examining
more biles from oxen, I found them the same as before;
only with this difference, that one bile might be furnisht
with more of the oval corpuscles than another.
was MS.
* deeltgens MS.
8
L. means that the objects looked, under his microscope, about as big
as ‘ants’ eggs” look to the naked eye. At a later date he published a
remarkable account of ants, from which it is clear that he was well aware
that
the ant’s “egg” is not really an egg, but a pupa. See Letter 58,
9 Sept. 1687.
4
: )
2.€., a hens egg.
LETTER 7. 19 ocToBER 1674 219
In the bile of two calves I find, furthermore, some very
little globules floating, and very many irregular particles
of divers forms; among others, some like little floating
clouds, all consisting of very little globules joined together.
On seeing these irregular congealed particles, I judged
them to be joined or stuck together through no other
cause than because the bile had got cold, and was without
motion. In the bile of a third calf there wére a few oval
corpuscles.
Moreover, in the bile of sucking lambs I find there are
very little globules, and some, though very few, bright
particles, which are a bit bigger; besides irregular particles,
of divers figures, and also composed of globules clumped
together.
The bile of a yearling sheep I find to be like that of
sucking lambs, only with this difference, that in this bile
there are also oval corpuscles of the bigness and figure of
those that I remarked in ox-bile.
I have examined the bile of two young rabbits: that of
the first was inclined to a purple colour, and in it I beheld
very many globules, and irregular particles made up of
globules clumped together, which were of various red
colours:* and this diversity of colour I imagined to be
due to no other cause than that some of these compound
particles, being made up of more globules, were denser
than the rest. In the other bile the irregular particles
were fewer, but there were more globules and the colour
was a light reddish.
Further, I examined the bile from three old rabbits.
The first had a very few small globules, but very many
oval corpuscles of a figure like those that, as I have said,
I saw in the bile of a cow. In the bile of the two other
rabbits there was nought but globules, and irregular
* Evidently red blood-corpuscles. LL. had described these—from his
own blood—in another letter written earlier in the same year (Letter 3,
7 April 1674). An English abstract of this appeared in Phil. Trans. (1674),
Nol. EX. No. 102. pn. 23:
‘é
220 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
particles made up of globules joined together; though
the thin matter’ of one was much thicker and stickier
than that of the other, and there were some little clouds
floating through it.
I have furthermore examined the biles of fowls,
turkeys, ete., and in them I also found very little
globules floating, and irregular particles composed of
globules stuck together.
I think there can be no doubt that the “ oval corpuscles ’”—
called eyronde deeltgens in the original—which Leeuwenhoek
discovered in the gall-bladder of one of his “ three old rabbits,”
were the oocysts of the coccidian Himeria stiedae; while the
comparable structures which he found in the bile of sheep and
oxen were, equally certainly, the eges of trematodes.” But as
I have already discussed this subject in some detail elsewhere,’
I shall say no more about it here. If my interpretations be
correct, then the foregoing extract records the first observations
ever made upon the Sporozoa or upon any parasitic protozoon.
It is true that Leeuwenhoek himself did not realize that he
had discovered a stage in the life-history of a brand-new kind
of parasite: but the same can be said also of others who are
now generally credited with the discovery of the Coccidia.'*
The fact remains, none the less, that he saw and described—
though his description was not published for nearly 250 years—
a coccidial parasite long before all other men.
* i.e., the liquid part of the bile.
* Fasciola hepatica—the worm itself—was well known to L.; for the
Dutch anatomist Bidloo (1649-1713) dedicated a little memoir to him, in
1698, in which it was described and figured. At a later date, L. himself
wrote a letter to the Royal Society on the ‘ Worms observ’d in ae
Livers ’’—of which an English abstract was published i in Phil. Trans. (1704),
Vol. XXIV, p. 1522. The original letter is extant, and is dated 3 Nov.
1703. It was not included in the Dutch or Latin collected works.
* See Dobell (1922).
“ The lesions of hepatic coccidiosis in the rabbit appear to have been
first depicted by [Sir] Robert Carswell (1793-1857 ; Professor of Pathological
Anatomy at University College, London) in the year 1838. He regarded
them as “the seat of tuberculous matter.” The oocysts of E. stiedae were
first figured and described in print by Dr Thomas Gordon Hake (1809-
DISCOVERY OF COCCIDIA AND LEPTOMONADS 221
Leeuwenhoek’s next observations on ‘ animalcules”’
inhabiting the bodies of other animals were written down
in 1680 and printed some few years later. ‘They occur in the
course of his description of the spermatozoa of insects—various
species of which he dissected in his attempts to study their
“seminal animalcules”. After recording some findings in
flies, he casually adds the following: '
I have also seen, in the summer,’ in a big horse-fly
(which was a female, out of which I pulled many eggs), a
lot of small animalcules ; though these were not a sixth
of the length of the animalcules aforesaid,* but a good 10
times thicker.* They lay mingled with the thin matter ”
that was in the fly’s guts, and moved forwards very
quick.
From the size and proportions of the “ animalcules”’ here
mentioned, and from their situation, it can hardly be doubted
that Leeuwenhoek actually saw on this occasion a protozoon
(or possibly a bacterium) in the gut of a horse-fly. The
dimensions of the organism are against the bacterial inter-
pretation, but agree very well indeed with the supposition that
he saw a Orithidia (or Leptomonas).° If this was so, then we
1895; a practising London physician, and English minor poet) in 1839.
He interpreted the lesions as “carcinoma”, and the oocysts as “a new
form of the pus globule.” See Dobell (1922).
* From Letter 38. 12 November 1680. To R. Hooke. MS.Roy.Soc.
Published in Brieven, Vol. I (Dutch), and Opera Omnia, Vol. II (Latin).
The full letter first appeared in print (in Dutch) in 1684. An incomplete
English translation was published earlier, however, in Hooke’s Phil. Collect.
(No. 3, pp. 51-58; 1681). The passage here translated is on p. 23 of the
Dutch printed version.
* Presumably 1680.
° L. here refers—as the context shows—to the spermatozoa of “ the
smallest sort of our common house-fly.”’
* On L.’s system this means that they had rather more than thrice the
diameter of the fly’s spermatozoa.
° 4.e., liquid or watery material.
° These flagellates oceur—as is now well known—in many different
species of Tabanidae. Several species of Crithidia have been described, in
recent times, from the intestines of HKuropean species of Tabanus.—I may
add that, forty years ago, Biitschli (1887-89; Vol. III, p. 1101) pointed out
that the organisms here described by L. were probably flagellates; but he
wrongly dated the observations 1695—the date of publication of the first
Latin translation.
222 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
have here the first recorded observations ever made upon any
protozoa belonging to the important flagellate family of the
Trypanosomatidae. But this interpretation, though very
plausible, is not absolutely certain ; for the details recorded
are obviously too scanty to warrant dogmatic deductions.
Nevertheless, it can, I think, be concluded—with complete
assurance—that Leeuwenhoek observed “ parasitic” protists
of some sort in the intestine of a horse-fly as early as the
year 1680.
We now come to a letter of great historic interest and
importance—a letter which has rarely been read aright, but
one which records in no uncertain terms the discovery of the
intestinal protozoa and bacteria of Man. This letter was
written in 1681, and in it Leeuwenhoek discusses a variety of
subjects—such as the structure and falling-out of the hair,
“blackheads ”’ (comedones), clay, and gout: but the only part
which here concerns us deals with the discovery of “living
animalcules in the excrements.” ‘The passages in question
run as follows:'
I weigh about 160 pound, and have been of very nigh the
same weight for some 30 years,” and I have ordinarily of
a morning a well-formed stool; but now and then hitherto
I have had a looseness, at intervals of 2, 3, or 4 weeks,
when I went to stool some 2, 3, or 4 times a day.’ But
* From Letter 34. 4 November 1681. To R. Hooke. MS.Roy.Soc.
Published in fullin Brieven, Vol. I (Dutch), and Opera Omnia, Vol. I (Latin).
The Dutch version first appeared in 1686 (Ontled. en Ontdekk.), the Latin
[from which the date of the letter was omitted ] in 1687 (Anat. s. Int. Rerwm).
An English abstract was published by R. Hooke in Phil. Collect. (1682),
No. 4, p. 93: and another by Derham in the posthumous Phil. Expts. and
Obss. of Hooke (1726), p. 61. The letter itself was presented to the Society
at their meeting held on 2 Noy. 1681, and read in English translation at the
following meeting on Nov. 9 [O.8.]. Cf. Birch, Vol. IV, pp. 99, 101. Part
of this letter was also translated by Hoole in his Select Works of L.—but
not the part with which we are now concerned. I have already translated
and commented upon the paragraphs dealing with intestinal protozoa
elsewhere (Dobell, 1920).
* When he wrote this L. was 49 years old.
* The Latin version of this passage is somewhat ambiguous, and has
apparently led some readers to suppose that L. frequently suffered from
diarrhoea lasting for 2-4 weeks at a stretch. It has even, indeed, given rise
to the belief that he suffered from chronic dysentery for 30 years. His own
words do not countenance any such conclusions. Cf. Dobell (1920).
LETTER 34. 4 NOVEMBER 1681 293
this summer! this befell me very often, and especially
when I partook of hot smoked beef, that was a bit fat,” or
ham, which food I’m very fond of; indeed, it persisted
once for three days running, and whatever food I took, I
kept in my body not much > above 4 hours; and I
imagined (for divers reasons) that I could get myself well
again by drinking uncommon hot tea, as hath happened *
many a time before.
My excrement being so thin,’ I was at divers times
persuaded to examine it ;° and each time "T kept in mind
what food I had eaten, and what drink I had drunk, and
what I found afterwards*: but to tell all my observations
here would make all too long a story. I will only say that
I have generally seen, in my excrement, many irregular
particles of sundry sizes, most of them tending to a round
figure, which are very clear and of a yellow colour :’ these
were the ones that make the whole material look yellow
to our eye. And there were also, besides, suchlike
particles that were very bright and clear, without one
being able to discern any colour in them.”
I have, moreover, at divers times seen globules that
were as big as” the corpuscles in our blood, and that each
a
" i.e., anno 1681.
2
dat een weynig vet was. These words are in the printed version but
not in the original MS.—A similar remark is made by L. much later in
Send-brief XX XIX, 13 July 1717, to J. G. Kerkherdere.
3
veel is here in the printed letter, but not in the MS.
‘ is gelukt [=succeeded] MS. is geschied [ =befell] printed version.
> 7.e., dilute or watery.
6
7
8
9
i.e., with the microscope.
soo nu en dan MS. soo nu als dan printed version.
This word is not in the originals. I add it to preserve the sense.
Probably incompletely digested remains of meat (striated muscle).
0 fe., the faeces en masse.
11 Pyobably fat-droplets.
12 The Latin version mistranslates soo groot als as ° bigger than”
(globulos globulis nostra sanguinis majores vidi).
224 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
of them was made up of 6 separate globules :' and further,
there lay, among all this material, globules whereof 6 of
‘em together would make up the bigness” of a blood-
corpuscle. These last were in such great® plenty, that
they seemed to form a good third of the whole’ material:
while there were besides many globules which were so
small, that six-and-thirty of ’em would make up the bigness
of a blood-globule.’
All the particles aforesaid lay in a clear transparent
medium, wherein I have sometimes also seen animalcules °
a-moving very prettily; some of ‘em a bit bigger, others
a bit less, than a blood-globule, but all of one and the
same make. ‘Their bodies were somewhat longer than
broad, and their belly, which was flatlike, furnisht with
sundry little paws, wherewith they made such astir in the
clear medium and among the globules, that you might e’en
fancy you saw a pissabed‘ running up against a wall; and
albeit they made a quick motion with their paws, yet for
all that they made but slow progress. Of these animalcules
I saw at one time only one in a particle of matter as big
as a sand-grain; and anon, at other times, some 4, 5, or
even 6 or 8. I have also once seen animalcules of the
same bigness, but of a different figure. *
* At one time L. held the curious belief that each red blood-corpuscle
was composed of 6 aggregated smaller “globules”. This was an error
probably due, I think, to misinterpretation of diffraction-images.
* i.e., in volume—not in diameter.
* groote stands here in the MS. but not in the printed letter.
* gantsche MS. omitted from printed letter.
° 7.e., their diameter was between + and + of that of a human red
blood-corpuscle.
* The following description—as I have elsewhere tried to show (Dobell,
1920)—is a graphic account of the flagellate Giardia (=Lamblia)
intestinalis.
" The woodlouse or sow-bug (Oniscus asellus). The Latin translation of
this passage has given rise to many curious misunderstandings. Cf. Dobell
(1920), where “ pissabeds”’ are more fully discussed.
* As no other details are given, it is impossible to identify these
organisms. Possibly they were Trichomonas or Chilomastiz.
INTESTINAL PROTOZOA OF MAN DISCOVERED 225
I have also seen a sort of animalcules that had the
figure of our river-eels: these were in very great plenty,
and so small withal, that I deemed 500 or 600° of ’em
laid out end to end would not reach to the length of a full-
grown eel such as there are in vinegar.” These had a
very nimble motion, and bent their bodies serpent-wise,
and shot through the stuff as quick as a pike does through
the water.’
At another time I saw, in 4 several observations, but
one animalcule of the sort first spoken of;* but at my
fourth observation, observing more narrowly than before,
I saw a great number of animalcules,’ each of which I
judged to be more than 200 times less than a globule of
our blood: for I imagined that I could make out that the
length of six diameters of one animalcule couldn’t reach
beyond the diameter of one blood-globule. But here I
speak to those who are versed in geometry, and know full
well that if the diameter of one body be 1 and that of
another (of like figure) be 6; then the difference in their
bulk is as 1 to 216. And I can’t forbear to say that I
have divers times judged that I have seen, with great
delight, in a particle of matter of the bigness of a coarse
sand-grain, more than 1000 living animalcules, and these
of 3 or 4 sorts, all alive together; nay, you might well
have supposed that the whole material consisted of nought
but living animalcules. Some people hearing this might
cme EUS USSU
* The Latin version wrongly says “50 or 60” (quinquaginta aut
secaginta), which would—if correct—-put a very different complexion on
this passage.
> Anguillula aceti, the “ vinegar-eel’’. Cf. p. 150 swpra.
? From the description here given, it can hardly be doubted that these
organisms were spirochaetes. In recent years a vast literature has sprung
up on the intestinal species in man; but it must suffice to note here that
more than one species occurs in human faeces, and that spirochaetes of
some sort are normally present in the intestines of most human beings.
This is the first record of their occurrence.
* Referring to Giardia.
> Probably bacteria, but possibly inanimate particles in Brownian
movement.
15
226 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
perhaps imagine that these animalcules, because of their
extreme littleness, might well get through into our blood ;
but I conceive that the vessels which conduct the material
(out of which blood, fat, etc. is made) are so small, or must
pass through such narrow channels, that even if such a
little animalcule were divided into more than 1000 parts,
‘twould still be too big to get through them.’
I have, moreover, examined my excrement when it was
of ordinary thickness, and also mixed with clean water,
but could then discover no animalcules in it; but
whenever the stuff was a bit looser than ordinary, I have
still seen animalcules therein, contrary to my expectation.
I have, however, also seen in it some particles of food that
were not digested; among others, for example, after I had
eaten asparagus I saw very prettily its little tubes (off
which the soft parts had been all digested away).
At divers times in the summer I have betaken myself
into our meadows, and collected the dirt of cows and
horses, just as they let it drop; yet I could discover no
living animalcules therein, but most of this stuff (setting
aside grass-particles which were undigested) was made up
of globules, whereof 6 would be as big as a blood-globule,
and many lesser globules of which I judged that 36
together would be only as big as a blood-globule; all these
lying in a clear medium.
In the month of May,’ I rode my horse (which is a
mare) very hard, for about 1% hour’s going;° and on
getting back to the stable, she let go her urine; and as
the last of this urine looked to me very thick, and was
" L. means that the channels—in the intestinal wall—through which
the ultimate food-particles in the gut pass into the blood-stream are too
minute for bacteria to traverse them: and that even if a bacterium were
but a tenth of its length, it still would be too big to do so.
> Presumably anno 1681.
* 14 wre gaens MS. The printed version says “an hour and a quarter ’
(een en een quart van een ure). Apart from this discrepancy in the time, it
should be noted that L. does not mean that he rode his mare hard for an
hour and a half (a pretty strenuous feat), but for a distance equal to that
y
INTESTINAL PROTOZOA AND BACTERIA O27
of an ashen colour, I viewed it’ through a common
microscope, that I had by me; and I found that what
gave it the ashen colour were globule-like particles, of
sundry sizes, each of ’em made up of still lesser globules
stuck together. And these last globules were as big as
the globules of our blood, and each of these again consisted
of six several globules. I can’t describe the first sort of
globules better than by likening them to a round bunch
of grapes, growing very close together, as it looks to your
naked eye ; and although the particles were not perfectly
round, yet I may call ’em globules, for they were wanting
in nothing but that those which were as big as a blood-
globule (which I have already described as compound)
stuck out a bit on the outside, like each grape does from
its bunch.” Of this matter I took up a little, and found
that besides the globules aforementioned there were yet
many others, which had a sixth of the bigness of one of
our blood-globules, and also some whereof I judged that
36 of ’em together would only make up the bulk of a
blood-globule.°
which would be covered in an hour and a half by a man on foot. (Cf. note
3 on p. 109 supra.) The Latin translator—who copies the time from
the printed Dutch version, not the MS.—accordingly renders this phrase
(correctly) as “ circiter horam atque horae quadrantem pedestris itineris. . .”
' In an earlier communication (Letter 38, 12 Noy. 1680), L. mentions
that he examined his own urine, at a time when he was sick, and found in
it—in addition to numerous particles—several red blood-corpuscles (ef. p. 12
of Dutch printed version).
* This is a hard sentence to translate closely and intelligibly. I give it
as near as I can—without improving it too much.
* The foregoing observations—though they record the discovery of no
new animalcules—appear to me to be of great importance; for they show
that L. really recognized living bacteria when he saw them. He did not
here—or elsewhere—mistake minute inanimate particles for “‘animalcules.”’
At first sight it may seem strange that he did not take all minute moving
particles for living organisms—as would have been indeed excusable.
‘“ Brownian movement’ was not “ discovered ” until a century and a half
later: but the phenomenon itself must have been frequently witnessed by
L. He accounted for it as a consequence of the heat imparted to his
microscopic preparations by their proximity to his own body. (He had to
hold his microscopes very close to his face, because of the very short focus
of his lenses.)
228
1
LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
I then bethought me to examine the dirt of hens; and
in order to get it clean, I squeezed the dirt out of a fowl’s
body as soon as it was dead. On viewing it, I saw
therein a huge number of little snakes or eels, which I
considered to be the fowl’s seed; as indeed it was. For
the cock was more than half full-grown ;’ and I took it
for certain that in squeezing out its dirt, I had compressed
its seed-vessels so violently that I squeezed the material
out of them too. Afterwards I squeezed the dirt out of
the hind end of several young hens, but I didn’t discover
anything but one living animalcule, which was about as
big as a sixth of a blood-globule. The dirt consisted,
further, of a clear matter, mixed with very many globules
as big as a sixth of a blood-globule. These also looked as
though they were composed of 2, 3, 4, 5, or 6 globules
stuck together. And there were besides very many wee
globules whereof 36 together (so I imagined) would be
only as big as a blood-globule.
I also” gently pressed the dirt out of two new-killed
pigeons, that were about a month old; and in the first I
couldn’t find any living animalcules at all. But in the
dirt from the second pigeon (which was much clearer
than the first’s) I saw many animalcules;* so that I
judged there were quite 100 of ’em in a bit as big asa
sand-grain. ‘These moved among one another very
prettily *, and were all of one and the same bigness,
having the figure of an egg, and being in my judgement
as big as a sixth part of one of our blood-globules.
Beyond this, the stuff was like what I have described
above from hens.
half volwassen MS. volwassen printed version. I follow the MS.
because it is difficult to comprehend how the bird could have been “ more
than full-grown’”’. The Latin translator evaded the ambiguity by calling
the fowl “ major annis gallus’’.
* ook MS. omitted from printed letter.
* Bacteria of some sort, in all probability.
* seer aerdig MS. but the Dutch printed letter says seer vaardig [| =very
quickly] —which is concordantly rendered expeditissime in the Latin.
LETTER 34. INTERPRETATIONS 229
The foregoing quotations—which contain, I believe, all
that Leeuwenhoek ever wrote on such subjects—record a series
of truly remarkable discoveries; and they prove conclusively
that he discovered intestinal protozoa and bacteria in man
and several other animals. He here saw, and recognizably
described, the flagellate Giardia' and the Spirochaetes and
other Bacteria in his own faeces. He also, I think, must have
seen other human intestinal flagellates (possibly Trichomonas
or Chilomastix), though this is uncertain: but he certainly
saw bacteria in the excrement of a fowl and in that of a
pigeon, though curiously enough he failed to find them in the
dung of cattle and horses.
Some of the interpretations which have been put upon
Leeuwenhoek’s words in this connexion must be read to be
believed. As I have commented upon them elsewhere’ I need
say no more about them here. I will only note that the
passages just quoted supply all the evidence there is for the
statement—frequently met with in the literature—that
Leeuwenhoek described the ciliate Balantidium coli, and that
he himself suffered from dysentery caused by this parasite.
Beyond all doubt this is a literary fiction lacking all
foundation. Though an Austrian nobleman® assures us
that Leeuwenhoek could not have seen what he described,
and therefore what he saw must have been something totally
different ; and though a distinguished American medico‘* tells
us that when Leeuwenhoek says he had weighed 160 lbs. for
30 years and usually had solid stools, he meant that he had
suffered from balantidial dysentery since the age of 30: never-
theless, serious students of protozoology may well rest content
with the plain and obvious meaning of his own simple words.
Before we proceed to the next discoveries, it may not be
amiss to emphasize the novelty of those just recorded. At the
time when the foregoing observations were made, no protozoa
or bacteria of any kind were known—except the free-living
* Of. Dobell (1920).
* Dobell (1920).
* Stein (1867), Vol. II, p.321. Although I exposed Stein’s blunders
some years ago, I note that a recent German writer (Pritze, 1928) still
accepts them. But as he evidently overlooked my paper, and knows nothing
of L.’s work, I cannot take his opinions seriously.
* Strong (1904).
230 LEEUWENHOEK AND HIs “ LITTLE ANIMALS ”’
forms described by Leeuwenhoek himself a few years earlier.
No animal or “‘animalcule” smaller than a worm was known
to live inside the body of man: and the existence of hordes of
micro-organisms within the bodies of healthy animals was as
wholly unsuspected as it was unheard-of.
It is worthy of note, moreover, that neither here nor else-
where in his writings does Leeuwenhoek associate entozoic
protozoa or bacteria with the causation of disease. He found
them in normal hosts, and it probably never occurred to him
that any of them might have pathogenic properties. Having
no medical education, and no preconceived notions regarding
““animalcules,” he recorded his findings simply and objectively,
and it was left to others to elaborate his great discovery into
the vast present-day corpus of medical protozoology and
bacteriology. In a sense, therefore, he missed the great
practical implications of his revelation." But it must not be
forgotten that the micro-organisms which he studied were all,
in all probability, harmless; and consequently he deserves
every credit for not speculating in excess of his facts. If
every worker on the same subjects during the next 250 years
had possessed an equally conservative and scientific spirit, a
great deal of unnecessary confusion in our knowledge of
“microbes ”’ might have been avoided.
No further observations on entozoic protozoa were recorded
until 1683. But in this year Leeuwenhoek wrote another
highly interesting letter, in which he described many novel
observations on frogs and other animals. He here accurately
described, and discussed, the frog’s spermatozoa and _ blood-
corpuscles—for the first time; and in the course of his
description he interpolated an account of various “ animalcules ”
which he had discovered incidentally. Some of these animal-
cules were undoubtedly protozoa, but they are so involved
* Contemporary medical workers, however, were not slow to seize upon
the pathological possibilities of L.’s discoveries. For example we find,
as early as 1683, that “the ingenious Fred. Slare M.D. and ¥.R.8.”,
commenting upon a murren” in Switzerland which carried off many
cattle, says: ‘I wish Mr. Leewenhoeck had been present at the dissections
of these infected Animals, I am perswaded He would have discovered some
strange Insect or other in them.”—Slare [alias Slear] (1647 ?-1727) was
a physician and chemist. He qualified at Oxford in 1680, and became a
Fellow of the Royal Society in the same year—just after L. himself.
LETTER 88. 16 guLy 1683 931
with the other matters mentioned that it is not always easy to
separate them. The passages in question—omitting irrelevant
details (duly indicated)—are as follows:!
The first frog that I dissected sat in the road; and it
seemed so weak from the cold,’ that though I gave it a
bit of a kick on with my foot, it didn’t jump away. When
I picked it up and opened it, I found ’twas a female, in
whose guts there were worms, which had the shape of
those worms that children void in their stools.’ These
worms * were about as thick as a hair off one’s head.’
But what most surprised me was, that I observed in the
blood (which had run out of the many blood-vessels that
Thad cut, into the clean ° dish in which I dissected the frog)
a great number of living animalcules,’ which were about
" From Letter 38, 16 July 1683 [N.S.]. To Christopher Wren.
MS.Roy.Soc. Read at a meeting of the Society held on July 18 [0.S.] —
not on July 11, as appears (owing to omission of a date) in Birch, Vol. IV,
p. 215. Published in Brieven, Vol. I (Dutch) ; Opera Omnia, Vol. I (Latin).
The Dutch version first appeared in 1685 (Ontled. en Ontdekk.), and the
first Latin version in the same year (Anat. et Contempl.). In both of these
the letter is dated correctly : but in the Op. Omn. (and in the earlier Anat.
s. Int. Rer. [1687], which contains a 2nd edition of the Latin letter) it is
misdated July 26. A short English translation was published in Phil.
Trans. (1683), Vol. XIII, No. 152, p. 347; and this was therefore the first
version to appear in print. Hoole also translated a part of this letter, but
not that which here concerns us. My translation is based primarily upon
the original MS.
* In a previous (untranslated) paragraph it is noted that these frogs
were studied on 1 April 1683, when they were coupling. It is thus certain
that the species was Rana temporaria—not R. esculenta, which breeds later.
* Probably meaning Oxyuris (=Enterobius) vermicularis.
“The “worms” found in this frog were obviously not protozoa or
bacteria but nematodes; and— if the foregoing identification of Oxywris be
correct—they were probably Ozysoma brevicaudatum, which is very
common in R. temporaria.
° A description of the blood-corpuscles of the frog is here omitted.
° schone printed version. Not in MS.
" When all the particulars related are taken into account—size, host,
origin, movements, etc.—I think there can be very little doubt that this
‘animalcule”’ was Trichomonas (or Trichomastia ?) batrachorum.
y
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” al
”
s e
i* Ww
.
ce
232 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
half as long and half as broad as one of the oval blood-
corpuscles ; all being of one and the same structure.
‘Twas no small pleasure to see this sight: for I had let
so much time slip by, that the oval blood-corpuscles were
sunk down somewhat (owing to their weight) towards the
bottom, and then these animalcules made a pretty motion,
for as they went a-swimming, they knocked into the
blood-corpuscles, and sent them spinning. And I judged
that in every particle of blood as big as asand-grain there
were quite 50 animalcules.
The blood aforesaid was very watery, and not pure
blood by any means: for as soon as I separated a good
bit of the frog’s skin from the flesh, some watery juice‘
began to run out of the skin, as well as the flesh ; and still
more when I opened the belly. And as I had well-nigh
bashed in the frog’s head, trying to make it keep quiet,
methought some watery juice might well have been
squashed out of its mouth or stomach too, and from this
juice the animalcules might have come; for when I
afterwards took blood out of the frog’s veins clean, I
could discover no animalcules therein; neither when
I viewed the watery matter which came from between the
skin and the flesh, nor yet in that from the hollow of the
belly.’
In the foresaid watery matter, I noticed some irregular
particles, most of which looked to me round, and were about
as big as the globules of our blood. In some of these’ I
could make out that they were composed of 6 lesser
globules; and there were besides particles that seemed
only about 4 of the bigness of the others. And when I
* 4.¢., lymph.
* From the foregoing and succeeding passages it is clear that L. satisfied
himself that there were no animalcules in the blood or lymph: and
consequently there is no foundation for the statement—sometimes made—
that he discovered protozoa in the blood of the frog.
* Plasma-cells, from the lymph. The smaller “ globules” inside them
were doubtless the large basophile granules contained in such cells.
" wl y
dete Be
real
PAs
ie
PLATE XXIII
LEEUWENHOEK’S PICTURES OF THE INTESTINAL PROTOZOA OF FROGS
From the engravings in the Dutch edition of Letter 38 (16 July 1683). X 13.
Fig. A, Opalina (Cépédea) dimidiata.
Fig. B, Nyctotherus cordiformis.
Fig. C, a larval nematode ?
facing p. 233
PROTOZOA OF FROGS DISCOVERED 233
examined the said watery blood of divers frogs, that had
run out into the dish (for I took a clean dish for each
several frog), a very few animalcules were‘ to be seen in
it once more.
Because I couldn’t satisfy myself about the animalcules
aforesaid, though I was sure they didn’t belong to the
blood itself, but were gotten into it by accident; in the
month of June* I continued my observations, and at
last I came across some frogs* in whose dirt, which I
took out of the guts, I beheld an unconceivably great
company of living animalcules, and these of divers sorts
and sizes. ‘The biggest sort “ had the shape of Fig. A.2 Of
these I judged there were quite 40 in a quantity of
material as big as a grain of sand. ‘The second sort” had
the figure of B: these were very fewinnumber. The third
sort had very near the shape of our river-eels, as Fig. C:
these were in even greater plenty than the first. And
moreover the whole material was so full of little animal-
cules, that the very dirt seemed to consist of nothing but
little living animals; for the little particles of the dirt
itself were so stirred’ by the motions of the animalcules,
that they looked almost as though they were themselves
animalcules too.© The number of the little animalcules
* is MS.—corrected to zijn in printed version.
> Anno 1683.
* The species is not discoverable from this description, but the protozoa
found indicate that they were Rana esculenta—not R. temporaria. lL. knew
well (and could distinguish) both species. In Letter 65, 7 Sept. 1688, he
tells us that there are two kinds of frog (vorsch) in Holland—the common
“kikvorsch”’ [= R. temporaria], and the larger “ work” [= R. esculenta]
which is “ eaten by the French.”
* Opalina (Cépédea) dimidiata—without a doubt.
> hadden de fig: van. A MS. hadden de gedaante van Fig. 3. A. printed
version. See Plate XXIII.
° Nyctotherus cordiformis : but see below.
"wiert . . . bewogen MS.—corrected to wierden . . . bewogenin
print.
* This graphic description must appeal to every worker who has studied
the intestinal protozoa of frogs, for it vividly describes the usual appearance
234 LEEUWENHOEK AND HIS “LITTLE ANIMALS”’
last spoken of was so great, that I judged there were
several thousand of ’em in every bit of matter as big as a
sand-grain.
On seeing this, I took it for certain that the animalcules
which I said before were in the blood (which I had taken
out of the dish), came to be there only in this way:
namely, because the frog, when it was being cut up,
voided its dirt into the dish, or because I had unwittingly
wounded the guts of the frog, in whose dirt there must
have been many animalcules, which got mixed with the
blood.
It has been generally allowed that the larger animalcules
which Leeuwenhoek here described and figured (his Figs. A
and B) were ciliates—which occur so commonly in the guts
of frogs. But it is possible, I believe, to identify them more
exactly. To anybody familiar with the intestinal fauna of
the two common frogs of Northern Europe (Rana temporaria
and R. esculenta), it must be obvious that the abundant long
organisms (Hig. A) were Opalina (Cépédea) dimidiata, while
the smaller, scantier, and more rounded creature (Fig. B) was
Nyctotherus cordiformis. Both of these occur very commonly
in Lana esculenta, and I therefore infer that the frogs which
Leeuwenhoek was studying on this occasion were of this
species.”
It would have been impossible to determine the exact
species of these ciliates before the intestinal protozoa of frogs
had been adequately studied. Consequently, most of the early
identifications are not worth serious consideration. The first
correct determination we owe, I think, to Biitschli, who says
of frogs’ faeces under the microscope. The “animalcules’”’ responsible for
the phenomenon are flagellates (Trichomonas, Trichomastix, Chilomastiz,
and Hexamuta), and various motile bacteria.
" O. dimidiata is well known as the characteristic species of opalinid
from this host: Nyctotherws, however, is usually described as occurring in
i. temporaria only. That the above statement is correct I know from my
own observations.
* The frog in which L. found the worms previously was—as already
noted—f. temporaria: but there is nothing in his words to prove that the
frogs of the second batch were not of the other species. If they were, then
the above identification amounts almost to a certainty.
OPALINA AND NYCTOTHERUS Zao
that in Leeuwenhoek’s description “ Opalinae and Nyctotherus
can be recognized with sufficient certainty.”* No species are
indicated, though the two which I have mentioned must, I
think, have been intended. Saville Kent, however, had
previously identified Leeuwenhoek’s Fig. A as Opalina
intestinalis :” but this is highly improbable, because there is
no certain record of this species having ever been found in
either R. temporaria or R. esculenta.’
Metcalf, who has studied the Opalinidae in greater detail
than any other specialist, writes of Leeuwenhoek’s observations
as follows : *
‘“ Opalina was first mentioned [?] by Leeuwenhoek in
1685° [?]. In his Opera omnia (1722) he quotes the earlier
record [?] of finding innumerable animalculae [sic] of
various sizes and forms in the foeces [sic] of the frog. One
of these figured [L.’s Fig. B] seems in all probability to have
been O. ranarum. Another may have been O. dimidiata
DRG ya cates. diag
From this it seems to me that Metcalf cannot have studied
Leeuwenhoek’s works or words very carefully, nor does he
- appear to appreciate the difficulties of his own interpretation.
If—as he suggests, and as I am convinced—Fig. A represents
O. dimidiata, then the smaller rounded form (Fig. B) can
hardly have been O. ranarum. For this species is at least as
large as O. dimidiata, and occurs typically in a different host—
RR. temporaria.” Consequently, if Metcalf’s interpretation
were correct, it would leave the small size of Fig. B un-
' Biitschli (1887-89), Vol. III, p. 1101. The date of the observations is
wrongly given, however, as 1687. Cf. also zbzd., pp. 1718 and 1721.
* Kent (1881-82), Vol. II, p. 562.
* Opalina (Protoopalina) intestinalis is a species proper to Bombinator—
not Rana. Cf. Metcalf (1923), p. 51. Kent’s error was first noted by
Metcalf (1909), p. 319.
* Metcalf (1909), p. 319. My comments are interpolated in square
brackets for the sake of brevity. In my opinion this single sentence
contains at least six mistakes, but it seems unnecessary to do more than
indicate them.
° In a later work (Metcalf, 1923, p. 438) the date is given as 1865 [! ]—
presumably by misprint of the first date (1685), which was itself incorrect.
Little errors of this sort abound in nearly all discussions of L.’s work.
° I know of no certain record of O. ranarwm having been found in R.
esculenta, or of O. dimidiata from R. temporaria. Cf. also Metcalf (1923).
cc
236 LEEUWENHOEK AND HIs “ LITTLE ANIMALS”
explained, and would necessitate the assumption that
Leeuwenhoek found his ciliates not merely in two different
frogs, but in frogs of two different species—of which there is
no indication whatever in his own writings. But if, on the
other hand, it be agreed that Fig. A shows O. dimidiata, then
the frog was a specimen of R. esculenta, and the smaller ciliate
was Clearly Nyctotherus—not an opalinid at all. The figure
certainly suggests this strongly, and everything else supports
this obvious, natural, and easy interpretation.
When we come to consider Leeuwenhoek’s Fig. C, however,
we are faced with very grave difficulties. This organisin is
said to have been like a “‘ river-eel ”’, and to have been abundant
in the frog’s faeces: and in size it appears, from the figure, to
have been longer than a Nyctotherus—though the drawings
were not made accurately to scale. Elsewhere in Leeuwen-
hoek’s writings we find nematodes (Anguillula, etc.), spirilla,
and spirochaetes, all likened to “eels”: and in the rectal
contents of . esculenta we may find not only various species
of nematodes, spirilla, and spirochaetes, but also long flexible
and actively motile bacilli (Bacillus flexilis and similar forms).
To determine which—if any—of these Leeuwenhoek may have
seen on this occasion, is I think impossible. I must therefore
leave Fig. C unidentified, though I am inclined to believe that
it depicts a larval nematode.
I conclude, consequently, that Leeuwenhoek discovered
and described Opalina, Nyctotherus, and Trichomonas (or
Trichomastix) in the faeces of frogs, in addition to various other
protozoa and bacteria which are not now identifiable.’
And now we come to a letter which is, perhaps, as famous
as any Leeuwenhoek ever wrote to the Royal Society—the
one containing his account of the ‘‘ animalcules”’ in the human
mouth. This letter is frequently quoted—or rather mis-
" For example, there is a definite indication of the mouth, and the
outline is—to me—quite convincing. The interpretation of Fig. B as
Balantidium coli—recently put forward by Pritze (1928)—is so outrageous
as to deserve no further notice.
* I ought perhaps to point out that Prowazek (1913) has identified some
of these organisms with Balantidiwm coli. Although he has been copied by
others (e.g. Pritze, 1928), his interpretation is manifestly absurd. There is
no evidence that L. ever saw any species of Balantidiwm in the frog, and
B. colt certainly does not live in this host.
LETTER 88. CONCLUSIONS Ao tT|
quoted—by bacteriologists, and is usually said to be the first
memoir in which bacteria of any sort are mentioned. How
far this 1s true, readers of foregoing quotations can judge for
themselves. References to this important epistle, addressed
to Francis Aston, Sec.R.S.," are almost invariably given
incompletely or incorrectly ; and this is doubtless due in
part—though not altogether—to the fact that many versions
of it are extant. Moreover, many different interpretations of
the organisms described have been advanced, and this has led
to some truly astonishing conclusions. Yet Leeuwenhoek’s
words are, as usual, plain and straightforward, while the
interpretation of his observations appears to me obvious. To
anybody familiar with the flora and fauna of the human
mouth they surely present no difficulties. I shall therefore
give his own words (as well as I can) first, and shall comment
upon them afterwards—adding exact references but ignor-
ing many manifestly absurd statements made by other
commentators.
The passages in question run as follows: ?
* Concerning Francis Aston little is now known. (He is not mentioned
in the Dict. Nat. Biogr.) He was elected F.R.S. in 1678, and became
Secretary in 1681—a post which he suddenly threw up in 1685 (ef. Rec.
Roy. Soc., and Weld, I, 302). Afterwards he received a gratuity from the
Society (Weld, I, 305), and on his death bequeathed to them his estate at
Mablethorpe in Lincolnshire, together with his books and instruments
(Weld, I, 428). His portrait now hangs in the apartments of the Society
at Burlington House (at the foot of the staircase). For the following
additional information I am indebted to Mr H. W. Robinson, Assistant
Librarian of the Royal Society: Aston was born about 1644, and died in
June or July 1715. He went to Westminster School in 1656, and was
King’s Scholar in 1660 (aged 16). He entered Trinity College, Cambridge,
in 1661, and became Fellow in 1667. (B.A. Cant. 1664/5: M.A. 1668.)
He travelled abroad for some years, and in his youth was an intimate friend
of Isaac Newton.
* From Letter 39. 17 September 1683. To F. Aston. MS.Roy.Soc.
Published in Brieven, Vol. I (Dutch), and Opera Omnia, Vol. II (Latin).
The Dutch version was first printed in 1684 (Ondervind. en Beschouww.
pp. 1-19), the Latin in 1695 (Arc. Nat. Det. pp. 41-53). Both versions are
wrongly dated the 72th of the month (‘‘ den 12 Septemb. 1683” and “ pridie
Iduum Septembris 1683”) apparently through a misreading of the MS.
Owing, it would seem, to some oversight, two different English abstracts
appeared in the Plil. Trans. The first was published in Vol. XIV (1684),
No. 159, p. 568 [b¢s—a misprint for 598]: the second in Vol. XVII (1693),
No. 197, p. 646. [The first—published 20 May 1684—is the fuller and
better.] Hoole (1798) has given a third—and as far as it goes the best—
938 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
I have ere this sent you my observations concerning
spittle, which I see have been made public in print in the
Lectures and Collections published by Mr. Robert Hooke,
Secretary of the Roy. Soc., in the year 1678.’ Since
that time I have made divers further observations on
my spittle, with the idea that if there be any animalcules
lying about in the body, they would get into the mouth,
sooner or later, through the spit-ducts; but in what
observations I made to this end, I could make out no
animalcules there, nor could I say aught else but what
I have hitherto writ.
"Tis my wont of a morning to rub my teeth with salt,
and then swill my mouth out with water: and often,
after eating, to clean my back teeth with a toothpick, as
well as rubbing them hard with a cloth: wherefore my
teeth, back and front, remain as clean and white as falleth
to the lot of few men* of my years,’ and my gums (no
partial English translation in Select Works, Vol. I, p. 118. Léffler (1887,
p. 5) has translated a fragment into German, but he misdates the letter
September 14. It was read at a meeting of the Society held on 24 October
1683 [O.S.]: ef. Birch, Vol. IV, p. 219. Various reproductions of the
illustrative figures are noted below (p. 244 et seq.). They have already
given rise to much confusion and misstatement.—-Though there are already
at least one Dutch, two Latin, and three English versions of this letter in
print, I rely upon the original MS. (in L.’s own hand), from which my
translation has been made.
"A reference to Letter 23, 14 January 1678. To R. Hooke.
MS.Roy.Soc. English version (incomplete) published in Hooke’s Lect. &
Collect. (1678), part II, Letter 2, p. 84. (Reprinted in Hooke’s Lect. Cutl.
(1679) pt. V.)—This letter contains an account of certain ‘‘ Globules in the
Flegm’’: but L. had examined saliva still earlier, for in Letter 4 (1 June
1674, to Oldenburg) he notes that ‘‘In clean spit, examined by me in the
morning, I find a few very little particles floating in the liquid; whereof
I saw some sink to the bottom; as also divers irregular particles, some of
which seemed to consist of globules stuck together. And in the spittle that
I examined in the afternoon, I found the globules and irregular particles in
greater plenty”. (MS.Roy.Soc. Partial English translation in Phil. Trans.
(1674), Vol. IX, No. 106, p. 121.)
* als er weijnig menschen van mijn Jaren sign MS. als weynig
menschen . . . gebeurt printed version.
* When he wrote this, L. was approaching his 51st birthday. He tells
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PLATE XXIV
LEEUWENHOEK’S FIGURES OF BACTERIA FROM THE HUMAN MOUTH
(Letter 39, 17 Sept. 1683)
Enlarged (X 13) from the engravings published in Arc. Nat. Det., 1695.
Fig. A, a motile Bacillus.
Fig. B, Selenomonas sputigena. C....D, the path of its motion.
Fig. E, Micrococci.
Fig. F, Leptothrix buccalis.
Fig. G, A spirocheete—probably “ Spirochaeta buccalis,” the largest form found
in this situation.
facing p. 239
LETTER 39. 17 SEPTEMBER 1683 939
matter how hard the salt be that I rub them with) never
start bleeding. Yet notwithstanding, my teeth are not
so cleaned thereby, but what there sticketh or groweth
between some of my front ones and my grinders (whenever
I inspected them with a magnifying mirror), a little
white matter, which is as thick as if ’twere batter.” On
examining this, I judged (albeit I could discern nought
a-moving in it) that there yet were living animalcules
therein. I have therefore mixed it, at divers times, with
clean rain-water (in which there were no animalcules),
and also with spittle, that I took out of my mouth, after
ridding it of air-bubbles (lest the bubbles should make
any motion in the spittle): and I then most always saw,
with great wonder, that in the said matter there were
many very little living* animalcules, very prettily
a-moving. The biggest sort had the shape of Fig. A*
[Plate XXIV]: these had a very strong and swift
motion, and shot through the water (or spittle) like a
pike * does through the water. ‘These were most always
few in number.
The second sort had the shape of Fig. B. These oft-
times spun round like a top, and every now and then
took a course like that shown between C and D: and
these were far more in number.
us elsewhere, however, that he sometimes suffered from toothache—to
alleviate which he smoked a pipe of tobacco, which generally made him
feel very sick. He also tells us later how some of his teeth decayed.
‘ Nogtans printed version—omitted in MS.
* beslagen meel MS. and Dutch printed version “wetted flower” Phil.
Trans. (1684) “like a mixture of flour and water” Hoole farinae aqua
subactae similem Latin edition. The 2nd Phil. Trans. version (1693)
incorrectly calls this soft mealy material (materia alba) ‘‘a kind of gritty
Matter.”
* levende is here in the MS. but not in the printed version.
* hadde de Fig: van A. MS. was van de Fig: A. printed version.
® een snoek MS. and Dutch printed version. The Latin translator
rendered this—with some justification—piscis lupus: which caused Loffler
(1887, p. 5) to mistranslate it ‘‘ Rauwbfisch” (instead of Hecht). To “ shoot
through the water like a pike” is a phrase commonly used by L. to describe
any rapidly darting aquatic animalcule.
240
1
2
3
Lat.
LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
To the third sort I could assign no figure: for at times
they seemed to be oblong, while anon they looked
perfectly * round. ‘These were so small that I could see
them no bigger than Fig. HK: yet therewithal they went
ahead so nimbly, and hovered so together, that you might
imagine them to be a big swarm of gnats or flies, flying in
and out among one another. ‘These last seemed to me
e’en as if there were, in my judgement, several thousand
of ’em in an amount of water or spittle (mixed with the
matter aforesaid) no bigger than a sand-grain; albeit
there were” quite nine parts of water, or spittle, to one
part of the matter that I took from betwixt my front
teeth, or my grinders.
Furthermore, the most part of this matter consisted of
a huge number of little streaks, some greatly differing
from others in their length, but of one and the same thick-
ness withal; one being bent crooked, another straight,
like Fig. F, and which lay disorderly ravelled together.
And because I had formerly seen, in water, live animal-
cules that had the same figure, I did make every
endeavour to see if there was any life in them; but
I could make out not the least motion, that looked lke
anything alive, in any of ’em.
I have also taken spittle from the mouths of two
different womenfolk,’ that I’m sure clean their teeth
every day, and examined it as narrowly as I was able to,
but could discern therein no living animalcules. But
afterwards I examined the same spittle mingled with
a little of the matter that I picked out with a needle from
betwixt their teeth : and then I discovered as many living
volkomen is here in the printed text, but not in the manuscript.
was MS.—corrected to waren in print.
twee distincte Vrouwspersonen MS. and Dutch ed. binaruwm foeminarum
5 ce ?
ed. ‘‘two several women” Phil. Trans. (1684) other Persons ”’
Phil. Trans. (1693) “‘ two ladies’ Hoole (1798). It is almost certain that
these were L.’s own womenfolk—his second wife Cornelia, and his daughter
Maria.
PLATE XXV
Cle odo eve Len Soe bch WI & he oars on gel , Lu
Sohoefen gree hi rterater po fission ocses
AD Chex fo DEN TS
feos Sot Oe why an a WEA
Ee je re meh C. em D. tf atm poweden \' Soke learner
Creel am cerder amt geht. Jhon de: (eDe Srost- Poul Mat
~~, Seo clin LOB spew) eno De ander
4 ne A ‘a - ele Date! binerce Soe Ze. oat
eh eleles & age cee LeQe devi eee ha E. mat
ew eer. Cae he far So
ea, cr a Astin’ "Nets nna shp
.
hwel te Gerren men { dat-iL cordece cen
Soi ER te ry ae
(Oem x amet Ve ie 5% of peed
Rae Asem Shevere
ettte rmatene Ky etn over
ae ye abe. (GEL (ee ies. Klidentre Cle phi ouwe +5 aD
4, ogtang Comm Lon ade Deh. =: ibe Scull
Vie tier te mete Bk cpt Py Fs ange,
ro es SMES SP ie we ao
wwe Dea oak ee ington Tae Laven Seb leo
aii 4! Aaildesin se Ae heb 1k, atte (Qeserreny : oon Blond — pO
"£3 S Bic ph de ae VWogex m cai On aor ik heb 9 eeu
)
Peuwregr, aft rie gf there: gelek , ja ay~
ys Anan 4 < an J f ‘2 sy o d nti
A PAGE OF THE ene tie HOLOGRAPH MS. OF LETTER 39
(17 Sept. 1683: leaf 2 recto = page 8),
containing part of Leeuwenhoek’s description of the Bacteria in the mouth.
Facsimile. (The first word is [desel] ve, continued from the previous page.)
This is a good sample of Leeuwenhoek’s handwriting at this period.
facing p. 240
ee CA rey aU Pep me MUN ee emt es et ee
“oy eiy : ih NI. 3 aie va ne ay OL Pa iy bik
ay ve halt Bs Wb eee See “3 kk 4 Py Tue J) Md " rr ~
op ee aad ne
% tee, caNT eo
; a i he ; hid Bh . i tor ae a oy re : we - o i
Farben me ii me! ata: GIN apt!
Ccemauenen ett par pers
ae Ce ae me mag
yey i
ae . re tan 7 ee
a Le te, 5 date}
A} rca! weer; agit) See a 2: =e 5 tf \ Atel rie
sie a eh Pith ene + es
‘ he | wee
77° Sey
"a
o seca) Sie As
tant 7 \ P), oy Hye Em
. 7 ’
aA Wiki te c g }
7 i be | i
t vans ask
it: ey - ‘aye a i
h 4 8 is
eo 14
ee eee
Poe ie presge af
an te i 2 ru a yeu!
: - wi f
ae Ht » i, ~* aie ; , ; : ~ a
al hoe el i ona
7 ee 77 h
ae ee
7 ager be
Disa ie} iikennk 1h
| any ah a _ yids: ah
a % ‘ ans Aas i waka
ke ~~ va ie
oa An oN oN
ton - ie
‘
i ea i
i. yor ile
ay haere i
BACTERIA IN THE HUMAN MOUTH 241
animalcules, together with the long particles, as herein-
before related.
I have also examined the spittle of a child about eight
years old, and likewise could discover no living animalcules
therein ; and afterwards the same spittle, mixed with the
stuff that I got out from atween the child’s teeth: where-
upon I perceived as great a many animalcules and other
particles as heretofore made mention of.
I didn’t clean my teeth (on purpose) for three days
running, and then took the stuff that had lodged in very
small quantity on the gums above my front teeth; and I
mixt it both with spit and with fair rain-water;* and
I found a few living animalcules in it too.
While I was talking to an old man (who leads a sober
life, and never drinks brandy or tobacco,’ and very seldom
any wine), my eye fell upon his teeth, which were
all coated over; so I asked him when he had last cleaned
his mouth? And IJ got for answer that he’d never washed
his mouth in all his life.” So I took some spittle out of
his mouth and examined it; but I could find in it nought
but what I had found in my own and other people’s. I
also took some of the matter that was lodged between and
against his teeth, and mixing it with his own spit, and also
with fair water (in which there were no animalcules), I
found an unbelievably great company of living animalcules,
a-swimming more nimbly than any I had ever seen up to
this time. The biggest sort (whereof there were a great
plenty) bent their body into curves in going forwards, as
in Fig. G. Moreover, the other animalcules were in such
enormous numbers, that all the water (notwithstanding
' water MS. vregen-water Dutch printed version.
2 In olden times it was customary to speak of “ drinking” tobacco—
)
both in Holland and in England—though it meant “ smoking ” (as we now
* Hoole (1798, p. 119)—with his usual squeamishness—purifies these
coarse details into more polite observations upon “ the teeth of an old
gentleman, who was very careless about keeping them clean.
16
242
cc
LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
only a very little of the matter taken from between the
teeth was mingled with it) seemed to be alive. The long
particles too, as before described, were also in great
plenty.
I have also taken the spittle, and the white matter that
was lodged upon and betwixt the teeth, from an old man’
who makes a practice of drinking brandy every morning,
and wine and tobacco in the afternoon; wondering
whether the animalcules, with such continual boozing,
could e’en remain alive. I judged that this man, because
his teeth were so uncommon foul,’ never washed his
mouth. So I asked him, and got for answer: ‘‘ Never
in my life with water, but it gets a good swill with wine
or brandy every day.” Yet I couldn’t find anything
beyond the ordinary in his spittle. I also mixed his spit
with the stuff that coated his front teeth, but could make
out nothing in it save very few of the least sort of living
animalcules hereinbefore described time and again. But
in the stuff I had hauled out from between his front teeth
(for the old chap hadn’t a back tooth in his head), I made
out many more little animalcules, comprising two of the
littlest sort.
Furthermore, I put some strong wine-vinegar in my
own mouth, and then set my teeth, and let the vinegar run
betwixt ’em time after time: and after doing so, I rinsed
my mouth out thrice with fair water. Afterwards I once
more fetched out some of the foresaid stuff from between
my front teeth, as well as from between my grinders ;
and I mixed it divers times both with spittle and with
clean rain-water: and most always I discovered in it
an unbelievable number of living animalcules, though most
of ’em were in the matter I got from between my back
teeth, and only a few had the appearance of Fig. A.
1
Hoole (1798) prudishly refrained from translating the observations
made upon this disreputable ‘old gentleman”’, who, in the Phil. Trans.
(1684), is called simply—without other descriptive detail—" a good fellow ”.
”
2 ongemeen vurjl MS. buyten gemeen vuyl printed letter.
1
BACTERIA IN THE HUMAN MOUTH 243
I have also put a little wine-vinegar to this stuff mixed
with spittle, or with water: whereupon the animalcules
fell dead forthwith. And from this I drew the conclusion
that the vinegar, when I filled my mouth with it, didn’t
penetrate through all the matter that is firmly lodged
between the front teeth, or the grinders, and killed only
those animalcules that were in the outermost parts of
the white matter.
In several of the observations aforesaid, I saw on 2 or
3 occasions some very bright transparent particles,
whereof many were perfectly round, others having an
irregular round figure. ‘These were of divers bignesses,
and the biggest of them I judged to be about 25 times
bigger than a globule of one’s blood’: and if they hadn’t
sunk to the bottom, by reason of their weight, I should
have taken them for fat-particles.’
I have had several gentlewomen in my house, who
were keen on seeing the little eels in vinegar: but some
of ’em were so disgusted at the spectacle, that they vowed
they’d ne’er use vinegar again. But what if one should
tell such people in future that there are more animals
living in the scum on the teeth in a man’s mouth, than
there are men in a whole kingdom ? especially in those
who don’t ever clean their teeth, whereby such a stench
comes from the mouth of many of ’em, that you can
scarce bear to talk to them; which is called by many
people “ having a stinking breath”, though in sooth ’tis
most always a stinking mouth. For my part I judge, from
myself (howbeit I clean my mouth like I’ve already said),
that all the people living in our United Netherlands are
not as many as the living animals that I carry in my
own mouth this very day: for I noticed one of my back
teeth, up against the gum, was coated with the said matter
z.e., they had about thrice the diameter of a human red blood-corpuscle.
These were probably squamous cells—the smaller being “salivary
corpuscles ” (dead leucocytes).
2
vet-deeltgens ; 2.e., oil droplets.
244 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
for about the width of a horse-hair, where, to all appear-
ance, it had not been scoured by the salt for a few days ; *
and there were such an enormous number of living
animalcules here, that I imagined I could see a good 1000
of ’em in a quantity of this material that was no bigger
than a hundredth part of a sand-grain.’
It must be noted here that the illustrations accompanying
the foregoing letter differ slightly in each version. The
original drawings are, unfortunately, lost: and the_ best
figures—those now reproduced—are in the original Latin
edition (Arc. Nat. Det., 1695) and Opera Omnia. From the
first Dutch edition® (1684) Fig. G, a highly important
picture, was for some unexplained reason omitted altogether."
In the first Phil. Trans. version (1684) all the figures appear,
but Fig. G has an irregular and unrecognizable shape: while
in the second Phil. Trans. version (1693) Fig. G again
disappears, and the others are reversed.’
A plausible explanation of these discrepancies is the
following. The figures originally sent by Leeuwenhoek to the
Royal Society were badly drawn and poorly engraved, and he
was probably dissatisfied with them—especially with Fig. G,
which was very bad. When he was about to publish the
same pictures himself later in the same year, he resolved to
have this figure redrawn, and therefore told the engraver not
to copy the original. Then, by an oversight, the letter was
printed with the figure missing. later, discovering his
mistake, Leeuwenhoek had a new and improved drawing
’ The Latin version inserts here ‘‘ materiam illam inde exemi’’ [=so I
extracted some of this stuff], but this is not in the Dutch originals.
2 The sentences in the foregoing paragraph are loosely strung together
and ungrammatical in the original: and consequently they are not easy to
translate into intelligible English without “ improving ’’ beyond recognition.
If the reader should find my version inelegant and confused, I would refer
him to its prototype—which is much worse.
® In the only copy of the 2nd Dutch edition of L.’s works which I have
yet seen, the whole letter containing these observations (No. 39) is
missing—the copy being otherwise perfect.
* It is referred to, however, in the text (both MS. and printed Dutch
version).
’ This is obviously due to the engraver’s direct copying of the original
drawings on to his plate.
LETTER 39. INTERPRETATIONS 945
prepared, and this was inserted in the Latin translation which
appeared subsequently. The still later omission of Fig. G
from the second Phil. Trans. version was probably merely a
consequence of the great condensation which this very short
and faulty translation underwent at the hands of its editors.
Some such explanation would readily account for the
variations in the different versions. But in any case, I think,
we need not hesitate to accept the final and complete set of
drawings published with the Latin letter—drawings which
Leeuwenhoek must himself have seen and passed for press.
The omission of Fig. G from the Dutch edition was certainly
unintentional, as it is referred to in the letterpress.
It is not possible to doubt, after reading the foregoing
descriptions and inspecting the pictures, that Leeuwenhoek
discovered ‘the bacteria in the human mouth: for he described
—and described recognizably—all the most characteristic
forms occurring in this situation. To anybody familiar with
these organisms his figures speak so clearly that his words are
almost superfluous. If I were shown these sketches for the
first time, and asked to interpret them, I should be able to
say—after only a moment’s reflexion—what they probably
depict. Fig. A is a Bacillus: Fig. B shows the peculiar
organism known as “ Spirillum sputigenum” :° Fig. EK shows
some of the Micrococct commonly present in the mouth: Fig.
"IT must note that priority for this discovery has been claimed for
Hartsoeker: but this is due to a misunderstanding. The true story can
be pieced together from L.’s writings and Hartsoeker’s own words (1730).
Hartsoeker, knowing of L.’s discovery of the spermatozoa, tried to pass it
off as his own: but he says that he was ashamed to tell people that he had
examined semen with the microscope, and therefore told them at first that
the “ animalcules’’ which he had found in it were in the saliva. But he
further says, quite definitely (1730, p. 6), that he never really saw any
animalcules in saliva, and he attempts to discredit L.’s discovery. He
regarded it as an invention. Consequently, Hartsoeker himself never
claimed to have found any organisms in the human mouth, and even
denied their existence.
2 So named by Miller (1890). This organism is not really a Spirillwm
at all, but belongs to the genus Selenomonas Prowazek, 1913a. I have
studied it (in pure culture) but I have seen no accurate description of it.—
In the genus Selenomonas the flagella arise from the concave surface of the
arched or crescentic body—not from its ends, as in Spirillum. Their
lashing produces the curious whirling motion observed by L. Although the
text-books of bacteriology are usually silent on the subject, I can say from
my own knowledge that Selenomonas sputigena is very common in human
mouths—and very difficult to isolate in cultures.
946 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
F is the Leptothriz’* always found on the human teeth: and
Fig. G is unquestionably a spirochaete—probably the so-called
“ Spirochaeta buccalis”.” The figures obviously represent
bacteria, and include no protozoa; and nowhere but in the
mouth is such an assemblage of forms to be found. When
Leeuwenhoek’s own words are considered in conjunction with
these illustrations, the interpretations just advanced must
surely be self-evident to everybody who studies the microbes
of the human mouth “ with the help of a good microscope.”
Yet ever since the foregoing observations were recorded
they have been misinterpreted—and even questioned and
denied—in the most astonishing manner. It is unnecessary
to chronicle here all the wild assertions that have been made
in this connexion.’ 'T'wo of the most recent comments will
serve as illustration :
(i) Singer (1914) reproduces the figures from the Phil.
Trans. 1684 (misdated by him 1683), and says that figs. A, F,
and G [the spirochaete] are all ‘‘rod-shaped organisms ”’
[meaning bacilli?]; and that B [Selenomonas| is “a flagellated
organism” [meaning a protozoon?]|. He even recognizes
‘ sarcinae’”’ in Leeuwenhoek’s description: but the figure * so
strangely interpreted is said by Leeuwenhoek himself to
represent epidermal scales from the human skin, as seen
under a low magnification.
(ii) Wenyon (1926), discussing the Trichomonas of the
human mouth, says “it is probable that Leeuwenhoek saw
the flagellate in the tartar of his own and other people’s
teeth.”°’ Although no reference is given to the passage in
' Leptothrix buccalis Robin, 1853: Bacillus maximus buccalis Miller,
1890.
| 7 specific designation commonly ascribed to Cohn. But see Dobell
1912).
* I must mention, however, that Robin (1853, pp. 352-354) made a
careful study of the Latin versions of Letter 39, and correctly identified the
Leptothrix. Ue also recognized Fig. B as a “vibrion”’. Beijerinck (1913,
p. 10, note) wrongly supposes that Ldéffler (1887) was the first to direct
attention to L.’s pictures of bacteria in the human mouth.
* Fig. H—which occurs in the same letter, but is not reproduced here.
To my mind this figure bears no resemblance to a Sarcina or any other
bacterium : and of course no Sarcina lives normally in the mouth of man.
° Wenyon (1926), Vol. I, p. 656. So far as I am aware, there is no
passage in any of L.’s writings which can be plausibly interpreted as an
account of the Trichomonas of the human mouth.
NOTES ON LETTER 389. LETTER 75 Q47
which T'richomonas is supposed to have been described, it is
clear that Wenyon must here refer to one or other of the
“animalcules’’ which we have just discussed—but which
one, I cannot even guess. To me it is obvious that they were
all bacteria: but Wenyon takes the view that none of them
could have been, since he considers that bacteria ‘“‘ were quite
beyond the scope of the simple magnifying apparatus used by
Leeuwenhoek.” ?
Thus, while Singer finds, in Leeuwenhoek’s words and
pictures, more bacteria than Leeuwenhoek himself, Wenyon is
able to recognize none at all!
Some further researches on the ‘“animalcules” in the
human mouth were reported by Leeuwenhoek nine years
later. His letter runs as follows: ?
In my letter of the 12th* of September, 1683, I spake,
among other things, of the living creatures that are in
the white matter which lieth, or groweth, betwixt or
upon one’s front teeth or one’s grinders. Since that
time, and especially in the last two or three years, I have
examined this stuff divers times; but to my surprise, I
could discern no living creatures in it.
1 Wenyon (1926), p. 3.
2 From Letter 75. 16 September 1692. To the Royal Society.
MS.Roy.Soc. Printed in full in Brieven, Vol. II, p. 508: Opera Omnia,
Vol. II, p. 307 (1st pagination). The Dutch version first appeared in 1693
(Derde Vervolg d. Brieven), the Latin in 1695 (Arc. Nat. Det., p. 334). No
English translation was ever published in the Phil. Trans., and so far as I
am aware no English version has yet appeared in print. (Hoole did not
translate the relevant passages in this letter.) A German paraphrase—of a
fragment only—is given by Léftler (1887, p. 6), who misdates the epistle
October 1.—The printed Dutch version follows the original MS. so closely
that few annotations are necessary : while the Latin version in Opera Omnia
(ed. noviss., 1722)—by an unknown hand—is one of the best translations I
have ever read. Barring a few trivial misprints, it renders its Dutch
prototype with wonderful faithfulness.—The originals of the illustrations
are lost ; the MS. in the Roy.Soc. collection being accompanied by a proof
of the engraved plate sent by L. himself in place of the original sketches.
* As noted already (p. 237, note 2), the correct date of this letter—
as written by L. himself on the MS.—is not the 12th but the 17th of
September.
248
LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
Being unable to satisfy myself about this, I made up
my mind to put my back into the job, and to look into
the question as carefully as I could. But because I keep
my teeth uncommon clean, rubbing them with salt every
morning, and after meals generally picking them with a
fowl’s quill, or pen; I therefore found very little of the said
stuff stuck on the outside of my front teeth: and in what
I got out from between them, I could find nothing with
life in it. Thereupon I took a little of the stuff that was
on my frontmost grinders; but though I had two or
three shots at these observations, ’twas not till the third
attempt that I saw one or two live animalcules. Yet I
could well make out some particles lying about that I
felt sure must have been animalcules. This put me in a
quandary again, seeing that at and about the time when
I wrote to you concerning these animalcules, I never
failed to see there was life in them: but though now I
used just the very same magnifying-glass and apparatus
(which I judged to be that best suited to the purpose),
yet I couldn’t make out any living creatures at all.
Having allowed my speculations to run on this subject
for some time, methinks I have now got to the bottom
of the dying-off of these animalcules. The reason is, I
mostly or pretty near always of a morning drink coffee,
as hot as I can, so hot that it puts me into a sweat:
beyond this I seldom drink anything save at mealtimes
in the middle of the day and in the evening; and by
doing so, I find myself in the best of health. Now the
animalcules that are in the white matter on the front-
teeth, and on the foremost of the back-teeth, being unable
to bear the hotness of the coffee, are thereby killed: like
I’ve often shown that the animalcules which are in water
are made to die by a slight heating.
Accordingly, I took (with the help of a magnifying
mirror) the stuff from off and from between the teeth
further back in my mouth, where the heat of the coffee
couldn’t get at it. This stuff I mixt with a little spit
out of my mouth (in which there were no air-bubbles),
LETTER 75. 16 SEPTEMBER 1692 249
and I did all this in the way I’ve always done: and then
I saw, with as great a wonderment as ever before, an
unconceivably great number of little animalcules, and
in so unbelievably small a quantity of the foresaid stuff,
that those who didn’t see it with their own eyes could
scarce credit it. These animalcules, or most all of them,
moved so nimbly among one another, that the whole stuff
seemed alive and a-moving.
I again paid the strictest attention I possibly could to
the bigness, or at any rate to the length, of the bodies of
many of ’em'; but mostly to the little animalcules, which
looked to me roundish. Afterwards, I took a grain of
coarse sand (of the sort of sand that we use here in this
country* for scouring the pewter, and other household
chattels), and I stuck this sand-grain in front of the
microscope through which I had seen the animalcules :
and I am bound to say, after making careful measure-
ments, which I did by eye, that the diameter of the sand-
grain was above a thousand times longer than the diameter
of one of the little animalcules which I saw in great
numbers. Consequently, then, such a grain of sand was
far more than a thousand millionfold bigger than one of
the little creatures aforesaid.
Besides, I also saw divers animalcules * whose bodies
were a bit thicker than the little animals hereinbefore
spoken of; but these were quite 5 or 6 times longer than
they were thick, and therewithal their body was of equal
thickness all along, so that I couldn’t make out which
was their head, or which their tail end; all the more
because when they were a-swimming, which they did
very leisurely (and this was their only motion, with a
little bending of the body now and then, as it seemed to
me), they would go ahead first with one end of the body
a
1 de hoe grootheijt of de lengte van veele haar lighamen MS. . . . of
wel de lengte van veele haar ’er lighamen Dutch printed version.
2 alwaar hier te lande MS. waar mede hier te lande printed version.
* Obviously bacilli of some sort, but otherwise unidentifiable.
250
LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
in front, and anon with the other.t’ These animalcules,
as they appeared to me, I have shown in Fig. A. [See
Text-fig. 4.]
And I saw, too, sundry animalcules”’ that had very
near the same length, and also some a bit longer. These
moved their bodies in great bends, in comparison of the
first animalcules, and made with their bendings so swift
a motion, in swimming first forwards and then backwards,
and particularly with rolling round on their long axis,
that I couldn’t but behold them again with great wonder
i as 3 B
ee ig
\ ~—
=a —
Sis Cc fy.
———" Se
a a
[Text-Fia. 4]
and delight: the more so because I hadn't been able to
find them for several years, as I’ve already said. For I
saw not alone the nimble motion of their own body; but
the little animalcules too, which swam in great plenty
round about these animalcules, were shoved off or driven
away from them, just as if you imagined you saw a
butterfly or moth flitting among a swarm of gnats, so
that the gnats were all wafted away by the butterfly’s
wings. ‘These animalcules I have represented in Fig. B.
1 This very acute observation was made on other bacteria, of course, at
a much earlier date—as already noted. It furnishes conclusive proof that
the organisms observed were bacteria.
2 From the following account these were evidently spirochaetes again:
but the figures are very poor, and could hardly be identified without L.’s
description of the organisms themselves.
BUCCAL BACTERIA REDESCRIBED 251
Furthermore, I saw animalcules* that were of very
near the same thickness, but of singular length. These
had so little” motion that I had most times to confess
they might not be living creatures at all; yet when I
could keep my eye on them, without getting tired, I
could make out that they bent their body very slow, just
bending it into a very faint curve, so that they didn’t
move forward, or very little. ‘These animalcules, as they
looked to me, are shown in Fig. C.
Now I also saw yet other animalcules,* that were of
very nigh the same thickness, but which in length even
surpassed those last described. But you seldom saw two
of this sort alongside, or floating off in the wet stuff, that
were of one and the same length. ‘These animalcules * too
were ’ in great numbers, whereof some were straight, while
others had a kink in them, as shown in Fig. D. But
the longer these animals were, the less motion or lfe
could I discern in them: and notwithstanding I could
make out no life in ’em, yet I made sure they were living
creatures, or had been such when they were in the mouth,
and situated on the back teeth, where many are
generated.
But we must be still more amazed when we consider
how these animalcules can move, and shift ’emselves
about, in stuff as thick as this is when it is lodged upon
and betwixt the teeth; and how hard and slow it must
be for them to get about in such stuff. But when, on
the other hand, the said stuff is mixed up with spittle,
and by this mixing the animalcules find themselves in a
fluid material, many of them feel released, as it were, and
never stop moving, so far as the eye can see.
-
? Leptothria.
seer weignig MS. soo weynig printed version.
N
* Leptothrix—almost certainly.
* Dierkens MS. omitted from printed letter.
sijn MS. and printed version: apparently a mistake for waren. The
Latin version has erant, and I make the same correction.
oa
252 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
It must be confessed that the foregoing observations add
little to those made previously. But bacilli, spirochaetes, and
Leptothrix are again recognizably described—if not recogniz-
ably figured: and this letter therefore confirms, to some
extent, the earlier one (No. 39). It also gives us a characteristic
glimpse of the author and his methods, and for that reason—
if for no other—deserves notice.
Various writers have already reproduced the illustrations
accompanying this letter, but nobody hitherto appears to have
made any attempt to interpret them—apart from noting that
they represent “ bacteria”. This is to be explained, I think,
in the usual way : most people merely glance at Leeuwenhoek’s
figures and do not take the trouble to read his words relating
to them, so that his excellent observations have been all too
often misunderstood or treated as mere curiosities.’
A few further observations on the bacteria about the teeth
were interpolated in a letter written to the Royal Society
five years later. In the midst of a discussion of the eggs of
snails, the germination of wheat, and the spat of oysters, we
find the following digression :”
I can't forbear to tell you also,’ most noble Sirs, that
one of the back teeth in my mouth got loose again, and
bothered me much in eating: so I decided to press it
hard on the side with my thumb, with the idea of making
the roots start out of the gum, so as to get rid of the
Tn passing, I may also add that a recent writer (Prescott, 1930) cites
the foregoing letter (No. 75) as evidence that “ A. von Leeuwenhoek ”’ held
the view “that microscopic organisms were produced spontaneously from
non-living matter.” It is difficult to conceive how anybody who has ever
read a word of L.’s writings could make such a mistake: but perhaps
Prescott—like many another writer who quotes L.—did not consult the
work to which he refers. This would also explain the singular fact that he
cites the original Latin edition of the letter (1695) but gives the pagination
of the editio novissima (1722).
2 From Letter 110. 10 September 1697. To the Royal Society.
MS.Roy.Soc. Printed in Brieven, Vol. III (Sevende Vervolg, 1702); Opera
Omnia, Vol. III (Epist. Soc. Reg., 1719); and in abbreviated English in
Phil. Trans. (1697), Vol. XIX, No. 235, p. 790. The passage here
translated begins on p.40 of the Dutch edition, p.35 of the Latin, and
p. 797 of the Phil. Trans.
° ook printed version: not in MS.
LETTER 110. 10 SEPTEMBER 1697 253
tooth ; which I succeeded in doing, for the tooth was
left hanging to only a small bit of flesh, and I was able
to snip it off very easily.
The crown of this tooth was nearly all decayed, while
its roots consisted of two branches ; so that the very roots
were uncommon hollow,’ and the holes in them were
stuffed with a soft matter.
I took this stuff out of the hollows in the roots, and
mixed it with clean rain-water, and set it before the
magnifying-glass so as to see if there were as many living
creatures in it as I had aforetime discovered in such
material: and I must confess that the whole stuff seemed
to me to be alive. But notwithstanding the number of
these animalcules was so extraordinarily great (though
they were so little withal, that ’twould take a thousand
million of some of ’em to make up the bulk of a coarse
sand-grain, and though several thousands were a-swim-
ming in a quantity of water that was no bigger than a
coarse sand-grain is), yet their number appeared even
greater than it really was: because the animalcules, with
their strong swimming through the water, put many little
particles which had no life in them into a like motion,
so that many people might well have taken these particles
for living creatures too.
These were Leeuwenhoek’s last recorded observations on
the bacteria of the mouth, but there is another reference to
bacteria which he saw in a decoction of the “fur” off his own
tongue some years later. Although these were obviously
putrefactive organisms, and not species proper to the human
1 The original words are 200 dat selfs de Wortels boven gemeen hol waren.
The Latin translator apparently took this to mean that the wpper parts of
the roots were hollowed out (as is very probable, of course), for he renders
these words “ superior wtriusque radicis pars admodum erat excavata”’: but
boven gemeen is a common expression with L., and always means
“unusually” or “out of the common run of experience.” In the Phil.
Trans. the words “boven gemeen hol” are absurdly mistranslated
“extraordinary whole ”’
2 de groote van een grof zand printed letter . . . geen grof zand MS.
254 LEEUWENHOEK AND HIS “LITTLE ANIMALS ”’
mouth, I shall quote his words here—as they are not wholly
irrelevant in the present context. In an interesting letter
written in June, 1708, he said:?
At the latter end of the month of April, 1708, I was
again seized with a high fever, which stayed with me for
four days, rising higher each night; and as my tongue
was again coated with a thick whitish matter, I oft-times
removed some of it, which seemed stuck very tight
to the parts of the tongue, with a small penknife or with a
silver tongue-scraper: and viewing it many times through
the magnifying-glass, I could see nought else but what I
have described * in my previous dicconenee
On two occasions, I took some of the foresaid stuf from
my tongue, and put it in a small clean China coffee-cup,’
and then poured boiling rain-water upon it, and let
it seethe a good half hour; with the idea of separating the
glue-like matter (wherewith the particles seemed to be
stuck to one another) by so doing, in order that I should
the better be able to view the parts themselves.
Now when the stuff which I had taken off my tongue
had lain in the water, in which it was boiled, for about
a fortnight,’ I saw that the water was well-nigh evaporated
away; so I poured again a little rain-water, which had
stood some days in a clean phial in my closet,’ into the
boiled water aforesaid. And five or six days afterwards,
1 Brom Letter dated 29 June 1708. To the Royal Society. MS.Roy.Soc.
Not published in Dutch or Latin editions. English translation (incomplete)
printed in Phil. Trans. (1708), Vol. XXVI, No. 318, pp. 210-214. I
translate from the MS. in L.’s own hand.
2 A reference to a letter dated 18 Oct. 1707. MS.Roy.Soc. Incomplete
English translation in Phil. Trans. (1707), Vol. XXV, No. 312, p. 2456
[misprinted 1456]. Not published in Dutch or Latin.
® een schoon jndiaanse Coffe Copje MS. ‘‘a clean China Coffee-dish ”’
Phil. Trans.
* ontrent veertien dagen MS. “above a Fortnight”? Phil.Trans.
> op mijn Comptoir MS. “upon my Desk near the said boil’d Water ”
Phil. Trans. Cf. p. 114 supra.
LETTER OF 29 JUNE 1708 255
I brought a thin glass tube suddenly with its one open
end over the bottom of the porcelain cup, where most of the
particles that had come off the tongue lay all of a heap; ’
with the idea that when the water entered the tube, a few
particles from the tongue would also be carried upwards
into the tube, so that I should thus again be enabled to
view the particles off the tongue: in doing which,’ I saw
an inconceivable number of exceeding small animalcules,
and these of divers sorts. But far the greatest number
was of one and the same bigness, yet this was so little
that they could not be discerned but by great attention,
through a very good magnifying-glass ; and most of these
animalcules were abiding* where the said matter from
the tongue lay, and I took into consideration whether the
sald creatures might not indeed be getting their food from
the particles of the tongue. And when these animalcules
had been in the glass tube for about two hours, I perceived
that a great many of ’em were dead.
1 over hoop lagen MS. In the Phil. Trans. the translator transferred
the adverb to the glass tube, making L. say that he “ hastily turned it
upside down [my italics] into the bottom of the China Cup.”
2 in welk doen MS. ‘and it happen’d as I wished” Phil. Trans.
* haar . . . waren onthoudende MS. “ rendezvous’d ” Phil. Trans.—
a good translation, but not a word that L. would have used.
256
CHAPTER 4
THE LATER OBSERVATIONS ON FREE-LIVING
PROTOZOA
(LETTERS 122, 125, 144, 147, 149, 150, VII, X XIX)
Leeuwenhoek in his’ multifarious protistological
wanderings during the last quarter of the X VII Century.
We have yet to consider his equally remarkable excursions
into similar unexplored fields at a later date.
At the turn of the century—when he was already an old
man, nearing his 70th birthday—he was still, despite his age,
at the height of his powers; and during the next few years—
between 1700 and 1716—he recorded some of his most
interesting protozoological discoveries. These observations
were all made on free-living forms found in water.
In a letter written at the very beginning of 1700,
Leeuwenhoek gave the first description and picture of
Volvoz. The letter’ begins with an account of other observa-
tions, and describes inter alia some gnat-larvae which he had
found in ditch-water.? It then proceeds :
Ie the three preceding chapters we have followed
IT had got the foresaid water taken out of the ditches
and runnels on the 30th of August:* and on coming
1 Letter 122. 2 January 1700. To Sir Hans Sloane. MS.Roy.Soe.
Published [Dutch] in Brieven, III, 152 (2nd pagination), Sevende Vervolg
(1702): [Latin] in Opera Omnia (Epist. Soc. Reg.), III, 146 (1719) : English
translation in Phil. Trans. (1700), Vol. XXII, No. 261, p. 509.—Curiously
enough, Vandevelde entirely overlooks the fact that this letter contains the
first description of Volvoz.
2 These observations are also remarkable: for they show that L. had
noticed the difference in posture of Anopheline and Culicine larvae in the
water—a peculiarity now well known, but generally supposed to have been
discovered by recent malariologists.
* Anno 1698, as appears from the earlier part of the letter.
LETTER 122. 2 sanuaRy 1700 257
home, while I was busy looking at the multifarious very
little animalcules a-swimming in this water, I saw floating
in it, and seeming to move of themselves, a great many
green ' round particles, of the bigness of sand-grains.
When I brought these little bodies before the micro-
scope, I saw that they were not simply round, but that
their outermost membrane was everywhere beset with
many little projecting particles,” which seemed to me to
be triangular, with the end tapering to a point: and it
looked to me as if, in the whole circumference of that
little ball, eighty such particles were set, all orderly
arranged and at equal distances from one another; so
that upon so small a body there did stand a full two
thousand of the said projecting particles.
This was for me a pleasant sight, because the little
bodies aforesaid, how oft soever I looked upon them,
never lay still; and because too their progression was
brought about by a rolling motion; and all the more
because I imagined at first that they were animalcules.
And the smaller these little bodies were, the greener in
colour they appeared to me: whereas contrariwise, in
the biggest (that were as big as a coarse grain of sand)
no green colour could be made out in their * outermost
part.
Each of these little bodies had inclosed within it 5, 6, 7,
nay, some even 12, very little round slobules,* in structure
like to the body itself wherein they were contained.
While I was keeping watch, for a good time, on one of
the biggest round bodies, among the others, in a little
water, I noticed that in its outermost part an opening
' groene ronde deeltjens MS. ronde deeltjens Dutch printed version
“reat round particles” Phil. Trans. Groene (green) is very important ;
and “great” is an obvious mistranslation or misprint. The Latin version
also omits “‘ green ’’—calling them simply particulae rotundae.
2 ¢e., the individual flagellates composing the colony.
* het MS. haar printed version.
* i.e., the daughter-colonies.
Li
258 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”?
appeared, out of which one of the inclosed round
globules, having a fine green colour, dropt out, and took
on the same motion in the water as the body out of
which it came. Afterwards, the first round body ' remained
lying without any motion: and soon after a second
globule, and presently a third, dropt out of it; and so
one after another till they were all out, and each took on
its proper motion.”
After the lapse of several days, the first round body
became, as it were, again mingled* with the water; for I
could perceive no sign of it.
What also seemed strange to me, was that I* could
never remark, in all the motions that I had observed in
the first round body,’ that the contained particles ° shifted
their positions; since they never came in contact, but
remained lying separate from one another, and orderly
arranged withal.
Many people, seeing these bodies a-moving in the water,
might well swear that they were little living animals; and
more especially when you saw them going round first one
way, and then t’other.
Now when a great many of the said round bodies were
in a bottle along with many little living animals, I saw
that after the space of three days they were all gone,
inasmuch as I could then make out none of the said
bodies in the bottle.
Moreover, I had put a few drops of water (as shown
at CD [Plate XXVI1]) in a glass tube (Fig. 1, AB) about
1 j.e., the mother-colony.
2 en yder een beweginge aannam. These words are in the printed version
but not in the MS., and were probably added in the proof as an afterthought.
* <.e., the mother-colony broke up. The word is vereenigt [=united] in
the MS., but was changed to vermengt [=mixed ] in the printed version.
* The word ik—which is necessary for the sense of this passage—is here
present in the MS. but omitted in the printed version.
° 4,e., the mother-colony.
* «.e., the individual flagellates composing the colony.
7b) J ad { i ‘ ; a iat
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1 as ‘
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XXVI
PLATE
‘UOI4ZIpS Yoon, oy} surAuBdMIODNv SSUIABISUO BYy WOAT
(OOLT “URE Z
‘GGL ON) vodjo4, NO UALLAT SMAOHNAMNAAT OL SNOILVULSOATII
259
9
facing p.
DISCOVERY OF VOLVOX 259
eight inches long, and of the thickness of the quill of a
hen’s feather." One end (A) I left open, the other end (B)
I plugged with a bit of cork (so that betwixt D and B
there was nothing but air), with the idea that” when I
came to handle the tube, the water wouldn’t run out of it.
The air being now shut up in the tube, between D and B,
cannot remain of the same volume, or extent, but changes
at every moment, so to speak; for one can’t approach the
tube with the hand, the breath, or any part of the body
that is a little warmer than the air wherein the tube is
lying, without the air in the tube being affected by some
part of it; and this warmth brings about an expansion
or greater enlargement of the air (in the tube), whereby
the water is made to move, being driven from DC towards
A: notwithstanding we may perceive no motion in it
with our naked eye. And just as the least warmth
causes this outward displacement of the air in the glass
tube, so likewise warmth readily departs from the tube,
whereupon a movement of the water takes place* back
from C towards B.
In this water were included two of the foresaid round
bodies,’ and these of the biggest sort; and contained in
each of them were five little round particles,? which
inclosed particles were pretty well grown in size: and in
a third big body there lay seven round lesser particles.
These last were uncommon small.
After the lapse of four days, the said round bodies
remaining shut up in the glass tube all this while, I
perceived that in two of them the outermost membrane
1 een schagt van een hoender [MS. honder] penne Dutch edition “of a
Goose Quill” Phil. Trans.
2 dat is here accidentally omitted in the MS., but restored in the printed
version.
3
aan neemt MS. is nemende printed version.
* j.e., mother-colonies.
° i.e., daughter-colonies.
260
LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
(which was become exceeding thin and clear) was * burst
asunder; and that the ten particles, that were contained
within the two big bodies, were moving about in the
water, rolling first one way and then the other.
Furthermore I perceived,’ after the space of five days,
that the small particles inclosed in the third large body
were not only grown in bigness, but I could also then
discern that from inside these small particles other lesser
round particles* were to come forth. After the lapse of
five days more, this third round body was also a bit burst
open, and its contained particles were also come out of it:
but notwithstanding it was open on one side, it kept on
going round in the water, and that as quick as it had
done heretofore.
Some days afterwards, I could make out nought but
some little bits whereof the bigger bodies had been
composed ; and soon after, these too went out of sight.
Without a break I continued from day to day to watch
these little particles that had issued from the bigger
ones; and I always saw that they not only waxed in
bigness, but that the particles contained within them got
bigger too.
At the end of September,’ I perceived that the con-
tained particles were not so regularly round as the bigger
bodies wherein they were inclosed, and therewithal that
some of them were broke apieces ; and that the last particles
that were come out of the big ones seemed not to be round,
and lay without motion against the glass.’
1 waren MS.—corrected to was in printed version.
2 dat (redundant) stands here in the MS., but has been removed in the
printed version.
* j.e., daughter-colonies within the daughter- colonies. This acute
observation gave great support to the doctrine of the “ preformationists ”’ at
a later epoch, though it was then usually accredited to Spallanzani—who
merely repeated and confirmed L.’s observations.
* Anno 1698.
> The whole of the foregoing sentence is inexplicably omitted from the
Latin version.
REPRODUCTION OF VOLVOX 261
Now these last bigger bodies, when they had unbur-
dened themselves of their contained particles, or when
they broke asunder, were quite four times less than those
wherefrom they issued: wherefore we may conclude that
they had not reached their full growth, or gotten their
right food.
We have also noted that the said round bodies agree
in their weight with water.’ This being so, they may be
set in motion in the water with the least movement that
it recelveth from the air.
I thought fit to have one such body pictured, with its
contained particles; as shown’ in Fig. 2,at EF. In this
body, the inclosed round particles (which had so waxed in
bigness that they were ready to be cast out) did not lie in
such recular order as they did in those before described ;
and as in this one there was not so continuous a motion,
I imagine that this was simply due to the contained
particles not all lying at an equal distance from the centre,
so that the round body was heaviest on the side where the
particle furthest from the centre was placed, whence its
motion was somewhat hindered.
For what purpose these round bodies are created we
know not. But as I observed that the various round
bodies, when mixt with a great many little animals* in
the big bottle, were all vanished in the space of three
days, I did well ponder whether they were not created to
serve as food for such little animals.
Now as we see that the oft-mentioned round bodies
come into being not of themselves,* but by generation, as
we know all plants and seeds do (inasmuch as every seed,
1 i¢., have the same “specific gravity’? as water. This term was
unknown, of course, to L., though the concept was familiar; and I
therefore render his words literally and not too “ scientifically”.
spontaneous generation ’’.
2 See Plate XXVI.
L. here means mosquito-larvae, crustacea, ete., —not protozoa.
. ee . oe
* niet wijt haar selven—meaning “not spontaneously”, or not by
262 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”
be it never so small, is as it were endowed with its
inclosed plant‘); so can we now be more assured than we
ever before were heretofore * concerning the generation of
all things. For my part, I am fully persuaded that the
little round bodies, which are found in the bigger ones,
serve as seeds; and that without them these big round
bodies couldn’t be produced.°
In the summer I divers times applied myself to the
study of the waters lying around our town, the last
occasion being on the 8th of October 1699: but I could
satisfy myself no further in this matter.
The remainder of this letter contains no other observations
on Protozoa: and the next reference to any of these organisms
occurs some five months later, when Leeuwenhoek very briefly
mentions and depicts the shell of a Foraminiferan, which he
had found in the stomach of ashrimp. He did not, of course,
know that it was the shell of a protozoon: but as this is the
only mention—so far as I am aware—of any Rhizopod in the
whole of his writings, I will quote the passage. After
discussing the anatomy of the shrimp, he describes what he
had found in shrimps’ stomachs, and adds:
In some of their stomachs I also discovered very little
snail-shells, which, because of their roundness, I called
1 Demonstrated by L. elsewhere.
2 te vooren . . . tot nog toe—redundant in the original.
* The foregoing description of Volvox, though perfectly intelligible in the
original, is somewhat obscured by the circumstance that L. uses the same
word (deeltjens=particles) throughout to denote the mother-colonies, the
daughter-colonies, and the individual flagellates. To make his meaning
plain I have therefore substituted “ body”’, " bigger particle ’ ’, ete., for
‘particle”’, where it is necessary to distinguish the “ particles’’ of different
categories. The Latin translator took a like liberty with his original, and
rendered deeltjens by particulae rotundae, particulae majusculae, particulae
minores, etc., aS occasion required.
“ From Letter 125. 2 June 1700. To Frederik Adriaan, Baron van
Rhede: [Dutch] in Brieven, Tde pete p. 196 (1702) ; atoll in Opera
Omnia (Epist. Soc. Reg.), II, p. 186 (1719). No MS., and not in Pail.
Trans. The Latin translation is wrongly dated January 2 (postridie Kal.
Jan. 1700). An English version of the letter will be found in Hoole (1807),
Vol. II, p. 266—the passage cited being on pp. 271-2.
PLATE XXVII
TWO OF LEEUWENHOEK’S FIGURES ILLUSTRATING LETTERS 125 AND 144
Enlarged from the original engravings.
Fig. 7, ABC.—Shell of a Foraminiferan (Polystomella ?).
Fig. 3, PQ.—The Ciliate Coleps. (The original measures only 6 mm. in length.)
facing p. 263
LETTER 125. POLYSTOMELLA 263
little cockles;* and these little shells were no bigger
than a coarse sand-grain.
In order to exhibit the pretty structure of these little
shells before the eye, I thought ’twould not be amiss to
set a drawing made of one of them. Fig. 7, ABC
[Plate XX VII] shows one of these little cockles, which
I took out of the stomach of a shrimp.
It has been generally agreed that the shell here referred
to was that of a Foraminiferan, but different writers have
interpreted its species variously. For my part, I feel fairly
confident that the picture represents a Polystomella.’
Leeuwenhoek’s next contribution to protozoology is
imbedded in a _ well-known letter dealing chiefly with
Rotifers: and the protozoological elements in this epistle
have, it seems to me, been hitherto largely ignored or mis-
understood. Too my mind there can be little doubt that he
here left us an unambiguous record of his discovery of three
different Protozoa—two Phytoflagellates (Haematococcus and
Chlamydomonas) and a Ciliate (Coleps). But I will leave
him to speak for himself: °
On the 25th of August,’ I saw that in a leaden gutter,’
on the front of my house, for a length of about five feet
1 ven slakhoorntje. Hoole translates “snails”, but Sewel (1708) says
the word denotes ‘a Cockle-shell’’; and from L.’s allusion to their
roundness, I take this to be correct. The Latin translator called them
limaces cochleares.
2 Cole (1926, p. 13) takes the same view; but Miall (1912, p. 216)
identifies the organism as Nonionina. Robert Hooke (1665, Obs. XI, p. 80;
Scheme V, Fig. X) had previously described and figured a foraminiferan
shell—probably Rotalia—which he had discovered in sand: but to L. his
observation was apparently unknown.
* Letter 144. 9 Feb. 1702. To Hendrik van Bleyswyk. Brieven (7de
Vervolg), III, 400; Op. Omn. (Epist. Soc. Reg.), III, 380. No MS. and not
in Phil. Trans. Partially translated into English by Hoole (1807), IJ,
207.—Vandevelde says this letter is a “ Beschrijving van waterdiertjes,
wellicht infusorién”’: but neither he nor anybody else appears to have
sorted out the various “Infusoria’’ described, though Biitschli (Vol. II,
p. 621) recognized Haematococcus.
* Presumably anno 1701.
> John Ray (in 1663) notes as a curiosity that in Holland “the Rain
ce
264 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
and a breadth of seven inches, some rain-water had
remained standing, which had a red colour; and as it
occurred to me that this redness might well be caused by
red animalcules (as I had indeed seen come about in
muddy ditches), I took a drop or so of this water and
looked at it through the microscope; and I discovered a
creat many animalcules* that were red, and others that
were green, whereof the biggest looked no bigger through
the microscope than coarse sand doth to your naked eye,
and others smaller and smaller, each after its kind.
These animalcules were for the most part round, and
the green ones were somewhat yellowish in the middle of
their bodies.
Their bodies seemed to be composed of particles that
presented an oval figure; and therewithal they had short
thin instruments which stuck out a little way from the
round contour, and wherewith they performed the motions
of rolling round and going forward ;* and when they took a
rest, and fixed themselves to the glass, they looked like a
pear with a short stalk; but this stalk,’ on curious examina-
tion, was split at the end, or divided into two, and ’twas
with these two parts that the animalcules fixed ’emselves
fast to the glass.”
that falls upon the Houses is by Pipes and Gutters conveyed into a Cistern,
and there reserved for the uses of the House, as at Venice in Italy.” It
would appear, therefore, that gutters were not commonly installed on
English houses at that date. (See Ray, 1673; p. 53.)
1 The description which follows obviously refers to the Phytoflagellate
Haematococcus pluvialis (=Sphaerella lacustris), which is very commonly
found in gutters. This is the first account of this organism. The smaller
green ones were probably, for the most part, Chlamydomonas—equally
common in this situation: vide infra.
2 waar medeze een omwentelende beweginge en voortgang te weeg bragten:
“by means of which they caused a kind of circular motion and current in
the water’—Hoole. This mistranslation entirely spoils the sense of this
important passage describing the action of the flagella.
® Hoole here interpolates “or rather this tail’—which is not in the
original, and shows that he did not understand what L. was talking about.
* This is a remarkably good observation of the locomotory organs of
Haematococcus, which possesses two anterior flagella that often adhere to
one another for a variable length at their proximal ends.
LETTER 144. 9 FEBRUARY 1702 265
The smallest animalcules of this sort I judged to have
been begotten of the bigger ones.
I did also see yet another kind of animalcules, that
were much smaller.’ These were very clear in the body ;
but I judged that there must have been quite a hundred
of the former sort to every one of the latter.
On the 31st of August, the water was so far dried up
(owing to the great heat, which had continued for three
days running), that if I pressed my finger on the dirt”
lying on the lead, little more than a drop of water as big
as a sandgrain stuck to it: and though I could discern a
few living animalcules, which were transparent, in this
water, yet all the green and red ones were dead.
On the Ist of September, the stuff in the leaden gutter
was become so thick, that it was like stiff wet clay; and
notwithstanding all my efforts, I could discover no living
creatures in it of the sort that I had seen before.
At this point Leeuwenhoek leaves Haematococcus and goes
on to describe the Rotifers which he also discovered in his
leaden gutter; but in the course of his description he
accurately notes that:
The stuff in the guts of these little animals ° was most
always red, proceeding (as I imagined) from the red
animalcules* which they use as food: but I also saw
afterwards a few of these little animals which hadn’t
any of the red stuff inside them, particularly the young
ones which had not long left their mother’s body.
Here follow further observations on Rotifers—including
the famous experiment in which Leeuwenhoek found that
1 Possibly bacteria, but obviously unidentifiable from this slight
description.
2 A little later (4 Nov. 1704) L. says—in the words of a contemporary
English translator (MS.Roy.Soc.)—* I don’t suffer such foul stuf to lye long
in my gutter, but twice a year cause the lead to be scowered so clean that
it looks just like new’”’.
* t.e., Rotifers.
4:
2.€., Haematococcus.
266 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”
they can “‘return to life” after desiccation. Whilst relating
his experiences, however, he mentions an organism which is
almost certainly identifiable—from the figure which he
fortunately gives—as the ciliate Coleps. He says:?
Now divers little animalcules came before the draughts-
man’s eye, whose structure was very like what is shown
in [Plate XX VII] Fig. 3,’ between P and Q, whose belly
was flat, and from which little instruments stuck out,
wherewith it effected its progress. And as this animal-
cule had little round globules in its body, so there were
yet many other little animals * a-swimming in the water,
whose whole body seemed no bigger, under the micro-
scope, than one of these globules in the bigger sort just
spoken of.*
I have divers times so placed the said animalcules’ out
of water, that they were encompassed by an amount of
water not so big as a sand-grain; in order to see whether
these little creatures, when all the water round them was
evaporated away, and they were lying in nothing but air,
would burst asunder, as I had made certain of in other
animalcules:° and I saw that whenas the water was
1 Brieven, III, p. 407: Op. Oman. III, p. 387.
* In the figure as copied by Hoole (II, Pl. XVI, fig. 35) the resemblance
to Coleps is largely lost. The original—though very small—shows quite
clearly the characteristic barrel-like form (with one side somewhat flattened)
of this organism. The expanded anterior end (bearing the terminal mouth),
the caudal spines, and even the four girdles of armour-plates, are all clearly
indicated. Biitschli noted the resemblance to Coleps, but considered the
identification as doubtful. To me it appears certain.
* Possibly bacteria—or perhaps flagellates.
“ These two sentences are very clumsily constructed in the original—
though their meaning is clear enough—and I have not attempted to improve
them.
* de verhaalde dierkens. It is not absolutely certain that this expression
means the organisms just mentioned : it possibly refers to the Rotifers. If
it really refers to the Protozoa, then the ensuing words confirm the view
that L. was here describing Coleps; for this ciliate has a cuirass composed
of numerous interlocking platelets, which prevent its bursting when dried.
° Cf. Letter 18, p. 120 supra.
COLEPS. GUTTER-WATER 267
almost exhaled, and the animalcule could no longer turn
and twist itself about in it, it took on an oval figure, and
stayed lying thus, without my being able to see that the
moisture evaporated away out of the creature’s body, for
it kept its oval figure.
At this point Leeuwenhoek returns to his experiments with
the Rotifers: but in the account of their revivification after
drying he notes that he
also saw two several sorts of little animalcules
a-swimming through the water, whereof the least were so
little, that many thousands together would not equal a
coarse grain of sand in bigness.’
After some further remarks on Rotifers he then says:
Once more we see here the unconceivable Providence,
perfection, and order, bestowed by the Lord Creator of
the Universe upon such little creatures which escape our
bare eye, in order that their kind shouldn’t die out.
From these discoveries we can well understand that in
all falling rain, carried from gutters into water-butts,
animalcules are to be found; and that in all kinds of
water, standing in the open air, animalcules can turn up.
For these animalcules can be carried over by the wind,
along with the bits of dust floating in the air: and on the
other hand, animalcules which are a hundred million
times and more smaller than a coarse grain of sand, can
be borne aloft, along with the water particles, albeit not
as high as the clouds, but at least a little way up; and
then when the sun goes down, they fall to earth in what
we call dew; and they may well be taken up too and
carried along by the wind. This is the more probable,
since we know that in a storm the sea is so lashed on the
shore by the wind, that drops of sea-water are found on
trees, running down their trunks, and still salty, more
than half-an-hour’s journey from the coast. This salt
" Lit. cit., Brieven III, p. 409. These were evidently not Rotifers but
Protozoa or Bacteria.
268 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”
water is judged by the vulgar (though mistakenly) to be
the salt evaporated by heat from the sea.’
On the said* 4th of September, it rained a little while
at eventide; yet so much fell, that in the leaden gutter
aforesaid there was some water on the 5th and 6th of
September: and this water I examined on both days,
and discovered, in every drop that I took from the gutter,
eight or ten of the animalcules described, though I could
not discern a single one of the round green or red creatures
that was alive.
On the 6th of September, I put up seven glass tubes, in
which I placed some of the dry stuff aforesaid out of the
leaden gutter; pouring into some of them boiled, and
into others unboiled rain-water.2... On the 7th of
September I viewed the said glass tubes, and beheld with
wonder in one of them an inconceivably great number of
little green animalcules,* all alive, all of which seemed
round, as before described, and a-moving among one
another ; nay, I saw so many that the very water seemed
to the naked eye to have a faint green colour: but how
curiously soever I examined the other glass tubes, I could
find no living green animalcules in them... .°
On the 9th of September it rained a little; and two or
three days later it rained so much, that on the 14th of
September there was water to the depth of about a finger’s
breadth in the leaden gutter. Of this water I took
about two drops; and examining it, I saw a great many
of the little round animalcules previously made mention
* dat door de warme wytwaseminge van de Zee werd voortgebragt. These
words were omitted by Hoole—also most of what follows.
2 Mentioned earlier, in connexion with Rotifers, in a paragraph not here
translated. Apparently anno 1701.
* I here omit two lines referring to Rotifers.
* There can hardly be any doubt that these organisms were Chlamy-
domonas. In similar experiments I have always obtained this flagellate in
abundance.
° Further observations on Rotifers are here omitted.
CHLAMYDOMONAS AND HAEMATOCOCCUS 269
of, whereof most had the outermost part of their bodies a
pale green, and the middle of the body quite red.’
On the 15th and 29th of September, on the 13th and
27th of October, on the 25th of November, and the 9th of
December, I continued my observations aforementioned ;
steeping the said stuff* both in new-fallen rain, that was
collected in an East-Indian porcelain dish, and in boiled
and ordinary rain-water: whereof I kept notes. But as
the upshot was always one and the same, I discarded
these notes: and I will only say that, on the day last
mentioned, I put some boiled water, when it had got
nearly cold, with a little of the oft aforementioned
dirty stuff, into a glass tube that was sealed off at one
end, and stopt with a cork at the other, and carried it
about in my pocket: and I found some hours afterwards
that not only the big animalcules* . . . were swimming
in the water, but also many others so small, that they
looked through the microscope no bigger than a dot, such
as you might make with a pen. And when I had carried
this glass tube in my pocket for eight days, these last-
mentioned animalcules were so increased that there were
some thousands of them, both fixt on the glass and
a-swimming in the little quantity of water.
On the 8th of February,’ when the oft-mentioned stuff
had lain for a few days more than five months upon
a clean white paper in my closet, I put a little of it intoa
clean glass tube, and poured boiled rain-water, after it
had cooled, upon it: and after the space of about halt
an hour, I already found one animalcule swimming about
in the water, and many others that remained still rounded
up; and three hours later I saw various others of this
kind, and some small ones of a different make.”
_ ee ee ee) ee ee ee
1 Undoubtedly Haematococcus.
? i.e., the dry deposit in the gutter.
® There is a reference here to the figures, which shows that these big
forms were Rotifers.
* Presumably 1702.
® Possibly Protozoa.—These observations were referred to again by L. in
sé
270 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”
Now since we see that these animalcules can lie bedded
so long in dry matter, as before described, and then on
coming into water can swell out their bodies, and swim
off; we may therefore conclude that in all pools and
marshes, which have water standing in them in winter,
but which dry up in summer, many kinds of animalcules
ought to be found; and even though there were none at
first in such waters, they would be brought thither by
water-fowl, by way of the mud or water sticking to their
feet and feathers.’
Seeing these wondrous dispensations of NATURE,
whereby these little creatures are created so that they
may live and continue their kind, our thoughts must be
all abashed; and we ask ourselves, Can there even now
be people who still hang on to the antient belief that
living creatures are generated out of corruption ?
About a couple of months after the foregoing lines were
written, Leeuwenhoek sent the Royal Society some further
observations on the animalcules occurring in rain-water.
The following is a translation of the greater part of this
letter : °
his Letter XXIX (5 Noy. 1716, to Boerhaave); Send-brieven, p. 288 (published
1718). Vide p. 297 infra.
1 These remarks recall a well-known passage in The Origin of Species,
where Darwin discusses the dispersal of organisms by similar means.
2MS. 28 April 1702. To the Royal Society. Not published in Dutch
or Latin works. English version (abbreviated) printed in Phil. Trans. (1702),
Vol. XXIII, No. 279, pp. 1152-1155 [where the date is wrongly given as
1701]. I translate from the original Dutch MS. According to my numera-
tion this is Letter 147: but Vandevelde (1924, p. 132), who did not detect
the error in the date as printed in the Phil. Trans., calls it “‘ Brief 2 Tr 1
[137a]”. The MS. of the English version is extant, along with the Dutch
original, in the Royal Society collection, and is in the hand of John
Chamberlayne.—Chamberlayne (1666-1723) was a miscellaneous writer
and translator—said to have been conversant with 16 languages—who was
educated at Oxford (1685) and Leyden (1688). He became a Fellow of the
Society in 1702, and translated—as will appear presently—several of L.’s
other letters for publication. His best known work—Magnae Britanniae
Notitia, which went through many editions—was a rescript of a smaller
book by his father, Edward C. It contains an interesting account of the
Royal Society—among many other things.
LETTER 147. 28 aprit 1702 271
On the 19th of September, 1701, it rained a little
while about noon, whereupon I caught some of the
rain-water, as pure as I was able to, in a clean East-
Indian porcelain dish :* putting this water then in a glass
tube, in order to see whether, in such new-fallen rain, on
standing in my closet, any living creatures would turn up.
I examined this water several days running, and dis-
covered therein many little bits of dust, otherwise called
particles, such as generally float in the air, consisting of
very little bits of burnt wood, or charcoal, wherein I
could make out the horizontal and ascending vessels;
also a little bit of straw, and many blackish particles
which I imagined to be congealed particles out of smoke
from the coals that our smiths and brewers burn: and
among these was a pretty structure” composed of round
globules clotted together, just lke the little stars that
we see in the snow in winter. But I could discover no
living creature till the 28th of September, when I dis-
covered some exceeding small animalcules that were
fixed to the glass, or anon swam forwards with a quivering
motion ; which afforded me no unpleasant spectacle.
These animalcules were so small, that I could only
make them out by very nice scrutiny; the tube, in which
the water was, being so big and thick; but especially
because the animalcules seemed to me as clear as glass:
but it looked to me as though their bodies were twice as
long as the width of their thickest part,’ the foremost
and hindmost parts of their bodies running somewhat to
a point.
z ‘in a fine China
in een suijvere gndiaanze porsteleijyne schootel MS.
Bason’”’ Chamberlayne.
2
‘
een aardig maaksel MS. ‘an odd Phenomenon” Chamberlayne.
* hare lighame twee maal soo lang waren, als deselve op haar dikste sijn
MS. “twice as long as they were big’? Chamberlayne.—The organisms
were probably flagellates, but are obviously unidentifiable. Their attachment
to the glass suggests Monas vulgaris, which would also fulfil the other
requirements of the description.
272
‘
LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS ”’
Yet from the 10th of October till the 14th of the same
month, I could perceive no living creature, how carefully
soever I looked. But whereas I had till now always
examined only the uppermost part of the water that was
in the glass tube, on the 15th of October I inspected very
narrowly the bottom of the glass tube (which was four
inches long, and had a diameter of a third of an inch):
and there I saw very many of the animalcules aforesaid,
both fixed upon the glass and swimming forth; and
many others sat so still upon the glass, that you might
think they were not animalcules at all; but when one of
’em moved, among the crowd, several others next to it
did too.
Not being content with these my observations, because
I misdoubted me whether there might not well have been
some water in this tube previously, and that from this
source these animalcules had come, and had remained
fixed to the glass, before I poured this rain into the glass
tube: in order to satisfy myself hereof, I procured a glass
tube that had lain full twenty years shut up in a dry
chest, and whereof I was assured that neither the least
water, nor anything but air, and what is therewithal
contained in it, could have gotten into it.
On the 18th of October it rained in the forenoon, after
we had had several days of strong and stormy wind: and
I once more caught the rain in the porcelain dish, and
after flinging away the first two lots received in it, I
poured the third lot of water into the glass tube.
This last water I viewed many times ; but how curiously
soever I looked, I could make out no living creature in it,
though I saw particles stuck to the glass, that agreed in
bigness and figure with the animalcules aforesaid : till the
24th of October, when I discovered three animalcules that
were running along and swimming forward against the
glass, and not in a straight line, but with bendings and
turnings as they went along: and the day after, I
discovered like animalcules in quite ten different places,
ANIMALCULES IN RAIN 213
both running forward and swimming, and that as
plain as if you saw, with your bare eye, those little
animals that the common man calls Water-fleas, swim-
ming in the water.’
Now there lay against the glass, within the compass of
a coarse grain of sand, more than a hundred particles
that were of the bigness of the foresaid animalcules,
which particles I divers times viewed one day, to discover
if possible whether any living creature would come out of
them,’ or turn up thereabouts; but how carefully soever
I looked, yet could I discern no living creature among
these particles, nor those lying hard by: until the
28th of October, when I saw, among the particles last
mentioned, a good five-and-twenty animalcules swimming
forwards, as well as running upon the glass: and I did
then discern two sorts of animalcules,® whereof the
smallest appeared to me first shining, and then not
shining: and their shininess, so I imagined, was observable
whenas they swam with their back or uppermost part of
the body turned towards my eye. These last animalcules
had a quite different motion, in swimming forward, from
those a bit bigger. As regards the particles that were
fixed to the glass, I couldn’t see any change in ’em.
I examined the said water for several days running,
and I saw the smallest animalcules in such great plenty,
both coursing upon the glass and swimming, at every
spot where I cast my eye, that ‘twas amazing: and as I
was holding the microscope in one hand, and in the other
the glass tube (in which the water, owing to the width of
the tube, was set in motion),* I invariably perceived that
1 op het water MS. “in the ordinary Brooks and Canals ’’ Chamberlayne
—a picturesque but inaccurate rendering of the original.
2
‘
ut de selve . . . soude voortkomen MS. “whether they were
living Creatures’’ Chamberlayne.
* Probably protozoa, but not identifiable.
* i.e., by the warmth of his hand, producing convection-currents.
18
274 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
when the animalcules were aswimming, and got off some-
what from the glass, they were borne forward, as if they
were not strong enough (as you might say) to swim up-
stream: yet they alone made, as they went ahead, certain
windings, while the bits of dust in the water (which were
very big in comparison with the animalcules) were swept
forward in a straight line.’
I have also made sure that, when I put new-fallen rain
in a glass tube in which there was never before any
moisture, shortly afterwards very many little air-bubbles
made their appearance in it, and remained sticking to the
glass: but a little while later these air-bubbles were gone.
T'o satisfy myself further hereof, on the 6th of November
I took once more a new glass tube, and examined it
through the microscope: but notwithstanding I had very
carefully shut it up, and covered it over, I saw that there
were yet many very little bits of dust in it. On the
6th of November it rained again, and I caught the rain,
as before described, and put it in the glass tube; in order
to see whether in this one also the air-bubbles would
make their appearance, and whether they would then
vanish from sight.
I examined this water divers times, even after it had
been four hours in the tube; in which time I could
discover not more than two or three air-bubbles, which
were on a dried-up mite,’ out of which the air seemed to
issue.
But whereas I had stood the former glass tube upright,
and had put another one down somewhat aslant, I now
placed this last glass tube lying almost flat, only so that
the opening lay a bit higher, lest the water ran out of it,
' This passage is paraphrased by Chamberlayne, though its import is
correctly conveyed. It can hardly be doubted that L. was here able to
distinguish the animate from the inanimate particles.
2 ven wijt gedroogte mit MS. ‘‘a dry Particle” Chamberlayne. I do
not know whether the “mite’’ should be interpreted literally or
metaphorically.
OBSERVATIONS ON RAIN-WATER O15
and that the air-bubbles might keep the position that
they had at the top of the glass; and after the lapse of
ten hours I saw a great many air-bubbles, that were
mostly affixed to the said dust-particles. And forasmuch
as we know that no dry matter or any other particles, in
which air is included, when they get under water can
then get the water into them unless the air be first dis-
lodged, so the same held good also for the particles that
were in the glass tube.
But what is one to say of this, that some of the air-
bubbles were quite a hundred (and others several hundred)
times bigger than the particles on which they were
stuck ?
Next day, in the morning, I perceived no more than
four very little air-bubbles, and a few hours afterwards I
couldn’t find a single one.
I examined this water every day till the 14th of
November, but could discover no living creature in it;
and the day after, I had the mischance to let my tube
drop, so that it was smashed to bits.’
It is not possible to identify the organisms mentioned in
the foregoing letter, though some of them must certainly have
been protozoa. At the end of the year, however, Leeuwenhoek
wrote a very important epistle in which he described and
figured several freshwater protozoa which are easily recog-
nizable. This letter is so important, indeed, that I must
translate almost the whole of it. It is addressed to the Royal
Society, and runs as follows: ’”
1 The remainder of this letter deals with other subjects, and is therefore
omitted.
2 Letter dated 25 December 1702. To the Royal Society. MS.Roy.Soc.
Not printed in Dutch or Latin editions. English translation in Phil. Trans.
(1703), Vol. XXIII, No. 283, pp. 1304-1311. (The MS. of this translation
is also extant, and is in the hand of John Chamberlayne. See p. 270,
note 2, supra.) According to my numeration this is Letter 149. Vandevelde
numbers it ‘‘ Brief 2 Tr 3 [147] ”.—I have made my translation from the
original Dutch MS., but have compared it with Chamberlayne’s and note
one or two points in which his version differs.
276
LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS”’
I take the liberty of informing you, Gentlemen, that I
have oft heard the common people say that duckweed’,
which floats on the water, is generated in the ground
underneath.
I could not allow of the truth of this assertion; for
whenever I examined duckweed, I always found that one
of these plants is produced by another, as with trees and
other vegetables.
Whenever I turned my attention to duckweed, I always
noticed that it never grows in deep water, even though
the water be small and stagnant, and without motion,
save such as is imparted to it by the wind’; but it is
seen in great plenty on broad sheets of water, which are
not deep and have little motion, but especially in narrow
and shallow ditches.
I have also observed that in ditches wherein there is
very little water, the duckweed is very small, in com-
parison with that which is found on big sheets of water,
along the banks, where the water is shallow and has but
little motion.
Delfshaven, belonging to our Town, lies about two
hours’ distant from it; and from here, through a sluice
from the River Maas, the water that runs through our
town is let in with the flood in summertime, and this
water is then as clear as though we had the River Maas
itself here.
Now with this running water there is brought in, from
time to time, a little duckweed ; yet so little, that ’twould
take you half an hour to collect thirty little weeds in a |
pot all at once. I got some of the duckweed scooped out
of this water, in an earthen pot, with lots of water, so
that their roots might not be hurt.
I took several of these little weeds out of the pot of water
' het kroost MS. (alibi Eende kroost)=“ Lens palustris” of the old
writers = Lemna of modern botanists.
ge
‘and that the Wind does it no harm’’ Chamberlayne. This is a
mistranslation.
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PLATE XXVIII
Philor: Transa t:M:9 84:
ILLUSTRATIONS TO LEEUWENHOEK’S LETTER ON THE ANIMALCULES
FOUND ON DUCKWEED (25 Dec. 1702)
Reduced from the engravings published in Phil. Trans. (1703). (In the
original drawings, in red crayon, the figures are reversed.) Figures re-
numbered to agree with original account.
facing p. 277
LETTER 149. 25 DECEMBER 1702 O77
with a needle, one after the other, as nicely as I was able
to, and put them in a glass tube of a finger’s breadth,
that was filled to the top with water, and also in a
smaller glass tube, and suffered their little roots to sink
down gently; and then examining these roots with the
microscope, I beheld with wonder many little animals
of divers kinds, which escape our naked eye; whereof
two sorts had long tails,* wherewith they were linked fast
to the little roots of the duckweed. In structure these
little animals were fashioned like a bell, and at the round
opening they made such a stir, that the particles in the
water thereabout were set in motion thereby, so that on
but two occasions was I able to discern the little instru-
ments* with which they brought about this motion. And
though I must have seen quite 20 of these little animals
on their long tails alongside one another very gently
moving, with outstretcht bodies and straitened-out tails ;
yet in an instant, as it were, they pulled their bodies and
their tails together, and no sooner had they contracted
their bodies and tails, than they began to stick their tails
out again very leisurely, and stayed thus some time
continuing their gentle motion: which sight I found
mightily diverting.
I got drawings made of some of these animalcules, as
they appeared when fastened to the root of a bit of duck-
weed. [See Plate XXVIII.*|
Fig. 1, ABC shows a bit of duckweed of ordinary
bigness, as it looked, when lying out of * ne water, to the
ne eye of my ME elAneTE,
1 Vorticellids. Cf. p. 118 supra.
2 ““T could not see those instruments. ... Chamberlayne. This is
not a correct rendering. L. says “soo dat ik maar twee maal hebbe
geste .: .”
* The figures on the Plate in Phil. Trans. were renumbered 6-12 (other
illustrations having been added); but I have here altered their numbers to
agree with L.’s original drawings and descriptions. Fig. 7 [12] depicts a
leaf of duckweed not mentioned in the passages here translated.
* buijten het water MS. “upon the water’? Chamberlayne.
278 LEEUWENHOEK AND HIS “LITTLE ANIMALS”’
Fig. 2, DEFG shows this duckweed with its little roots,
as it floated in a glass tube filled with water, whereby the
roots are displayed.
Fig. 38, HIKLMNOPQR shows a little piece of the
root of a duckweed, as it appeared to the draughtsman
through the microscope; in which rootlets you could
discern the vessels, with their divisions, running long-
ways along the root; and these rootlets (so I imagine),
when’ they are of no further use, and as it were withered,
get overgrown with very many peculiar long particles,
mostly forming little figures that you might call “flowers”,
as shown here for a short distance in Fig. 3, between K
aad: A
The animalcules aforesaid, that I have likened unto
little bells, are shown in Fig. 3, between IST * and NVW,'
whereof I have seen, upon some roots, even more than a
hundred living, attached by their little tails, within a
space such as HIKLM, Fig. 3; though upon other roots
I discovered none.
And I also saw fixed upon several roots one or even
(though very seldom) two little cases,’ of various sizes,
whereof the biggest is shown in Fig. 3, RXY. Out of
this little case a little animal, with a small part of its
body which looked roundish, made its appearance, as in
Fig. 3, XZY: and thereupon there suddenly came out of
SSS EEE
‘“‘\vhen”’ is here omitted by Chamberlayne, who thus gives a slightly
different turn to this passage.
2 Diatoms and monads.
* Carchesium polypinum—with branched (contractile) stem. Previously
mentioned by L. in Letter 96. See p. 211 supra.
‘ A group of 3 solitary individuals of Vortzcella sp.
° Kokertjens MS. From the description and figures it is clear that the
biggest organism here spoken of is not a protozoon but a tubicolous rotifer—
almost certainly Limnias ceratophylli. It is certainly not Melicerta (from
which L. clearly distinguished it), nor can it be Cothurnia (as Ehrenberg
and others have stated). This ciliate is described a little later. The “little
wheels ” were, of course, the cilia on the two lobes of the trochal disc—so
interpreted by all early observers of Limnzas.
7
VORTICELLIDS AND ROTIFERS 279
its roundness two luttle wheels, which displayed a swift
rotation, as shown in Fig. 3,a@bc. (The draughtsman,
seeing the little wheels going round, and always running
round in the same direction, could never have enough of
looking at them, exclaiming’ “O that one could ever
depict so wonderful a motion!”’) These little wheels
were as Closely beset with teeth, or cogs, as the wheel of
a watch might be: and when these animalcules had
thus performed their motions for some time, they pulled
their little wheels into their body again, and their body
right into the little case; and soon after they brought a
part of their body out of the case again, with the motions
aforesaid ; and at another time they would stay a long
while inside the case, as though shut up in it. But
although I had, indeed, formerly discovered such little
wheels on other animalcules” too, yet their bodies were
different from these, and their cases were of a dark nature,
so that you couldn’t easily make out the animalcules in
them; and therewithal they seemed to be composed of
pellets.
And I also saw some cases that were several times
smaller than that just mentioned, and these * were as
clear as glass, so that you could see the little creatures
lying within them quite distinctly. Fig. 3, Pdef, shows
the case, with the animalcule Pdf, occupying a part of it,
as it lay taking a rest. Fig. 3, ogh, shows the little case
1 konde men soo een wonderbare beweginge altijd vertoonen MS. “‘O,
that he could always see such a wonderful kind of motion’”’ Chamberlayne.
I take it that the artist’s wish was to be able to portray (vertoonen) this
motion—not that he might go on looking at it for ever. Regarding the
artist himself, see p. 343 sq., onfra.
2 Melicerta ringens. In later letters (MSS. 4 Nov. 1704, to Roy.Soc.,
and 28 June 1713) L. gives an admirable description of this rotifer, and
describes how it builds its house. See Phil. Trans. (1705), Vol. XXIV,
p. 1784: also Letter VII (Dutch and Latin works) and Phil. Trans. (1713),
Voleex VIET; p:.160:
* Bvidently not rotifers but tubicolous ciliates (Cothurnidae)—probably
the common Cothwrnia cristallina, though the species cannot be determined
from the description and figures.
280 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS”
with the animalcule as it looked when it stuck part of its
body (gh) out of it, at which time alone you could now
and then just make out the two little wheels,’ because of
their exceeding smallness, but only when its body was
straightened out, for otherwise it lay drawn up short.
Further, I discovered a little animal * whose body was
at times long, at times drawn up short, and to the middle
of whose body (where I imagined the undermost part of
its belly was) a still lesser animalcule of the same make
seemed to be fixed fast by its hinder end. Such alittle
animal, because of its wonderful structure and manner of
propagation, I have had drawn, and at least twice as big
as it looks to the naked eye when you see it in the water
and attached to the root of a bit of duckweed. Tig. 4,
ABCDEFG, shows this creature, whereof A is the hind
end that it hangs on by, while at CDE are shown its
eight * horns (though others a bit smaller had six horns),
as it looked when it had straightened itself out, for other-
wise it can scarce reach to a quarter of this length; and
its horns seemed to my eye to be made in so marvellous
a manner, that the draughtsman’s art isn’t competent to
portray them, though the artist did his best to draw a
small bit of a horn, as shown at KLM in Fig. 5.
In Fig. 4, at BH, is shown a little animal that is coming
out of the first one; and formerly, when I saw such a
little animal fixed to a bigger one, I imagined that it
was only a young animalcule attached by chance to a big
one; but by nicer attention to the matter, I saw that it
was a reproduction: for I observed that whereas the
second animalcule, at the time when I first recognized
that it really was one, had only four very short little
1 A misinterpretation of the peristomial cilia. In Cothurnia it is very
common to find 2 individuals (the products of fission) in the same house.
2 Hydra—the first description of this organism.
* The draughtsman—as will be evident—inadvertently depicted nine
tentacles instead of eight: ef. Plate XXVIII, fig. 4.
HYDRA DISCOVERED 281
body and its horns had increased in bigness, and four
hours later still I saw that it had forsaken its mother.
When I discovered the young animalcule aforesaid, I
also perceived that, on the other side of the body of the
first animal, there was situated ' a little round knob, which
J did see getting bigger, from time to time, for the next
few hours (as shown in Fig. 4, between G and I); and at
last it appeared as a little pointed structure, which had
so far grown in bigness in the course of thirteen or four-
teen hours, that you could make out two little horns
upon it. After the lapse of another four-and-twenty
hours, this last-mentioned animalcule had four horns,
whereof one was small, a second a bit bigger, and the
other two much bigger; and these last the little animal
stuck out at full length, or pulled in short. And another
three hours later this little animal was gone off from his
mother. *
I tried to trace this reproduction further, and for this
purpose took the duckweed away from the animalcule, so
that I could follow it better; but next day that animal-
cule not only lay dead, but its horns and a piece of its
hind end were all gone, having rotted off, as you might
call it.
Another little animal, that had brought forth two young
ones, not only had her body laden with many other
1
aan de andere zijde .. . een rond knobbeltje zad MS. I take this
last word to be a verb (zat=sat). Chamberlayne, however, evidently
took it for a substantive (zaad = seed), and consequently translates ‘a round
little knob of seed”. But I cannot reconcile this interpretation with the
construction of the sentence as a whole, and at this period L. always spelt
zaad (=seed, a frequent word with him) with aa—never “ zad”. ‘A knob
of seed”’ is also an unintelligible expression. Dr A. Schierbeek (in. litt.)
agrees with my interpretation.
2 All the foregoing observations on the budding of Hydra are very
remarkable. No animal which reproduces asexually by budding was known
at that date; and the sensation caused by the similar observations of
Trembley, and others, nearly half a century later, is in strange contrast
with the apparent indifference which greeted L.’s discovery.
ce
bo
OO
bo
LEEUWENHOEK AND HIS “LITTLE ANIMALS”
animalcules’* (which are flat beneath, and roundish above,
and which I have discovered in most other kinds of water,
and which are hardly a thousandth of the size of the
animals which they crawl on with their little feet, and
cause annoyance to); but a much bigger sort of animal-
cules ° whose bodies were roundish, so pestered one of
these little animals, not only getting on her body, but also
by clinging on to her horns, that in spite of all the struggles
she made with her horns and body, she couldn’t shake it
off; and I noticed afterwards that the little animal had
lost one of her horns.*
“ What seemed to me remarkable and wonderful,
was that these little animals would oft-times let down
their horns so far, that you would think, on seeing them
through the microscope, that they were several fathoms
long.
At one time or another I let the draughtsman have a
look at the horns as they were being stretched out, or
anon pulled in; and with me he was forced to exclaim
‘What wonders are these!” For as the creature pulled
in its horns, they became perfectly round, and the closer
they got to the head, the thicker they became, and when
they were pulled right in, they formeda still bigger round
blob.
I charged the draughtsman to draw, as well as he was
able to, a small part of a horn when so stuck out, which
is here shown in Fig. 6, NOP. On this part are shown
' Evidently the “common polyp-louse”’, Trichodina pediculus.
2 The “large polyp-louse”, Kerona. The ciliates ectoparasitic on Hydra
were again studied and described at a much later date by Rosel von
Rosenhof, Trembley, Baker, and others. This is the earliest account
of them.
* “in the scuffle’ is added here by Chamberlayne—a_ picturesque
addition, but not authorized by L.’s own words.
* T have translated the remainder of L.’s remarks on Hydra because they
are so entertaining : they contain no further observations on protozoa. But
Hydra, rotifers, and protozoa were all “ animalcules ” for L., and he did not
separate them zoologically ; so his views on one sort are illustrative of his
notions about all.
HYDRA AND ITS “ LICE” 283
the knot-like lumps, which are to be seen also in Fig. 5,
KLM. These lumps look to me as though they were
made up of seven round globules; to wit, one in the
middle, which sticks up a bit above the others, and the rest
lying round it in a rosette.
Now if we consider what a lot of instruments must all
be contained in a little piece like Fig. 6, in order that it
may be not only stretched out, but also drawn in, and
moved around, and with as many bends and knots in it too
as you might make in a piece of string; so must we
wonder all the more at such a contrivance. And who
knows but what every knot-like part may not also itself
be furnished with yet other organs, whereby they are set
in motion. Seeing these things I was put in mind of the
knotted threads over which people have spent so much
time these last few years:* and I said to myself, If the
ladies of our country could see such a wonderful and
perfect structure, would they not have reason to bewail
the time and gifts which they employ in making such a
lot of useless knots, in which not the least bit of art or
beauty is ever to be seen!
I saw in this water, or on the duckweed, many wonderful
animalcules, some of them getting their food from it, and
others (as I imagined) using it as a skulking place, to
avoid being devoured by little fishes: but the weed seemed
only calculated to show off’ the three sorts of animalcules
aforesaid.”
' This apparently refers to some kind of macramé-work in which L.’s
countrywomen then indulged: but I have been unable to find any other
reference to it in contemporary writers.
2 maar voor genomen de drie verhaalde dierkens aan te wijsen MS. I take
the above to be L.’s meaning. In his view, everything in nature was created
for some purpose ; and I suppose he would have said that one of the purposes
of duckweed is to accommodate and display animalecules such as Vorticella.—
The last words of the above sentence were omitted by Chamberlayne—
possibly because he could not understand what they meant.
* L. here describes the duckweed itself, and its generation, at greater
“ec
284 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
Whilst observing this last weed, I saw with wonder a
creat many animalcules’ swimming in spirals through
the water, and they were in such a great number together
in so small a space, that they looked like a little cloud,
visible to the naked eye, in the water; and animalcules
of this sort I have never before seen in other waters, but
on the second day they were nearly all gone.
Furthermore, in this water there were so many sorts of
animalcules that I had never discovered in any other
waters, that I was mazed to see such a diversity of
structures; and each too had its own proper motion,
wherefore I many times looked upon these delightsome
and wondrous little creatures, which quite escape the
bare eye.
During these observations, I saw one sort that exceeded
many of the others in bigness, which were coupled
together,” in which act they lay very still against the
glass, unless a bigger sort came too near them: and as
they lay still, you could leisurely discern those instru-
ments wherewith they can so swiftly move themselves,°
and even the motions of certain parts in their bodies, from
which some would certainly conclude that they saw the
circulation of the blood ;* but I would sooner take it for
the chyle’ in the guts. These animalcules were so big
that you could descry them” in a glass tube, with clear
length. As this part of the letter—though very interesting—-is irrelevant
to the present subject, I have omitted it, and resume the translation at the
point where the animalcules are again referred to.
’ Probably protozoa, but unidentifiable.
? Probably ciliates conjugating. Cf. pp. 200, 205, 206, 213, supra.
* Cilia, in all probability: but possibly cirrhi.
“ This reference to the internal “circulation” is puzzling, unless L.
actually observed the cyclosis of the food-vacuoles (in non-conjugating
individuals) or the rhythmic pulsation of the contractile vacuoles.
° A modern reader might perhaps consider chyle here to be a mistake
for chyme: but in L.’s day these terms were often. used synonymously. Cf.
Lexicon Medicum (Blankaart, 1748; p. 192)—‘‘cHYMUS, idem est quod
”
chylus’’.
® j.e., with the naked eye.
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PLATE XXX
philos :Transacttl -228¢
LEEUWENHOER’S FIGURES OF Anthophysa vegetans
From the engravings in Phil. Trans. (1703), illustrating his Letter of 5 Feb.
1703. (The original drawings, in red crayon, are reversed.) Slightly
enlarged.
facing p. 289
ANTHOPHYSA VEGETANS 289
And now I also saw that upon the extreme tips of a
very few of the branches there were three or four, or
sometimes even five, round globules, set beside one
another like a rosette; which afforded no unpleasant
spectacle. For when one such branch was fastened to
the glass by its thick end alone (from which all the other
lesser branches sprang), then all the twigs’ were put in
motion by any little movement which you imparted to
the water ; whereby also some of the aggregated globules,
which were set thereabouts, and which you would judge
not to be stuck fast upon the utmost twigs, were’ like-
wise put in motion: but I assured myself, after divers
observations, that they were really fastened thereto,
though I could make out no structure whereby they were
joined, owing to its exceeding thinness.”
I let the water run very slowly out of the glass tube, in
order that the branches (which were fastened to the glass
by their stem, and whose twigs were kept in continual
motion when one handled the tube) might lie against the
glass, as the water ran off them, so that my draughtsman *
would thus be able the better to make a pipeure of them.
[See Plate XXX. ]
Fig. 1, ABCDEF, shows the structure described, as it
was lying against the glass. A represents the part that
you would put down as the root of a plant, whereby
alone ‘twas fastened to the glass. We see here what a
lot of twigs there are on it, which now look rather
disorderly ravelled together, though lying free in the
water they were not unpleasant to behold: especially
because their colour was like that of oaken wood, and in
many places they were encrusted with little round
1 alle de sprankjens MS. Chamberlayne says “all the five small
Twigs’; but this is not in the original, and does not make sense.
2 IT supply waren, which is missing in the original—apparently owing to
the presence of the same word in the clause immediately preceding.
* This sentence is much condensed in Chamberlayne’s translation.
* Cf. p. 342 infra.
19
290
LEEUWENHOEK AND HIS “ LITTLE ANIMALS”’
cranules, just as if they were made up of congealed round
particles.’
At G, and hard by D, are shown the rosette-like struc-
tures which seem to consist of several globules, and
whereof some are also indicated at H: and though I
couldn’t see that the structures shown at H were joined
to twigs, yet they always moved about in the water in
the same way as the utmost little twigs did.
No sooner was the water poured out of the glass tube,
than I forthwith viewed the structure aforesaid: and
thereupon I saw swimming, between the twigs called BD
and BE, two animalcules as small as each of the globules
whereof the structures shown at H are made up: and
these animalcules then went on swimming, even in the
little water that had not yet evaporated from between
the twigs, till my eye wearied with looking at them.
During this observation I further saw one of the four
globules shown at H break off, and make off as though
swimming away, though the distance of its removal was
not above a hair’s breadth: and this particle which swam
off was certainly an animalcule, for it turned and twisted
itself round about several times. And in another globule
I did also see indeed a little motion ; but it didn’t break
off from the others, with which it formed the figure of a
rosette.
There were, furthermore, many other little bough-lke
structures which did not lie so orderly: and when the
water ran off them, they took on the shapes shown in
Fig. 2, IKL, and Fig. 3, MNO.
What are we to say about the fabric of these little
boughs, or tree-like growths? We can’t suppose that
they proceed from a seminal matter in the water: but,
with submission to better judgements, we are more
satisfied by imagining that they are composed of some
substance which, floating in small particles in the water,
1 The stalk of Anthophysa is encrusted with brown particles of ferric
hydroxide, and this is by no means a bad description of its appearance.
ANTHOPHYSA DISCUSSED 291
is clotted together by some kind of mutual attraction.
This won’t seem strange to us, if we bear in mind that
whenever we file a bit of iron it gets rather hot; and if
we apply the filed part to the filings, they’ll stay hanging
chain-wise from it; though in nothing like the way
such filings do with a lodestone.
At this point Leeuwenhoek digresses into a description of
some chemical experiments. ‘Then, after describing how he
dissolved a little metallic silver in dilute nitric acid, he tells
us how he witnessed the wonderful branching “ tree” which
grew in this solution when he dropped into it “a particle of
copper of the bigness of a sand-grain.” Such “trees” are
now familiar to every schoolboy, but in Leeuwenhoek’s time
they were novelties: nor has their wonder been wholly
evaporated away by the work of modern chemists.’ It is
clear, moreover, that Leeuwenhoek saw in the metallic “tree”
a physical analogy—suggesting an explanation of its growth—
to the ‘“‘tree” of Anthophysa, formed (in part) by the con-
gealed particles of ferric hydroxide: for he adds ‘‘ I observed
with a great deal of pleasure, how the Silver in this clear
Water was coagulated into such bodies as are described by
the above-mentioned Trees”’.*” Nevertheless, while recognizing
the resemblances, he confesses that the process of growth is,
in both cases, to him “ wholly inscrutable ”’.
About 10 years later Leeuwenhoek sent another most
interesting letter to the Royal Society—a letter in which he
described anew his observations on Rotifers and Vorticellids.
After referring to his previous observations on Melicerta, and
its ciliary mechanism, he says :°
1 Cf. Leduc (1911).
® Chamberlayne’s translation.—L. gives a figure of his “ silver tree ”’
which is, I believe, the first ever published. His observations are, apparently,
unknown to Leduc and other recent students of similar phenomena.
° From Letter VII. 28 June 1713. To the Royal Society. MS.Roy.Soc.
Published in Brieven, IV, 64 (1718); Epist. Physiol. (Op. Omn. IV), p. 63
(1719). English translation printed in Phil. Trans. for 1713 [published
1714], Vol. XXVIII, p.160. (The MS. of this translation—in an unknown
hand—is preserved in the Roy. Soc. collection.) I translate directly from
the original MS. in L.’s own hand.
292 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS
Notwithstanding I have so many times seen such
animalcules,’ and let others see ’em too, yet one can’t be
satisfied with just looking at* so wonderful a structure:
chiefly because one can’t get clear on how such an
unbelievable motion is brought about, and in the second
place, as to what purpose this motion was for. For when
we see any part of such a creature (that is endowed with
motion *) moved,* we feel sure that this part wasn’t made
for nothing, but is a necessary part of it; and conse-
quently this wheelwork is of use to the animalcule’s body,
though we can’t call to mind just what use it is.’
He then records some further observations on Rotifers—
made “at the end of July and the beginning of August
[1712] ’—and proceeds :
Furthermore, I paid great attention to their revolving
toothed wheelwork; and I saw that an incredibly great
motion was brought about by the said instrument, in
the water round about it, whereby many little particles,
that could be made out with the magnifying-glass, were
wafted towards the animalcule, while others were carried
away from it; whereof some, being borne into the middle
of the revolving instrument, were used as food by the
animalcule.’ And other particles, when they got up to it,
went off from the animalcule as quick as if it flung them
away; seeing which, I came to the conclusion that the
cast-off particles were no good to the creature for food.
From this observation we may well conclude that, since
1 Called Dierkens throughout in the Dutch printed version, but Dieryens
in the MS.
* te beschouwen: these words are in the printed version but not in
the MS.
° The words in parenthesis are in the MS. but not in the printed version.
4 bewegen MS. dat bewogen werd printed version.
° 4s printed version was MS.
5 van het Dierke als tot spys gebruykt wierden Dutch printed version.
The MS. says het Dierke als tot spijs gebruijkte (the animalcule used as
food).
LETTER Vil. 28 JunE 1713 293
these animalcules can’t displace ’emselves' in the water,
they can’t” chase after their food, like all* other creatures
do that are endowed with motion, so that they can get
from place to place.’
These animalcules,’ then, and all the others too, that
can’t shift ’emselves from place to place, either because
they are fixt by the tail, or otherwise, must be furnisht
with similar instruments, in order to make a stir in
the water; whereby they get any stuff that is in the
water for their food and growth and for the defense°
of their body.’
And when we observe the animalcules that are fixt by
a long tail*® to something or other, like many that we have
discovered on the little roots of duckweed,’ we see that
they don’t merely go round in a circle with the extreme
part of their body “ (whereby they make, in proportion to
the littleness of their body, a big bustle in the water) ; but
the creatures can also pull their tails together, and that
very quick too; so that when they stick their tails out
again, they displace the water round about them, and
1 Underlined in MS. but not italicized in printed version.
2 There are slight verbal differences here between the MS. and the printed
version, but they do not affect the sense.
3
alle is in Dutch printed version, but not in MS.
* The Latin version adds “ whenever they want to” (quoties libet): but
this is not in the Dutch.
° Soin MS. The Dutch printed version has “ animals” (Dieren).
S Referring to the pellets with which—as he had just described—
Melicerta builds its house. :
’ This passage is worded differently in the MS. and in the printed
version, but the sense is identical. In the Phil. Trans. the two foregoing
paragraphs were condensed into a single sentence.
* i.e. Vorticellids.
° Of. p. 277 sq., supra.
” L. means that the body of the Vorticellid travels in a circle round
the point of attachment of the stalk. The Latin translator apparently
misunderstood these words, which he rendered “ extremitates corporis sui in
orbem complicant’’.
294 LEEUWENHOEK AND HIS “LITTLE ANIMALS ”’
being thus come into different water,’ they can get fresh
food out of it.
Now I also saw a very few animalcules’ (whose bodies
were short and thick), that were much bigger than the
animalcules that make a little case for their dwelling-
place,’ and these were fixed to the little roots of the
duckweed by their hindmost or tail-like part; and not-
withstanding they were able to move from place to place,
they also made none the less a circular motion with the
foremost part of their body: whence I also concluded
that such a motion was for no other purpose than to
make anything that would serve as food come towards
them.*
I have ere now asked myself, What is the use of such
a toothed wheelwork, like a cogged wheel out of a clock ?
But if we now let our thoughts run on further, we must
decide that such a thing is necessary, if a great stir is to
be made in the water: for if it were a round and smooth
wheel, it would make little motion in the water; whereas
now every tooth that sticks out from the circumference
causes a great stir in the water, in comparison with a
smooth and even rotation.
This being so, we are faced once more with the
mysteries, and unconceivable order, which such tiny
creatures (which quite escape one’s naked eye) are
endowed with.
1 Underlined in MS., but not italicized in printed versions. The phrase
is rendered in Phil. Trans. “and so bringing fresh Water under them,’—
which is incorrect.
2 Clearly unidentifiable from this meagre description, but probably
rotifers.
* Referring to Melicerta (and the tubicolous ciliates ?). The word here
translated “ dwelling-place”’ is in the original hwysvesting, which may mean
“ edification ” in any of the literal or metaphorical senses which this word
has in English.
“ “From whence I concluded, that those Motions serv’d some other
purposes than only to draw their Food to ’em.” Phil. Trans. The
translator here completely reversed the sense of L.’s words.
CILIARY MECHANISMS 295
Can anybody doubt, after reading the foregoing words,
that Leeuwenhoek had, in 1718, already discovered the chief
function of the peristomial cilia (“ wheelwork”’) of Vorticella ?
Surely not. Old Antony knew as well as I do (and everybody
else now does) how the Vorticellids, and many other ciliated
organisms, capture their food from the surrounding water—
though he misconceived the structure of the mechanism. By
persistent study he had advanced a long way beyond his
original interpretations of 1676,‘ and had at last reached the
truth.
The remainder of this letter contains some further observa-
tions on “‘animalcules”’: and as some of these—though none
is exactly identifiable—were undoubtedly protozoa and
bacteria, I will now quote what else he here relates : °
At the beginning of the month of August,’ I was in a
garden where there was a pond well stocked with fish ;
and pretty well all over the water there floated a thin
scum, which looked greenish, though you couldn’t see any
other green-stuff in the water: which seemed to me odd,
because in other years* I had noticed that the water was
very clear in this pond, as it was also in the ditch from
which the pond was continually replenished; but I was
told that when it rains, the scum goes away.
I went a little aside, all on my own, and took a wooden
lath, with which I touched the surface of the water ; and
putting a little drop of the water in a green wine-glass, I
looked at it through a microscope that I had by me: and
I discovered in this water so unbelievably many little
animalcules, which even through a microscope are scarce
discernible, that no one could be made to credit it, unless
he got a sight of it for himself; and also divers sorts of
1 Cf. p. 118 supra.
2 The passages which follow begin at the top of p. 68 of the Dutch
printed works (Vol. IV, Send-brieven).
* Presumably anno 1712: but from the final paragraph this is not
certain.
* op andere jaren MS. “at other times”? Phil. Trans.
296 LEEUWENHOEK AND HIS “LITTLE ANIMALS”
large animalcules, mixt with very’ many air-bubbles, of
extreme littleness.
A few days’ afterwards, I asked to have a little of this
water brought to my house, in order to examine it more
nicely ; but I could discover nothing else in it than what
I have just related, though I noticed a little later that
no air-bubbles * were to be seen in it.
Now if people rinse beer and wine glasses in such a
pond, who can tell how many animalcules may be left in
these glasses ? whence some of them may even get into
our mouths. And this being so, people have no reason
to ask me how the little animalcules, which, as I have
said many a long year ago,’ are in the stuff between our
teeth, and in hollow grinders,’ are able to get there.
Thus far my notes, which I kept some years ago, and
which I have come across within these last few days.
Leeuwenhoek’s last recorded observations on protozoa are
contained in a letter written in 1716 to Boerhaave.° Unfor-
tunately they are mentioned very briefly—being sandwiched
in between observations and speculations on spermatozoa.
Despite their brevity, however, they are of extreme interest.
After speaking of the spermatozoa of various animals,
Leeuwenhoek abruptly interjects the following remarks: ‘
1 The word “very” (seer) is in the printed version, but not in the MS.
* Eenige dagen MS. Eenige weynige dagen Dutch printed version.
* Lugtbellen [underlined] in MS. The printed version has lugtbolletjes.
* Vide p. 238 sq., supra. The “ animalcules”’ were, of course, bacteria.
° inde stoffe . . . tussen onse tanden, ende inde holle kiesen [last
two words underlined] MS. “in and about our Teeth” Phil. Trans.
There are slight verbal differences here between the Dutch printed version
and the MS., though the sense does not differ.
®° Herman Boerhaave (1668-1738), Professor of Botany, Chemistry,
and Medicine at Leyden— ‘a whole Medical Faculty in himself’’—is too
famous a character to need further annotation. He was elected a Fellow of
the Royal Society in 1730. For his life see especially Banga (1868, p. 807)
and N. Nederl. Biogr. Woordenb. (1924), VI, 127 [a long and excellent article
by van Leersum J.
” From Letter XXIX. 5 November 1716. To Boerhaave. Published
in Brieven, Vol. IV, p. 284; and (in Latin) in Opera Omnia, Vol. IV
(Epist. Physiol.), p. 279. No MS., and not in Phil. Trans.—The passage
here translated begins on p. 288 of the Dutch edition.
LETTER XXIX. 5 NOVEMBER 1716 297
I can’t forbear adding here, that I have allowed water-
animalcules, mixed with a little earthy matter, to lie dry
in my closet for a whole winter: and when I put them
again in water, I saw some of them unfold their limbs,
which seemed to be wrapped up inside them, and swim
about in the water.’ I have also observed that animal-
cules, which really belong to the waters, are to be found
in the soil in our meadows ;” and these animalcules are
carried thither, along with particles of water, by strong
winds, and come not only from the canals but even from
the sea. And notwithstanding that most of these
creatures are unable to stand the winter’s cold, and so die,
yet some of them survive, to propagate their kind: and
this has been their lot from the very beginning of things.
Then a few lines further on we strike the following gem:
Now I must tell you that there is, right at the back
of my house, a small flat lead, on which the rain-water
doesn’t dry up for several days after it hath rained. In
this water I have many a time seen, among others, some
very little roundish animalcules, of divers sizes, and
whereof the bodies were round, and having a diameter,
when full grown, of about thrice the diameter of one of
those globules that make our blood red: and in their
bodies you could distinctly make out four round globules.
These creatures were so vastly multiplied in a few days,
that I was dumbfounded at it.
I was all agog to know how this multiplication might
come to pass: and in the end I found out that these
animalcules lived for no longer than 30 or 36 hours, and
that they then fixed themselves upon the glass, and
stopped there without moving: while soon after, their
body burst asunder, and lay divided into eight portions:
" These were probably Rotifers, though some may possibly have been
encysted Ciliates.
2 This is probably a record of the first observations ever made on soil-
protozoa.
cc
298 LEEUWENHOEK AND HIs ‘‘ LITTLE ANIMALS ”’
and these were actually young animalcules, for in five or
six seconds some of them swam off.
Inasmuch as one animalcule thus begets 8 little ones,
and each of these again brings forth 8: then there would
be produced, in the course of 9 days, two hundred and
sixty-two thousand one hundred and forty-four animal-
cules from a single animalcule:
In 30 hours; or 13 (days, 70... 8 animalcules
8
cK opto eae © C7 Renee Pe 64 animalcules
8
in AF dayseese 512
8
in 6
1: Fae eRe OR 133; nearly <9 )-ucva oso.
1, TG) ene Meee 114) nearly:« <¢icccuansn ete 12996:
3. FAG ORES tien LOO 3s, sas Yay edo 10000.
3. Bera ht gessoi ag ck nal atlas 89! almost... cco useemes 7921 almost.
8. Sep wee eu eaayts er. SO. sat «cise nee 6400.
2. iro eC ee 72 something more... 5184 something more.
3. eh oes She = 66 nearly’... 5". «eas 4356 nearly.
2. Sea ota satet aie Diy! a Lay gsy chee eee 3249,
al Se (AE aoa ee ae BS mearly, i.) cucseasas ss 2809 nearly.
1. at Pee See a 40: ' 2S 2 ca eee 1600.
26
* This largest Magnifier of allis in the Box marked 25. [Note by Baker. |
Baker himself notes regarding these figures: “ I have given
the Calculations in round Numbers, the Fractions making but
an inconsiderable Difference; and I hope any Mistakes I may
have made in so nice a Matter will be excused”. I must also
note—since it has been generally overlooked—that all the
magnifications are given for an image-distance (8 inches)
which is not the “common standard” now universally adopted
(10 inches). Consequently, all Baker’s “magnifying powers”’
represent only ~ of the actual magnification according to
modern notation: and therefore the “largest Magnifier”, with
nn
1 Baker (1740), p.506. The later description (Baker, 1753; p. 436),
though that usually quoted, gives far less detail.
320 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
a focal length of 3G in., magnified not 160 but 200 diameters
according to present-day reckoning—and so on throughout.
After a somewhat lengthy discussion, Baker reaches the
conclusion that Leeuwenhoek’s best microscopes, with which
he made his most considerable discoveries, “ must certainly
have been much greater Magnifiers than any in our Possession”’
—a conclusion which was then well founded.
I need not give Baker’s illustrations of a Leeuwenhoek
microscope—which have often been copied—nor their accom-
panying description,’ for more instructive data are now avail-
able: but I must here quote some other contemporary records
which throw more light on the present subject.
It is well known that Leeuwenhoek left many microscopes
with his daughter when he died. Apart from the 26 bequeathed
to the Royal Society there were some hundreds of others—
though their number is generally misstated. Maria did not
sell any of these instruments, but preserved them all her life.
After her own death (1745), however, they were put up for
auction and dispersed. Copies of the sale-catalogue (1747)
are still extant ; but the late Professor P. Harting, of Utrecht,
possessed a unique example which is of the greatest interest
and on which he has left some valuable notes’. I shall
therefore here translate his words verbatum, as they contain
information now unobtainable elsewhere. In 1850 he wrote: *
I have in my possession two copies of the catalogue
of Leeuwenhoek’s microscopes, drawn up for the auction
which took place on Monday the 29th of May, 1747.
One of these copies was probably used by the notary or
auctioneer at the time of the sale, for it is interleaved
with white paper on which the names of all the buyers,
and the prices fetched by the instruments, are carefully
recorded. The catalogue is got up rather more luxuriously
than is customary at the present day; for it is printed
1 Baker (1753), pp. 434-436; Plate XVII, figs. VII and VIII. (Dutch
edition [1770], pp. 453-456; Pl. XVII, afb. 7 & 8.)
* Haaxman (1875), p.38, has also described this catalogue, but adds
nothing material to Harting’s account.
* Het Mikroskoop, Vol. III, p.41 footnote. I have been unable to
discover what happened to Harting’s copies of the catalogue after his death.
LEEUWENHOEK’S MICROSCOPES 321
on heavy writing-paper, while a pretty allegorical copper-
plate engraving is placed at the beginning, along with
another displaying Leeuwenhoek’s portrait. The text is
in Dutch and Latin both.
From this catalogue it appears that Leeuwenhoek left
no less than 247 completely finished microscopes, each
provided with a lens, and generally also with an object ;
and, in addition to these, 172 lenses merely mounted
between little plates—419 lenses in all, therefore.
Among these lenses there are three made from so-called
‘Amersfoort diamond” (rock-crystal pebble)*; and of
one of the microscopes it is noted that its magnifying-
glass is ground from a sand-grain, while the object placed
before it is likewise a sand-grain. ‘T'wo microscopes are
specified as having two glasses, another three. It thus
appears that Leeuwenhoek also manufactured doublets
and triplets”; for, with his kind of apparatus, there can
obviously be no question of any proper compound micro-
scope. More than half of these microscopes (approxi-
mately 160) were mounted in silver. Among the rest
there are three made of gold—two of which weighed
10 engels* 17 grains, the third 10 engels 14 grains. One
of the former was sold for 23 florins 15 stivers, while both
the others were bought in. (This is probably the only
occasion on which microscopes have been sold by weight.)
The remaining microscopes were sold in pairs. The brass
ones fetched 15 stivers to 3 florins a pair, the silver 2 to 7
florins. The entire sale realized a sum of 737 florins and
3 stivers.t The names of the buyers show that all these
i.e. quartz. I know of no evidence to show that L. ever made
lenses from real diamonds—as is sometimes stated (e.g. by Nordenskidld,
1929 ; p. 165).
2 It now seems more probable that these were really double (or triple)
simple microscopes—i.e. 2 (or 3) single lenses mounted in the same frame
side by side—like the “double microscope” illustrated by Haaxman (1875)
p. 34, fig. 2A.
* An engels equals 32 grains: see p. 338 infra.
* About £61. 10s. in modern English currency.
21
1
322
LEEUWENHOEK AND HIS “LITTLE ANIMALS”
microscopes were purchased by Hollanders,' and it is
therefore surprising that one nowadays so seldom meets
with any surviving specimens of Leeuwenhoek’s instru-
ments in this country.
Elsewhere Harting has published a list of the objects
which Leeuwenhoek left fixed before his magnifying-glasses—
as mentioned in the sale-catalogue. Though they include
—like Folkes’s list—no protozoological or bacteriological
items, they seem sufficiently interesting to quote. According
to Harting, they were as follows: ”
Animal Objects
Muscle-fibres of a whale.
a 59 99 COdLish.
a ,, the heart of a duck.
Transverse section of the muscles of a fish.
Scales from human skin.
Crystalline lens of an ox.
Blood-corpuscles of a man.
Liver of a pig.
Transverse section of the bladder.
Bladder of an ox.
Papillae from the tongue of an ox.
Hair of sheep.
457 |, on DOAVEr.
» 9» elk.
wel Goss Dears
» out of the [human] nose.
Scale of a perch.
»” »” > sole.
Spinning-apparatus of a spider.
Thread [web] 999»
Sting ” 99 ”
Teeth » » ”
Hyes » ”
Spinning-apparatus of a silk-worm.
1 The names of all the purchasers (42 in number) have since been
printed in Harting (1876), p. 33.
2 Translated from Harting (1850): Het Mikroskoop, Vol. III, p. 465.
LEEUWENHOEK’S MICROSCOPES 320
Brains of a fly.
Optic nerves of a fly.
Tips of the feet of a fly.
Sting and sheath of a flea.
Feet » 9 99
HKyes of a dragon-fly.
» 99 beetle.
Sting of a louse.
MGM: 59 1 Sp of
Ovipositor ,, 5, aa
Red coral.
Section of oyster-shell.
Embryo oysters in a little [glass] tube.
Vegetable Objects
Transverse and longitudinal sections of elm-wood.
” ” ” ” » fir-wood.
»” ” ” »” »” ebony.
»” »” ” » »” lime-wood.
»” ” om) »” »” oak-wood.
” » ” ” » Clnnamon.
» » ” » »» cork.
” » ” 5) » rush.
Section of fossil wood.
Germ out of the seed of rye.
Vascular bundles out of a nutmeg.
Mineral Objects
Bits of white marble, rock-crystal, diamond, gold-leaf,
gold-dust, silver-ore, saltpetre, crystals, etc.
Harting was fortunately able to examine one of Leeuwen-
hoek’s few surviving lenses carefully: and as his tests are the
only recent ones made by an expert—so far as I am aware—I
must here note what he found. He reports* that the biconvex
lens which he studied was “really very good indeed”’, and
proved that its maker had attained “a very high degree of
proficiency in grinding extremely small glasses.” Its magni-
fying power was no less than 270 diameters [indicating a focal
1 Het Mikroskoop (1850), Vol. III, pp. 43, 44.
324 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
length of about 0°9 mm.]: and its resolution was so good that,
with suitable illumination, it was capable of resolving the 4th
croup of lines on a Nobert test-plate (7.e., a scale 10 » long
subdivided into 7 equal parts by parallel lines ruled with a
diamond on glass). In Harting’s opinion this was probably
the optical limit of Leeuwenhoek’s lenses: but the lens which
he studied was only one of hundreds, and some of the others
—now lost—may well have been superior.”
Leeuwenhoek himself has—to my knowledge ’—left us no
account of his particular procedure in making and mounting
lenses. Others published their methods,* but he never did.
How to grind and polish lenses for spectacles and telescopes
was common property, however, at the time when he wrote;
and it seems probable that he worked by the ordinary rules
and with the customary apparatus. If you had asked him
how to make a very powerful lens, of very short focus, he
would doubtless have told you that it could only be made by
the usual methods: but as such a glass would be much
smaller, and more convex, you would have to do everything
on a smaller scale, and pay more attention to details. If you
can make a good lens with a focus of 1 foot, then you can—
if you take pains, and know your job—make an equally good
one with a focus of +$5 of an inch. It is more difficult, and
takes longer; but that is all. It is a question only of the
time and trouble that you are prepared to expend. The
general methods of grinding and polishing lenses were no
secrets: and when Leibniz asked old Leeuwenhoek why he
did not educate a school of younger men in the art, he made
the following reply :”
1 Op. cit., Vol. I, p. 404.
2 The lens examined by Harting was in a microscope preserved, at that
date, in the physical collection at Utrecht. The instrument now in the
zoological collection of the same university is greatly inferior—its lens
having a focal length of about + in. (fide Mayall, 1886).
* Crommelin (1929), in his recent admirable essay on lens-grinding [and
lens-grinders] in the 17th century, is of the same opinion. On this subject,
he says, L. “has left us entirely in the dark’’.
* See especially Manzini (1660).
> Send-brief XVIII, pp. 168-9 [Epist. Physiol. XVIII, p. 167]. Letter
dated 28 Sept.1715. Not in Phil. Trans.
LEEUWENHOEK’S MICROSCOPES 325
To train young people to grind lenses, and to found a
sort of school for this purpose, I can’t see there’d be much
use: because many students at Leyden have already
been fired by my discoveries and my lens-grinding, and
three lens-grinders have gone there in consequence; to
whom the students have repaired, to learn how to grind
lenses. But what’s come of it? Nothing, as far as I
know: because most students go there to make money
out of science, or to get a reputation in the learned world.
But in lens-grinding, and discovering things hidden from
our sight, these count for nought. And I’m satisfied too
that not one man in a thousand is capable of such study,
because it needs much time, and spending much money ;
and you must always keep on thinking about these things,
if you are to get any results. And over and above all,
most men are not curious to know: nay, some even make
no bones about saying, What does it matter whether we
know this or not ?
In addition to Folkes’s and Baker’s and Harting’s des-
criptions there are many other brief accounts and figures
of Leeuwenhoek’s instruments. The first picture of his
“microscope” is that introduced into Verkolje’s mezzotint
(1686), in which Leeuwenhoek is depicted holding one in
his own hand (see Frontispiece). A similar piece of apparatus
is probably meant to be shown in the hands of the allegorical
personages represented in two of the engraved titles to his
works.' Baker (1753) gave, with his description, a couple of
poor diagrams which have been copied over and over again—
by Hoole (1807) and many others down to Disney (1928) and
Bulloch (1930) at the present day. Uffenbach (1754) also
pretended to portray ‘“‘ Leeuwenhoek’s microscope”; while a
small but excellent figure (from an unknown example) was
engraved on the title-page of the booklet by van Haastert
(1823). Other pictures—sometimes accompanied by descrip-
tions—are to be found in the works of Harting (1850),
1 See Ontled. & Ontdekk. (1686) = Anat. s. Int. Rer. (1687): Vizfde
Vervolg d. Brieven (1696) = Arc. Nat. Det. (1695). These engravings should
also be found (somewhere or other) bound up in all the Dutch and Latin
collective editions of L.’s letters.
“6
326 LEEUWENHOEK AND HIS “LITTLE ANIMALS”
Haaxman (1871, 1875), Mayall (1886), Locy (1910, 1925),
Sabrazes (1926), and divers other writers. ‘‘ Leeuwenhoek’s
microscope’”’ has even appeared in a recent film, in a modern
advertisement for a proprietary dentifrice, and in popular
periodicals—such as the Dutch illustrated weekly De Prins,
which lately published (38 January 1925) the best photograph
which I have yet seen.
Although Leeuwenhoek made and left many microscopes,
nearly all of them have long since disappeared. Not only have
those bequeathed to the Royal Society vanished without
trace, but even some of the few other examples mentioned
by Haaxman and Harting—still surviving in 1875—cannot
now be found. According to my friend Professor Crommelin
(1929a) only 8 specimens in all are now known to exist, 5 of
which are in Holland. Of these, 1 is in the Zoological
Institute at Utrecht, and 3 others were, until recently, in the
private possession of Mr P. A. Haaxman at The Hague: but
2 of the latter have now passed into the Historical Scientific
Museum at Leyden, and have thus become the property of the
Dutch nation.” (All three were exhibited at a congress in
Leyden in 1907. Cf. van Leersum, de Feyfer, and Molhuysen,
pp. 114, 115.) Iam informed that two other genuine instru-
ments are now in Germany—one in a well-known museum,
the other in the possession of an optical firm: but I have not
yet been able to verify these statements. I have also been
told* that the late Dr Henri Van Heurck, of Antwerp, had an
authentic specimen of Leeuwenhoek’s handiwork in his collec-
tion which was sold in 1914. The Nachet Collection (Paris)
also claims to possess one.* Neither in England nor America,
1 There seems to be a general suspicion—probably fostered by some
injudicious remarks of Saville Kent (Vol. I, p. 9, footnote)—that Baker, the
last man known to have handled these instruments, was in some way
responsible for their disappearance. This is entirely unjustifiable: for a
search through the Society’s records (made on my behalf by Mr A. H.
White, our learned librarian) has shown that we still possessed L.’s micro-
scopes long after Baker’s death. They vanished from the Royal Society’s
collection only about a century ago, and the few remaining records appear
to incriminate a very different person.
2 Cf. Crommelin (1929a).
* By Mr W. E. Watson Baker, who—with his father—valued the
collection before the sale.
* The Nachet Catalogue, I may remark, is grossly inaccurate in nearly
LEEUWENHOEK’S MICROSCOPES 327
however, is there any genuine specimen (so far as I have been
able to ascertain), though modern facsimile reproductions are
now in circulation in both these countries. These copies are
accurate, and some of them may before long be passed off as
authentic originals. More than one such exact facsimile was
made for the late Sir Frank Crisp, who preserved one example
in his private collection and presented another to the Royal
Microscopical Society of London (on 21 January 1914), in
whose rooms it can now be seen.’ Crisp’s own facsimile was
sold at Stevens’s in London on 17 February 1925, when
his collection was auctioned after his death.” Other similar
reproductions are also in existence. One was recently in
California, and a friend of mine (who saw it) states that its
owner assured him that he could obtain similar “‘ Leeuwenhoek
microscopes”’ at any time—for a price—from Holland. Be
this as it may, there are certainly facsimiles (and forgeries ?)
now on the market, and prospective purchasers should be on
their guard.
Most of the recent descriptions and pictures of “ Leeuwen-
hoek’s microscope” are based on the rather poor specimen
now preserved in the Zoological Laboratory at Utrecht. The
best account and figures*® of this instrument are, I think,
those of Mayall (1886): but as I am not wholly satisfied with
his or any other description or pictures (Mayall, apparently,
never saw the microscope which he described), I shall here
attempt to revise his version with the help of a few drawings
of my own. My account is based on personal examination of
three genuine specimens, one copy, and a study of all other
available data. I must point out, however, that my own
figures (Plate XXXI) were not drawn from any actual
instrument. They form a composite design—a generalized
2 ___ aa
all its references to L. (see Nachet, 1929). I have not seen the instrument in
this collection; but from the description and picture it appears suspiciously
like one of the recent copies of the Utrecht example.
1 Of. Disney (1928), p.160. This instrument is evidently a copy of
the original now in the Zoological Institute at Utrecht, and most of the
other copies appear to have been made from the same example. One such
has been figured recently by Becking (1924).
2 See the Catalogue of this sale, Lot 1.
* Woodcuts, made directly from photographs. These excellent figures
have recently been reproduced (as line blocks) by Disney et al. (1928,
Plate 1) without acknowledgement.
328 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”
representation of ‘“‘a Leeuwenhoek microscope ’"—embodying
all the features common to the extant examples. I have
tried to show the mechanism as simply as possible and with
the fewest and most easily comprehensible drawings, because
I find all previous accounts incomplete, inaccurate, or difficult
to understand. Several describers, indeed, do not themselves
appear to have grasped the mechanism—either literally or
metaphorically. My drawings are based primarily on the
microscopes formerly in the possession of Mr P. A. Haaxman
(The Hague), whose daughter—Mejuffrouw S. A. E. Haaxman—
very kindly permitted me (on 29 June 1923) to take one of
these priceless little instruments to pieces, sketch the various
parts, and reassemble it. For the accuracy of my description
I rely chiefly upon the notes and tracings which I made on
this occasion. Unfortunately I have had no opportunity of
testing any of Leeuwenhoek’s lenses.
All Leeuwenhoek’s microscopes had an appearance like
that shown in Plate XXXI, fig. 1. Properly speaking, they
were not “microscopes” at all, but—as he himself usually
called them—simple “ magnifying-glasses”. Hach consisted
of a single biconvex lens (not a system of lenses); and the
mechanical parts were contrived not to focus this lens upon
an object lying on a fixed stage (as in a modern compound
microscope), but in order to bring a movable object into the
focus of the glass, which was itself fixed. It is important to
realize this fundamental point in the design, which is highly
original. It should also be emphasized that all these instru-
ments were very small—even smaller than my drawings.
They were generally made of the same metal throughout,
though different metals were used (brass, copper, silver, and
even gold occasionally): and the workmanship and finish
were none too good. Leeuwenhoek concentrated his attention
upon the optical part of his “microscopes” : and when he had
succeeded in grinding and polishing and mounting a good lens,
he evidently did not think it worth while to spend a lot of
time in finishing off its mechanical accessories, which were
made just.good enough for his purpose.
Fig. 1 (Plate XX XI) shows the whole instrument from the
back, as fitted up ready for use. Figs. 2 and 3 illustrate details ;
and ‘fig. 4 is a diagrammatic longitudinal section. These
drawings will, I hope, almost explain themselves— if carey
studied ; but I may add the following notes :
PLATE XXXI
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LEEUWENHOEK’S © MICROSCOPE ”’
For explanation see the text.
facing p. 328
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LEEUWENHOEK’S MICROSCOPES 329
The minute biconvex lens (J, fig. 4) was mounted between
two thin oblong plates of brass (or other metal). Towards
one end of each plate, at the same point in the middle line, a
concavity was ground or punched and a hole pierced in its
centre. When these apertures had been made to coincide
exactly, the lens was clamped between the plates, in the
concavities (as shown in fig. 4), and secured by four equidistant
rivets forming the corners of a square (see fig. 1) with the lens
at its centre. In other words, the rivets and the lens—in
surface view—formed a quincunx, the lens occupying the
central spot.
The two oblong metal plates’ with the lens thus mounted
between them constitute the essential optical part of the
instrument. Leeuwenhoek probably kept many of his lenses
so mounted, and fixed interchangeable mechanical parts to
them as required. These mechanical accessories— for focussing
the object before the lens-—are shown in the figures and have
been well described by Mayall in his Cantor Lectures (1886)
as follows: ‘“‘ The object is held in front of the lens, on the
point of a short rod, the other end of which screws into a
small block or stage of brass [whose peculiar shape is shown
from above in fig. 2], which is rivetted somewhat loosely on
the smoothed cylindrical end of a long coarse-threaded screw
[figs. 1, 4] acting through a socket angle-piece | fig. 3] attached
behind the lower end of the plates by a small thumb-screw
[s, fig. 4. Only the projecting end of this screw is visible
in fig. 1. It is furnished with a roughly-fashioned metal
washer above the angle-piece—shown in section in fig. 4].
The long screw serves to adjust the object under the lens in a
vertical direction, whilst the pivoting of the angle-piece [fig. 3]
on its thumb-screw [fig. 4, s] gives lateral motion. ‘The
object-carrier can be turned on its axis, as required, by
screwing the rod into the stage [by means of a metal knob,
shown in figs. 1 and 4. When the rod is rotated by moving
the knob, the object is not only turned on its axis but raised
or lowered by the screw passing through the block—thus
forming a sort of “fine adjustment” for the “coarse adjust-
ment” provided by the long screw]. For focussing, a thumb-
1 The brass lens-holding plates of the best Haaxman specimen measure
approximately 41 mm. by 18 mm.; but their sides are not accurately
parallel, and their corners are roughly rounded.
330 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS”
screw passes through the stage near one end [figs. 1, 2,4], and
presses vertically against the plates, causing the stage to tilt
up at that end; the fitting of the long screw-carrier (angle-
piece [fig. 3]) is such that the stage at the end is sprung
down somewhat forcibly on the brass plates, and it is against
this pressure that the focussing screw acts.”
As we have already heard, the object to be viewed was
either stuck directly on to the pin of the object-carrier, or
else it was first mounted in some way (¢.g.,on a small plate of
glass or mica, or between two thin glass plates like a modern
slide and coverslip, or in a capillary glass tube) and the whole
was then fixed and focussed before the lens. A “ microscope”
of this type, with a lens of very short focus and high magni-
fication, must have been extremely awkward to manipulate.
It would be necessary to place the eye almost in contact with
the lens, and it is not clear how Leeuwenhoek was able to
obtain the requisite illumination. The known magnifying
power of his best glasses was, of course, sufficient to enlarge
objects as small as blood-corpuscles (and even bacteria) to
visually perceptible dimensions—a fact which modern workers
with the compound microscope seem apt to overlook. With
the front lens of my 2 mm. apochromatic objective—having a
magnification of about 120 diameters—I can distinctly see
(using the light of a clear sky only) bacteria as small as
Bacillus coli in a stained film. But to see such organisms
alive in water, and with sufficient clarity to describe their
movements, is another matter. (My own eyesight, I should
note, is exceptionally good—probably but little inferior to
Leeuwenhoek’s.) Yet Leeuwenhoek not only knew how to
make lenses of adequate magnifying power and aperture and
resolution, and sufficiently free from spherical and chromatic
aberration, but he also understood how to obtain the necessary
visibility. He was able,in some way, to get the indispensable
contrast between the object and its background which we
now readily obtain by means of central stops, iris diaphragms,
or staining.
It appears to me certain, indeed, that Leeuwenhoek cannot |
have made his extraordinarily accurate observations on bac-
teria and protozoa by means of the apparatus just described
when used in the ordinary way. He had unbounded patience
and magnificent eyesight—as his works abundantly testify—
LEEUWENHOEK’S MICROSCOPES 331
but he could not perform miracles. Moreover, there is no
reason to suppose that he possessed any apparatus essentially
different from that which is now known. (Blanchard’s sug-
gestion (1868) that he destroyed his best instruments in his
old age “with the idea of continuing to appear to everybody
as an incomparable observer ”’, is. quite unjustifiable.) All the
evidence indicates that it was the method of using this appar-
atus which he ‘“‘ kept for himself alone’”’: his secret lay, as he
tells us repeatedly, in his “ particular method of observing.”
What can it have been? The answer is—to me—almost
certain, though I cannot prove from his own words (since he
tried not to give his secret away) that I am right. I am
convinced that Leeuwenhoek had, in the course of his experi-
ments, hit upon some simple method of dark-ground wllwmin-
ation. He was well aware, as we know, of the ordinary
properties of lenses; and he tells us himself that he used
concave magnifying mirrors and employed artificial sources
of illumination (e.g. a candle). Consequently, he may well
have discovered by accident—or even have purposely devised
—some method which gave him a clear dark-ground image.
Such a discovery—possibly inspired by observing the motes.
in a sunbeam—would at once explain all his otherwise inex-
plicable observations, without supposing him to have possessed
any apparatus other than that which we now know he had.
But no hint was ever knowingly given, in all his many letters
(so far as I have been able to ascertain), of what his “ par-
ticular method of observing” may really have been.
Nevertheless, there is, in a very early letter, a remark
which seems to me to substantiate my interpretation—though
one must, I think, be personally familiar with such things to
appreciate it properly. Writing about red blood-corpuscles in
1675, Leeuwenhoek (in reply to criticism) says :*
. . . but I can demonstrate to myself the globules [= cor-
puscles] in the blood as, sharp -and clean as one can
distinguish with one’s eyes, without any help of glasses,
sandgrains that one might bestrew upon a piece of black
taffety silk.
1 From Letter’ 9. 22 January 1675. To Oldenburg. MS.Roy.Soe.
Unpublished.
* The words I have here interpreted and italicized are, in the original,
“desantgens . . . diemen op een swart sijde taff ‘soude mogen werpen”’.
332 LEEUWENHOEK AND HIs “ LITTLE ANIMALS ”’
Taffeta (formerly taffety or taffata—a word of Persian
origin) is a name now applied to various coloured fabrics of
wavy lustre: but in earlier times it denoted a silken cloth of
uniform texture—when black, much used for mourning. It
should be remembered that Leeuwenhoek speaks here not
only as a microscopist but also as a draper; and he therefore
meant that he could see human red blood-corpuscles under his
microscope just as clearly as he could see sandgrains scattered
on a piece of the smooth black silk he sold in his shop. The
more I consider these words, the more am I convinced that
nobody could ever have thought of such a simile unless he
had seen red corpuscles under dark-ground illumination.
Their appearance by transmitted light is wholly different, and
could never suggest such a comparison. To my mind these
words furnish an almost conclusive proof that Leeuwenhoek’s
“particular method of observing very small objects” was
some simple system of dark-field lighting, used in combination
with his ordinary microscopes. It is idle to speculate on how
he may have achieved this result : it is sufficient to note that
such a supposition will easily explain all his otherwise inex-
plicable observations. (It readily explains, for instance, how
he was able to see flagella and cilia and spirochaetes and
micrococci with a magnification of only some 200-300 dia-
meters.) But as he himself would say, “I hand this notion
over to others.”
Leeuwenhoek’s apparatus for viewing the circulation in
the tail of an eel was fully described and illustrated by
himself.’ It is a peculiar instrument, designed for a special
purpose, and not his “‘ microscope”? proper—though it has
more than once been figured as such by later writers. I need
not consider it here. I may note, however, that one of these
instruments is now in the Leyden Museum (with some lenses
made and mounted for it by himself, and a copy by another
maker). Leeuwenhoek’s own figures” show that he sometimes
used the lenses of his “ microscopes’”—mounted between two
oblong metal plates, as already described—in fitting up this
1 Letter 66. 12 January 1689. To the Royal Society. Printed in Dutch
and Latin works, but not in Phil. Trans. The original is preserved among
the Boyle MSS. of the Royal Society.
* See especially fig. 8, on the plate accompanying this letter.
LEEUWENHOEK’S MICROMETRY 333
apparatus. His magnifying-glasses were evidently so designed
that they could be used interchangeably for ‘ microscopes ”
or ‘‘enchelyscopes”’, as occasion required, by adding the
appropriate mechanical parts.
I may also note here that Leeuwenhoek was one of the
first—if not the very first—to study the structure of solid
opaque bodies by means of sections. Some which he cut
with his own hand “by means of a sharp shaving razor ” are
still in existence. They were enclosed in a little packet
affixed to an early letter,’ and have remained intact to the
present day. According to his own description, they are
(1) “Cork”; (2) ‘‘ White of a writing pen” [parings from a
quill] ; (3) “ Bits of the optic nerve of a cow, cut crosswise ”’ ;
(4) “ Pith of elder.” He added the following suggestions for
looking at these objects :
: I would venture to recommend that, when one
of these sections has been brought upon the pin of a
microscope, you then hold the microscope towards the
open sky, within doors, and out of the sunshine, as though
you had a telescope and were trying to look at the stars in
the sky through it.
LEEUWENHOEK’S MicroMEtRY.—Before the invention of
micrometers it was extremely difficult to measure very small
objects under the microscope: their size could, indeed, be
only estimated, by reference to other objects of known dimen-
sions. On an earlier page” we have read Leeuwenhoek’s
own account of the way in which he assessed the probable
magnitude of various animalcules, but a few further notes are
necessary.
Leeuwenhoek took the inch_(of his land and period) as an
absolute unit for small measurements. A copper rule,’ with
1 Letter 4. 1 June 1674. To Oldenburg. MS.Roy.Soc. Partly published
in English in Phil. Trans. (1674), Vol. IX, No. 106, p.121. L. also sent a
copy of this letter to Const. Huygens, and this copy—now in the Leyden
library—has recently been printed in its original Dutch by Vandevelde and
van Seters (1925).
* See p. 201 seq., supra.
3 Referred to on p. 189 supra.
334 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
the inches subdivided into tenths, was his standard. Fortu-
nately, he had this engraved for one of his later letters,’ so
that it can now be measured. From the picture it appears
that his “ inch’”’ was approximately 26°15 mm., and therefore
slightly greater than the modern English inch (25'4 mm.).”
His own drawing of a cubic inch (p. 189 supra) confirms
this determination.
The commonest objects with which Leeuwenhoek com-
pares ‘“‘animalcules” are a sandgrain, a human red_blood-
corpuscle, a vinegar-eel, and a millet seed. He also used
other more or less verifiable measures, however, such as “a
hairsbreadth,” “‘the diameter of a louse’s eye,” “the bigness
of a hair on a louse,” etc. J may say a word on each of these.
Sandgrains are Leeuwenhoek’s common standard of com-
parison. At first sight it seems impossible to translate these
highly variable structures * into exact modern measurements,
but it is actually—from the information which he supplies—
quite feasible. He generally referred to two kinds of sand—
coarse and fine. A fine sandgrain, according to the letter
translated on p. 188, was about #5 inch in diameter : but else-
where‘ he states that 100 of his very small sandgrains, laid
end to end, equalled about an inch. This seems to be the
usual magnitude he had in mind—7.e., about 745 of an inch,
or (using his scale) approximately 2604. A coarse sandgrain,
according to his own statement,’ was about 35 inch in
1 Send-brief XXVIII, to Boerhaave. 28 September 1716. Also published
in Latinin Epist. Physiol. and Op. Omn. The plate faces p. 271 of the Dutch
edition, and p. 266 of the Latin.
2 The scale in the figure is 5 inches long, and is accurately delineated.
A fair average can therefore be readily obtained for 1 inch. But as the
actual engraving was made on copper, and the prints are on paper (which
was wetted, and then shrank somewhat), I have made my estimate from
4 different prints in my possession (which differ only very slightly from one
another). The mean for 1 inch (here given) is therefore derived from the
combined measurements of 20 printed inches.
3 Ty. said himself (Send-brief XLI, 26 Aug. 1717) that “as big as a grain
of sand” is an inaccurate expression, andit would be better to use a millet
seed or a mustard seed for comparison.
4 Letter 35, to R. Hooke. 3 March 1682. Published in Dutch and
Latin works.
> Letter 42, to the Royal Society. 25 July 1684. Published in Dutch
and Latin works.
LEEUWENHOEK’S MICROMETRY 335
diameter, and therefore some 870 ». These magnitudes seem
to agree well with all Leeuwenhoek’s inferences—so far as
I have been able to check them.
A Red Blood-corpuscle (of man) measures about 7°5 u
in diameter, and Leeuwenhoek’s frequent choice of this
structure as a standard of size has been amply confirmed by
all later microscopists. Even today we commonly see an
outline of a human erythrocyte inserted among drawings
of microscopic organisms as an indication of their relative
magnitude.
It may be remarked here that Leeuwenhoek himself had a
very good idea of the actual diameter of a red corpuscle, though
he could not express it exactly in terms of any micrometric
unit : for he notes in one place’ that he had satisfied himself
that 100 diameters of a red corpuscle amounted to something
less than that of a coarse grain of sand (which he had just
assessed at 35 inch). Consequently, he imagined the diameter
of a corpuscle to be rather less than 3500 of an inch—an~
astonishingly good estimate.”
The Vinegar-Hel (the nematode Anguillula aceti) is
assigned various sizes in the text-books. I have cultivated
and studied this worm at various times, and find that ordinary
large individuals (females) may measure anything from about
1200 to 1700 in length. “A full-grown eel such as we
see in vinegar’”’ is approximately 1°51um. long, and this agrees
quite well with all Leeuwenhoek’s references.
A Millet Seed is more difficult to appraise. There are
now many kinds of millet (Panicum miliaceum)—*a name
applied with little definiteness to a considerable number of
often very variable species of cereals, belonging to distinct
genera and even subfamilies of Gramineae”’.* I have measured
1 Letter 42, p. 32 of Dutch edition.
* This was pointed out by Harting in 1850 (Het Mikroskoop, III, 404),
and again by myself (1920)—in ignorance of his earlier annotation.
Haaxman (1875, p.56) makes the absurd mistake of commending L. for
estimating the diameter at so (instead of goo) of an inch.
3 Encyclopaedia Britannica, 11th ed. (1911). It is rather surprising that
“a, millet seed” is still so frequently referred to, as a standard of size, in
biological writings (especially text-books). I have asked many people how
big a millet seed is, but have never yet found anybody who could tell me
even approximately—including one distinguished person who had himself
used the expression as a descriptive term.
336 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
samples of modern “ brown” and “ white ” millet (commonly
sold for bird-seed) and found that the grains averaged 1°8 mm.
and 2:17 mm. respectively: but as they are not spherical,
their “diameter” is difficult to determine. In one place’
Leeuwenhoek estimates a green pea to have a diameter equal
to 4} millet seeds, while elsewhere” he says that a pea weighs
8 grains. On selecting a few fresh green peas of about this
weight (520 mg.) and measuring them, I found their diameters
‘to be rather less than lem. (But here again—as peas are
not round—it is impossible to express their diameter, or
“axis”? as he called it, with precision.) If Leeuwenhoek’s
millet had a diameter of about # of such peas, it must have
measured roughly 2mm. across. This agrees with my
estimates from modern millet, and does not seem to disagree
with any of his own statements. I assume, therefore, that
when he uses “a millet seed” as his standard, he means a
spherical body approximately 2 nm. in diameter.
A Hairsbreadth is estimated by Leeuwenhoek himself? as
equal to g3o of an inch (about 43°6 w on his scale). The hairs
measured were plucked from his wig—not his own head—and
human hairs are usually much coarser.”
The Eye of a Louse’ appears to be rather an indefinite
standard of size. I find, however, that it can be estimated
approximately. The eyes of Pediculus humanus corporis (the
louse which Leeuwenhoek particularly studied) have fairly
uniform dimensions in both sexes. They are not spherical;
but series of measurements made longitudinally and trans-
versely give closely similar mean diameters. The average for
‘an eye of a big louse’’ I have found to be about 70 u—ranging
from 64 » to 80 w. It can thus be said, with a fair approxima-
tion to the truth, that ‘‘a louse’s eye’ has a diameter 10 times
that of a human red blood-corpuscle. This is in good agree-
ment with Leeuwenhoek’s interpretations.
1 See p. 169 supra.
> See p. 214 supra.
3 See p. 189 supra.
+ Most of my own hairs, which are unusually fine, have diameters at
least twice as great. I have never seen a human hair (from the head)
measuring only 43 u in diameter; but I have made no extensive investigation
of this matter—being content with L.’s own statement.
> Of. p. 121 et alibi, supra.
LEEUWENHOEK’S MICROMETRY RB
A Hair on a Louse is a less accurate comparison: for the
setae on P. corporis vary greatly in diameter, in different parts
of the body. Moreover, they all taper to a point, so that their
sides are not parallel. Large hairs, I find, have a maximum
width of about 4 »: but smaller ones measure only 2°5 w or
even less. “The thickness of the hairs wherewith the body
of a louse is beset” I estimate—very roughly—to be something
more than 3 yp.
I can add little else to what Leeuwenhoek himself tells us
about his micrometry.' I may mention in conclusion, how-
ever, that he had some correspondence on the subject with
Dr James Jurin in the last year of his life. Jurin, in 1718,
invented” a new method of measuring small objects ; and in
1722 he wrote to Leeuwenhoek about it, and persuaded him
to try it. Leeuwenhoek did so, and his answering letter was
published.’ Though it is not generally known, Jurin’s own
draft (in English) of his letter to Leeuwenhoek is still extant.
It is an interesting letter, and its present owner* has kindly
allowed me to read and copy it: but asit has no bearing upon
Leeuwenhoek’s own methods, I need not print it here.
Finally, I may note that the we:ghts mentioned by
Leeuwenhoek, in various letters, sometimes furnish clues to
his measurements. We could, indeed, exactly determine some
of his small measures of length if we knew the exact equivalents
of his weights in modern units. We do not know, however,
how closely his “grain” or “ounce” agree with modern
weights of the same name; though fortunately he recorded his
1 Tt should be noted that an earlier attempt to evaluate L.’s measure-
ments was made by Muys (1741; p.332, note 72). His words are worth
consideration ; but his estimates can hardly be regarded as satisfactory at
the present time, so I shall not discuss them here.
2 See Jurin (1718). His method was simple and ingenious. It consisted
in closely winding fine hairs or silver wire on a needle, along a measurable
length, and then determining the diameter of the hair (or wire) by counting
the number of turns in that length. The diameter of the filament being
thus ascertained, it was cut into small bits and strewn among the objects to
be measured, whose size was estimated (under the microscope) by comparison.
In this way Jurin determined the diameter of a human red blood-corpuscle
to be gz'z5 inch (a very close approximation).
3 Phil. Trans. (1723), Vol. XXXII, No. 377, p.341 (MS.Roy.Soc.
19 March 1723).
4 Mr A. K. Totton, a kinsman of Jurin and a former pupil of mine.
22,
338 LEEUWENHOEK AND HIS “LITTLE ANIMALS ”’
own “table of weights ” himself, so that we know their relative
values. Writing to Tschirnhausen * in 1699 he says:°
Over here we divide a pound |pont] into 16 ounces
[oncen], and each ounce into 20 engels,* and each engels
into 32 grains [asen]; and consequently, then, a grain
[aas] is todz0 Of a pound.
Tt is thus clear that Leeuwenhoek’s “grain” (aas), which
was gto of his ounce, can hardly have been identical with our
modern grain (4373 = 1 ounce, or 7,000 = 1 Ib. avoirdupois).
Wherever I translate “asen” as “ grains”, in the foregoing
pages, it is merely for want of any other term ; and the reader
will therefore please bear in mind that Leeuwenhoek’s * grain ”
was only approximately the weight nowadays called by the
same name in English (1 grain=0°065 gramme). But these
are problems for the expert metrologist—not for a poor
protozoologist or bacteriologist—and their further discussion
is beyond my competence.
(iv) LEEUWENHOEK’S DWELLING
The tragicomical history of Leeuwenhoek’s house in Delft
has never yet been fully related, but it deserves notice here
for several reasons. ‘These are the facts, so far as I have been
able to ascertain them. My information is derived chiefly
from Soutendam (1875), Haaxman (1875), Harting (1876),
Bouricius (1924, 1925), and an anonymous article” recently
published in the Wereldkroniek—supplemented by a few
personal observations and inquiries made on the spot in 1923.
In September 1875 an international celebration of “the
200th Anniversary” of Leeuwenhoek’s discovery of the
“Infusoria’”’ was held at Delft. (Harting [1876] records the
events which led up to this congress.) The fixing of the date
of the original discovery on September 1675 was, as we now
1. W. von Tschirnhausen (1651-1708), the well-known German
mathematician.
2 Letter 120, dated“. . . 1699.” Published in Dutch and Latin
collective works. See p.131 of Dutch edition.
* There is no English equivalent of this word.
4 See Anonymus (1909).
LEEUWENHOEK’S DWELLING 339
know, incorrect: nevertheless, the “ anniversary”? was duly
celebrated on the date erroneously determined—to the evident
satisfaction of all participants. By that time everyone had
forgotten where Leeuwenhoek had lived: but the then
archivist of Delft (Mr J. Soutendam) endeavoured to find
out, and he finally pitched on an old house standing at
the corner of Oude Delft and the Boterbrugstraat (not
‘“ Botersteeg”’, as Haaxman called it). An “ astrolabiwm” or
“planetarium” still present by the doorstep (figured by
Soutendam, 1875) was taken to confirm his identification of
the site—this bit of “scientific apparatus” presumably indi-
cating that the house in question had once been occupied by
a man of science. Even at that date (1875), however, the
house itself was, by all accounts, much restored and altered.
As Leeuwenhoek’s habitation had been thus identified, the
“anniversary ’’ celebrations included a visit of the delegates
en masse to this hallowed spot. The tenant of the house at
that time (Mr J. B. A. Muré) received them graciously: he
also allowed a stone memorial slab to be affixed to the front
of his residence, and bound himself legally to be responsible
for its future preservation. (The agreement is printed in
Harting, 1876; p. 89.)
So far so good. Some years later, however, the tenant of
the house died, and it passed into the hands of a builder at
The Hague who inconsiderately ordered it to be demolished.
By that date (1892) everybody had, apparently, forgotten all
about Leeuwenhoek again: but when the house came to be
pulled down, the stone block bearing his name, and the
‘‘ planetarium ” by the steps, were noticed. They were there-
fore preserved, consecrated with the seal of the municipality,
and deposited (on 3 December 1892) in the Municipal Museum
at Delft—where they now repose. (The memorial tablet is
an oblong block of white marble bearing the words Antony
vAN LEEUWENHOEK/MDCLXXV—MDCCCLXXV in gilt
capitals. The “planetarium” is a decorative iron railing
bearing no obvious resemblance to any scientific instrument.)
The site occupied by the house was not built on, but was
converted into a playground for the girls’ school adjoining
(the Meisjeshuis, erected in 1760); and again everything was
forgotten.
Some 17 years later, a local society called “ Delfia”—
concerned with the improvement of the town, and the preser-
340 LEEUWENHOEK AND HIS “LITTLE ANIMALS”
vation of its antiquities—realized that something ought to be
done to commemorate Leeuwenhoek in the place of his birth,
residence, and death. They therefore instituted a competition
in which artists were invited to submit designs for a suitable
memorial. ‘The winning entry was duly accepted and erected
—a bronze shield,’ showing a bas-relief bust of Leeuwenhoek
(modelled on Verkolje’s portrait) with a Dutch inscription,
executed and signed by J.C. Schultsz. It is still stuck on the
railings surrounding the school playground, where it was
affixed in 1909. Apart from his tomb, this is still the only
monument to Leeuwenhoek in Delft.
But more recent research into the town archives—made
by a later and more critical archivist, the late Mr L. G. N.
Bouricius—has proved that Leeuwenhoek never lived on the
spot where his modern bronze effigy with its false inscription
now hangs. His real residence was in a neighbouring street
—the Hippolytusbuurt—and has long since vanished without
trace. Consequently, all the belated local endeavours to
commemorate Leeuwenhoek have been futile. It is certain
that he never lived on the spot where the delegates were
thrilled in 1875, and where his memorial now incongruously
stands: nor did he make the supposed discoveries in the year
therein alleged. His own house—where he lived and laboured
and died—was in a different street, and has long since been
destroyed by his forgetful fellow-townsmen. ‘The railings
adorning another man’s doorstep—now preserved in the
Municipal Museum of Delft—are a worthless object which
would surely have excited his derision.
Before the celebrations of 1875 were held in Delft, invita-
tions were issued by the organizing committee to every body
and everybody likely to be interested. Yet England—almost
alone—made no response. The Royal Society, indeed, not
only sent no delegate, but even failed to acknowledge their
invitation: and England and London and the Royal Society
thus placed themselves—to quote Harting (1876)—“on a
level with Spain and Portugal and Greece.” We ought,
undoubtedly, to have taken some part in commemorating
Leeuwenhoek’s discoveries, with which we were so intimately
concerned: yet our disgrace is now, perhaps, mitigated by
1 Figured in the anonymous article in the Wereldkroniek (1909). A
plaster cast is also preserved in the Museum at Delft.
LEEUWENHOEK’S DWELLING 341
the accidental circumstance that no Englishman or Fellow of
the Royal Society was present at the farce enacted in 1875 at
‘* Leeuwenhoek’s house, where he discovered the Infusoria in
1675”. But the whole affair is deplorable, and the less said
about it the better.
The comedy of errors associated with ‘ Leeuwenhoek’s
house ” is unhappily paralleled in the history of his birthplace.
About ten years ago, Mr Bouricius succeeded in discovering
the place where Leeuwenhoek was born—a house in the
Oosteinde of Delft, at that date still erect but used as a
warehouse by a hide-merchant named Roes. Bouricius (1925)
published a picture of this building, and with his kind assist-
ance I had it rephotographed in 1926. (See Plate II.’) But
in February, 1929, Mr Bouricius unfortunately died: and
later in the same year, when Dr Schierbeek was about to
propose to a Dutch scientific gathering’ that a commemora-
tive tablet should be placed on the house, he found that it
had just been pulled down—to enlarge the playground of
another children’s school !
It will thus be seen that the house in which Leeuwenhoek
was born, the other house in which he lived and worked
and traded and died, and even the house in which he is
now erroneously supposed to have resided, have all been
demolished. Delft, Holland, England, London, the Royal
Society, and everyone else in every land, may therefore all be
censured for having done nothing to preserve Leeuwenhoek’s
bodily connexion with the world.
But it is needless to bewail the hard fact that such
material relics of Leeuwenhoek’s existence have been thus
wantonly destroyed. His own works are a monumentum aere
perennius which no vandal or house-breaker or Fellow of the
Royal Society can ever annihilate. For my own part, I feel
no sorrow when I reflect that the site of his own dwelling
is now occupied by an obscure modern shop: and I almost
rejoice that the place where he was born, and the ground
1 This photograph has already been published, unfortunately, by Dr
Schierbeek (1930), though it was taken at my expense for the present work.
I note this lest I be accused of borrowing his illustration without
acknowledgement.
2 Genootschap voor Geschiedenis der Genees-, Natuur- en Wiskunde.
“cc
342 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
whereon he is wrongly supposed to have lived, are both now
open spaces where little Dutch children can play in the sun.
I even find something appropriate, poetic, and comforting in
these ‘‘ inscrutable dispensations of Providence.”
(v) LEEUWENHOEK’S DRAUGHTSMEN
It is well known that most of the illustrations accompanying
Leeuwenhoek’s letters were not drawn by his own hand. He
tells us himself that he was a poor draughtsman, and therefore
employed more skilful artists to make his figures.’ There are
several references to this subject in his published works ; but
perhaps the most explicit expression is to be found in an early
unpublished letter, wherein he says—in answer to Oldenburg’s
complaint that his drawings were not sufficiently clear—that
he sees with the utmost clarity all that he describes, but then
adds :°
Yet I am to blame, because I can’t draw; and secondly,
because I am resolved not to let anybody know the
method that I use* for this purpose: and so I just make
only rough and simple sketches with lines, mostly in
order to assist my memory, so that when I see them I
get a general idea of the shapes: besides, some of the
forms I see are so fine and small, that I don’t know how
even a good draughtsman could trace them, unless he
made them bigger.
Many of the original drawings sent with the letters to the
Royal Society have been preserved. They are, for the most
part, of no great artistic merit, and differ in minor details
from the published engravings. This is, in the main, because
the originals were usually drawn with red or black chalk, or
pencil (exceptionally with ink or in colour), and were often
reduced in size by the engraver. All variations are readily
explicable by the difference in technique—the soft line made
with red crayon on paper being impossible to render exactly
by the hard line of the burin on metal. On the whole, the
1 Cf. Letter 2, p. 42 supra.
2 Translated from Letter 11. 26 March 1675. To Oldenburg. MS.Roy.Soc.
* je, in handling the microscope—as is evident from the context.
LEEUWENHOEK’S DRAUGHTSMEN 343
engravers dealt faithfully with their prototypes: and I
fancy that the average modern editor, if drawings such as
Leeuwenhoek’s originals were submitted to him in illustration
of a present-day paper, would return them to the author with
a note saying that they were “not suitable for reproduction”.
I have, indeed, been compelled to act on this principle myself :
the original drawings, en sanguine on discoloured and yellowish
paper, illustrating the letters on Anthophysa and the protozoa
on duckweed, are still extant; but I cannot reproduce them
here—for technical reasons—and have had to use the
engravings originally made from these drawings instead.
A few “rough and simple sketches ’’—mostly on the mar-
gins of the MSS.—were evidently the work of Leeuwenhoek
himself’: because careful examination shows that they
were drawn with the same pen and the same ink as the
accompanying autograph handwriting. They bear out his
own statement that he was no artist.
In Leeuwenhoek’s letters I have been unable to find any
mention of the name of the draughtsman—“‘de teijckenaer’’, or
“the limner’”’ as Hoole always calls him—who made his
illustrations for him. (He is frequently mentioned, but never
by name.) It is unlikely, indeed, that all the drawings were
executed by the same artist, for they were made at intervals
during some 50 years; and there is no reason to believe that
Leeuwenhoek’s longevity was characteristic of all citizens of
Delft at that period. It seems to me certain, therefore, that
more than one hand must have participated in the illustration
of his discoveries.
It is generally supposed that Leeuwenhoek’s draughtsmen
are unknown. Nevertheless, there is at least one important
record bearing on this subject which seems to have been
overlooked. In Boitet’s book on Delft (1729; pp. 790-91) we
are told of a certain Thomas van der Wilt (born 1659”), who
was ‘‘a fine painter and a good poet,” and who was a pupil of
Johannes Verkolje. It is said by Boitet that he settled in
Delft, and there found plenty of work as a portrait-painter and
otherwise; and “ By his wife Johanna Biddaff he had a son,
1 The cube illustrating the argument in the letter to Const. Huygens
(p. 189 supra) is one as these: and the pepper-tube (Plate XXII) is
another.
* He died at Delft in 1733 (fide Bryan, 1905).
344 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
called Willem, who made such progress in drawing, through
his father’s instruction, that there were few who could match
him. Nearly all the plates in the celebrated work of Mr.
Leeuwenhoek were marvellously drawn from life by him
through magnifying-glasses. .... But hediedin the flower
of his life on 24 January 1727, at the age of 35.”
There is no reason to doubt the truth of this story—
published only two years after Willem’s death in his home
town: but it is impossible to believe that Willem van der Wilt
drew “nearly all” (meest alle) Leeuwenhoek’s figures. If he
died aged 35 in 1727, he must have been born in 1691 or 1692;
and consequently he could have drawn none of the illustrations
for the letters written in the XVII Century. He probably
made the illustrations of the Send-brieven: but he could not
have been responsible for any others—save some of those
reproduced between 1700 and 1712 in the Phil. Trans. The
pictures of vorticellids and rotifers published at the beginning
of the XVIII Century may perhaps have been drawn by hin,
and it may well have been Willem who made the recorded
remark about their surprising “ wheelwork”’’.* But he must
have been a mere child at the time.
Whilst there is thus good reason to believe that
Leeuwenhoek’s last letters were illustrated by Willem van
der Wilt, there seems to be no direct evidence to show who
drew the figures for the earlier ones. Nevertheless, it seems to
me probable that some of them may have been drawn by his
father Thomas. If we consider all the evidence furnished by
Boitet, it appears to me highly suggestive. Very briefly, it is
as follows: (1) Thomas van der Wilt was an artist living in
Delft at the time when Leeuwenhoek wrote his early letters.
(2) His son was employed by Leeuwenhoek to illustrate his
later letters. (3) Thomas himself must therefore have been
known to Leeuwenhoek.’ (4) He (Thomas) earned a good
living in Delft not only by painting portraits, but also by
exercising his artistic abilities in other ways. (5) Thomas’s
father, though not a native of Delft, was a linen-draper—the
trade which Leeuwenhoek himself engaged in. (6) Thomas
* Cf. p. 279 supra.
2 This is confirmed by the cireumstance—mentioned a little later—that
Thomas was responsible for some panegyric verses elucidating the allegorical
title-page of the Send-brieven.
LEEUWENHOEK’S DRAUGHTSMEN 345
was a pupil of Verkolje—the artist who painted Leeuwenhoek’s
portrait.
What could be more likely, therefore, than that
Leeuwenhoek employed Thomas van der Wilt to draw the
pictures for some of his earlier epistles? When all the
circumstances are taken into account, this seems to me to
be something more than a plausible guess at the identity of
one of the original draughtsmen.
But Leeuwenhoek must have known other artists who
lived in his native town, and the evidence in favour of Thomas
van der Wilt is clearly not conclusive. Among Leeuwenhoek’s
acquaintances we must include, for example, that incomparable
painter Jan Vermeer. He was born in the same year as
Leeuwenhoek, in the same place, and at almost the same
hour (their baptisms are registered on the same page), and
lived and worked all his life in Delft—of which he has left us
one of the most beautiful pictures in existence (see Plate VII).
Moreover, we know that, on Vermeer’s untimely death in
1675, Leeuwenhoek was appointed as his executor.’
I must note, in conclusion, that Thomas van der Wilt once
painted a portrait of the poet Hubert Poot (1689-1733), who
wrote Leeuwenhoek’s epitaph ; and an excellent engraving of
this picture, by Houbraken, was prefixed to Poot’s collected
Gedichten (Delft, 1722)—reproduced here in Plate XVI.
I have seen no other specimens of Thomas’s artistic work,
but according to Boitet and others he also painted the
Rev. Mr Gribius—Leeuwenhoek’s minister, who announced
his death to the Royal Society (see p. 93 supra). The only
sample of Thomas's poetry which I have seen is the poem
explaining the engraved title-page—‘ Op de Titel-prent’’—
of Leeuwenhoek’s Send-brieven (1718: not printed in the
Latin edition [Epist. Physiol.]|, 1719).
For my part, I accept Boitet’s evidence that Leeuwenhoek’s
later letters were illustrated by Willem van der Wilt, and
I incline to the view that some, at least, of the earlier ones
were illustrated by his father Thomas. But the subject
obviously demands further research, which I must leave to
future students possessed of the time and opportunities
requisite for pursuing inquiries of this character.
1 Vide p. 35 sq., supra. It is noteworthy also that L.’s microscopes
were ultimately auctioned in the chamber belonging to the artists’ Guild of
St. Luke—of which Vermeer was sometime “ Master ”’.
6e
346 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
(vi) THE PORTRAITS OF LEEUWENHOEK
Several “portraits of Leeuwenhoek” are still extant.
They were made at various dates by various artists, and the
following fragmentary notes upon them may be of interest—
information on this subject being somewhat difficult to obtain,
and not having been previously collected.’
(1) By JoHANNES VERKOLJE (1650-1693 : lived at Delft
1673 till his death, and is buried there. Cf. v. Riemsdijk,
1921, p. 281). There are two portraits of Leeuwenhoek by
this artist :
(a) An otl-painting. (See Plate XI, opposite p. 49 of
the present work.) Dated 1686 (fide Moes, 1905). Three-
quarter length, showing Leeuwenhoek seated at a table;
wearing a golden-brown robe, a wig, a knotted white necker-
chief, etc. Head turned to left of picture (7.e. to his own
right), knees to right. On the table a globe, an ink-stand
with a quill pen, the sealed diploma of the Royal Society, a
small pair of compasses, and a sheet of paper bearing a
drawing of acircle and some indistinct figures. (The drawing
appears to be that here shown in text-fig. 38, p. 202.) In
his right hand he holds another pair of compasses.” He
is depicted with a fresh complexion and clear blue eyes.
An opening at the right in the dark background shows
a glimpse of a distant landscape with a winding river
(“perhaps the Thames” according to Haaxman—but why
not the Maas?).
This painting was formerly in the possession of Dr C. H. W.
van Kaathoven of Leyden (Haaxman, 1875, p. 177: Harting,
1876, pp. 117-119). On his death it was purchased (19 June
1879) by the Rijksmuseum, Amsterdam, where it now hangs
(Room 273, No. 2521). Cf. Moes (1905, p. 12); v. Riemsdijk
(1921, p. 281). This isthe prototype of most of the published
portraits. It has been reproduced in recent times by
Crommelin (1926), van Seters (1926), and others, while
1 Since this was written a short article on the same subject has been
published by de Lint (1931)—too late for its contents to be discussed here.
2 A little passer similar to this, and once belonging to L., is still (or was
in 1923, when I saw it) in the possession of Mr P. A. Haaxman at The
Hague.
PORTRAITS OF LEEUWENHOEK 347
Haaxman had it lithographed'—by A. J. Wendel, not very
successfully—as a frontispiece for his biography (1875).
(b) A mezzotint engraving. (See the Frontispiece.) This
differs from the painting chiefly in the following particulars:
the head is turned to the right, knees to the left; and
Leeuwenhoek holds a microscope in his left hand (not com-
passes in his right). The whole picture is, in fact, reversed.
On the table, instead of the diploma, there is a spray of oak-
leaves with galls” on them, and a large magnifying-glass
with a handle. A curtain hangs behind the head, and the
distant landscape is missing. Below is engraved a Dutch
inscription with some verses signed “‘ Constanter ” (the pen-
name of Constantijn Huygens pater). The mezzotint is
signed “J. Verkolje pina. fec. et exc. A°. 1686.”* (This is
important, as it confirms the date of the painting.)
Several prints, at least, of this engraving are in existence.
Dr van Kaathoven, of Leyden, formerly possessed one, which
afterwards passed into the possession of Mr P. M. Beelaerts,
who in turn bequeathed it to the town of Delft." (It is now
in the Gemeentemusewm.) But the best impression which I
have seen is in the private collection of Mr George H. Gabb
(London), from whose copy my frontispiece has been repro-
duced. Other reproductions of the mezzotint (from other
originals) have previously been published in Opuscula Selecta
Neerlandicorum, Vol. I (1907); by Locy (1910, p. 79) and
Cole (1926, frontispiece); and in the Deutsche Medizinische
Wochenschrift (1911; No. 22, supplement). This last plate—
included in that journal’s ‘‘ Bildersammlung aus der Geschichte
der Medizin’’—is a fine large half-tone reproduction, but bears
1 This poor lithograph has unfortunately been copied (instead of the
equally accessible original) by several well-meaning popular writers—such
as Baumann (1915) in Holland, and Mrs Williams-Ellis (1929) in England.
2 Letter 50, 14 May 1686 (published in Dutch and Latin works) contains
a description of L.’s observations on oak-galls, and its date affords confirmation
of the date of the engraving.
3 Not 1685, as stated by Haaxman (1875, p. 187).
4 Of. Haaxman (1875) and Veldman (1898, p. 74). I have seen this
impression, which is fairly good.
* I am greatly indebted to Mr Gabb for his permission to copy the
original in his collection, and for the trouble which he has taken to insure
its accurate photographic reproduction.
348 LEEUWENHOEK AND HIS “ LITTLE ANIMALS ”’
a ridiculous biographical note (signed ‘“‘ Pagel’’) on its back.
The original picture is therein hesitatingly attributed to
“J. Veikolpe”’, and “Anton” van Leeuwenhoek is called a
‘well-known precursor of Robert Koch, in so far as the
discovery of the infusoria is due to him.”
It seems obvious that Verkolje first made his portrait of
Leeuwenhoek in oils, and shortly afterwards (in the same
year) himself engraved it in mezzotinto. The artist evidently
copied his own painting directly on to the copper plate (which
accounts for the figure being reversed in the printed engraving),
and in doing so made several minor alterations or improve-
ments—appropriately substituting a microscope for the
compasses originally held in the hand, but failing to notice
that he ultimately made Leeuwenhoek appear left-handed !
The mezzotint by Verkolje is probably the best of all portraits
of Leeuwenhoek: and that it was an excellent likeness is
attested by the verses written on it by Const. Huygens.
There are several references to this mezzotint by
Leeuwenhoek himself in unpublished passages in his letters.
Apparently the Royal Society wrote, about the beginning of
1694, to ask him for his portrait. In his reply he says: ’
I haven't any of my pictures; and furthermore, the
plate has been printed off, and the plate-maker, who was
also the printer and painter,” is dead. But if I can get
one at our approaching annual fair, at which time many
art-dealers come to our town, I’ll not neglect to let you
have what you ask for.
Later in the same year he wrote again: °
I couldn’t find any copies of my portrait, in mezzotinto,*
for sale by any of the printsellers at our annual fair: but
at last ’'ve gotten six copies from a bookseller in another
1 Translated from Letter of 26 May 1694. To R. Waller. MS.Roy.Soc.
Unpublished.
2 Referring to Verkolje, who died in the previous year.
3 From Letter 84. 14 September 1694. To R. Waller. MS.Roy.Soe.
Published in Dutch and Latin printed works, but with the passage here
translated entirely omitted. Not in Phil. Trans.
* inde swarte konst MS.
PORTRAITS OF LEEUWENHOEK 349
town, which I dispatched a fortnight ago to London by
Skipper Richart Houlatson, with the address: For the
Secretary of the Royall Society at Gresham Colledge,
without any further inscription.
The Royal Society failed to acknowledge the receipt of
these letters and pictures (and also of other letters from
Leeuwenhoek received at that time), and two years later we
find him writing again *:
When I learnt that several Fellows were wishful to
have two or three copies of my portrait, printed in
mezzotinto, . . . I couldn't remain idle, but made
every effort to satisfy them; and finally I obtained six
prints (as the plate had been printed off). These mezzo-
tintos, as also my Latin book, I sent to London, and
addressed them, as I’ve been wont to do, to Gresham
Colledge: to all which letters I got no answer
What happened to these six prints is not now known.
They have all disappeared from the Royal Society’s collection,
and the Society now possesses only a single mutilated copy of
the mezzotint acquired at a much later date.
All the well-known engraved portraits of Leeuwenhoek are
derived from Verkolje’s oil-painting. The best-known, and
most often reproduced, is the excellent copperplate engraving
by A. de Blois prefixed to the Dutch and Latin collective
works (Brieven and Opera Omnia). It first appeared as a
frontispiece to the Vervolg der Brieven (1687), with a Dutch
inscription: afterwards, with Latin lettering, in Arcana
Naturae Detecta (1695). Various copies of this copy have
also been made—in line, stipple, mezzotint, and by modern
photographic processes. At least one early engraving was
1 The words “For . . . Colledge” are thus in English in the MS.
(The rest, of course, is in Dutch.)
2 From Letter 102. 10 July 1696. To the Royal Society. MS.Roy.Soc.
Published—with omission of the passage here translated—in the Dutch
and Latin printed works: English extract in Phil. Trans. (1696), Vol. XIX,
No. 221, p. 269 (from which the passage isalso absent). This letter actually
contains a protest against the Society's failure to acknowledge 8 of L.’s
communications (Letters 77 to 84)—a discourtesy which caused him to
start sending his observations to other people instead.
350 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”
reproduced in colours. The best steel-engraving (copied from
de Blois) is that by A. Smith,’ prefixed to Hoole’s Select
Works (Vol. I, 1798): but another good one—probably copied
from Smith’s, but with the head turned to the right (as in the
original mezzotint)—was made by J. Chapman and published
by G. Jones in 1813. All these reproductions show
Leeuwenhoek’s head only, in an oval frame with more or
less added decoration.
Regarding Anker Smith’s engraving (in Hoole) the
following points should be noted. Although it bears an
extract from a Dutch letter printed in 1696, and is marked
“ Painted by I. Verkole”’, it was almost certainly copied from
the engraving by de Blois accompanying the Latin Arc. Nat.
Det. The oval frame bears the words: “ANTONIUS A
LEEUWENHOEK DELPHENSIS, R.8.8. AET. LXIII.
MDCXCV.” Both age and year are entirely wrong, and
consequently this circumscription has already led to mis-
understanding. JI can only suppose that Smith (or Hoole)
wrongly took the date of the Arc. Nat. Det. (1695) as that in
which de Blois’s engraving was made; and that the age of 63
was then inferred from this error. Anyway, there can be no
doubt that Smith’s engraving was ultimately derived from an
original made in 1686 (not 1695), which portrayed
Leeuwenhoek at the age of about 54 (not 63).
Verkolje’s portraits have been copied and recopied over
and over again, and terribly travestied and perverted in the
process. ‘The die of Leeuwenhoek’s own seal * was admirably
incised from the mezzotint: the modern bronze effigy’ of
himself, now suspended in Oude Delft, is also based—less
successfully—on Verkolje’s originals. Moreover, there are
contemporary tiles and pottery of Delft-ware bearing
Leeuwenhoek’s supposed simulacrum “ after Verkolje” (a very
long way after). I have seen two samples of these—a plate
and a plaque—now in the Riyksmuseum; and Haaxman and
Harting mention others. I have also seen a present-day
descendant of Verkolje’s pictures—showing “the man who
1 Anker Smith (1759-1819), a once celebrated engraver of small plates
for book-illustration. He was elected.A.R.A. in 1797.
2 Ct. p:. 360.
3 Cf. p. 340 supra.
PORTRAITS OF LEEUWENHOEK 351
first saw a microbe”—in an English children’s magazine,
and a comic reconstruction recently (1931) used to advertise
an American proprietary tooth-paste in India: but the last
stage in degradation has surely been reached in the caricature
imprinted on the covers of the current American Abstracts of
Bacteriology (Vol. I issued in 1917) and some other publications
of the Society of American Bacteriologists.
(2) By Nicotars Mass (1632-1693: from 1673 to 1693
at Amsterdam, where he died and was buried). According
to C. H. de Groot (1916: Vol. VI, pp. 530-531) there are
two portraits of Leeuwenhoek by Maes. The first (No. 202,
de G.) is an oil-painting now in the National Gallery, London
(1921 Catalogue, No. 2581). This picture was formerly owned
by Mr George Salting, the Australian art-collector, and was
bequeathed to the Nation in 1910. It is undated, and depicts
an old man “in full face. His right hand is raised, grasping
his robe. He has long hair, a moustache, and a pointed beard
on his wrinkled face. |He wears a black robe and a white
shirt.| At the back is a curtain, with a column in shadow to
the right’ (de Groot). This is a very fine painting, but it is
certainly no portrait of Leeuwenhoek. It shows a man totally
unlike the sitter for Verkolje’s portraits, and there is no
evidence whatsoever that it depicts our Antony. In 1923
I called the attention of the then Director of the National
Gallery (Sir Charles Holmes) to this misidentification: and on
looking into the matter for himself he agreed that ‘‘ there is
no just ground for identifying the portrait . . . as a portrait
of Leeuwenhoek.” He informed me further that the picture
was first labelled “ Anthony van Leeuwenhoek, F.R.S.” after
it left the Salting Collection—by whose authority is not now
known.” Its label has consequently now been changed to
“ Portrait of a Gentleman”. De Groot blundered badly when
he accepted this painting as a portrait of Leeuwenhoek.
According to de Groot there is also another portrait (like-
wise undated) by Maes. It is described as follows: ‘‘ 202a.
ANTHONI VAN LEEUWENHOEK.—In a dark red coat trimmed
with fur. His long hair falls on his shoulders. 28 inches by
24 inches. Sale.—Lady Anna Chandos-Pole and others,
1 See Anonymus (1927).
2 Letters dated 8 & 10 May 1923.
352 LEEUWENHOEK AND HIS ‘“ LITTLE ANIMALS ”
London, July 19, 1914. No. 106” (de Groot, 1916: Vol. VI,
p.531). Whether this is a genuine portrait or not I do not
know. I have been unable to trace it further. I can only
add that according to Art Prices Current, 1913-1914 (Vol. VI,
pp. 307, 505), the picture was not the property of Lady Chandos-
Pole, but belonged to Maj.-Gen. Sterling, of 249 Knightsbridge,
London, and was sold at Sotheby’s on 29 April 1914 for £46:
while later in the same year (10 July 1914—not 19 July, as
stated by de Groot) it is said* to have been resold at Christie’s
for £120. 15s.
Notwithstanding the allegations of de Groot and others,
there seems to be still no satisfactory evidence to prove that
any portrait of Leeuwenhoek was ever painted by Maes: but
the matter obviously needs further investigation.
(3) By ADRIAEN VAN OsTADE (1610-1685: born at Haarlem,
where he worked and died). See Moes (1905; Vol. IT, p. 12)
No. 4415 (1): de Groot (1910; Vol. IIT, p. 410) No. 876.—De
Groot calls this a “ Portrait of Anthonie van Leewwenhoek (1632-
1722), physicist and surgeon of Haarlem”’,” and he describes
the picture thus: “ He sits, turned three-quarters left, and
leans his left arm on the table and his right hand on his hip.
He wears a black costume with a white collar and brown
gloves. In front of him are a book and a celestial globe.
Signed in full at the foot of the globe, and dated 1665; panel,
81 inches by 7 inches.” This portrait is stated to have been
sold in Paris on 2 May 1865 (Sale H. de Kat, No. 63). Ihave
been unable to find it. I may note, however, that what
appears to be a copy in black chalk, by A. Delfos, is preserved
in the Municipal Museum at Delft. It is a poor portrait (if it
be one) and bears little resemblance to the authentic pictures
of Leeuwenhoek, though the face recalls many of the peasants
portrayed in Ostade’s other paintings.
Adriaen van Ostade was no portrait-painter (and in my
opinion a very poor artist): and at present I am not convinced
that he ever attempted to paint a portrait of Leeuwenhoek—
or, if he did, that it is now in existence.
1 Tt is also there said to represent ‘“‘ Lieuvenhoch, the father of the
Microscope”!
2 There are 5 obvious errors in these dozen words.
PORTRAITS OF LEEUWENHOEK 353
(4) By CoRNELIS DE MAN (1621-1706: born, worked, and
died at Delft). According to Moes (1905; Vol. II, p.12)
there is—or was—a portrait of Leeuwenhoek by this artist,
dated 1681, in the “ Anatomie-Kamer te Delft.” When I
visited the town in 1923 I was unfortunately unable to find it:
and subsequent inquiries made through the late archivist
(Mr Bouricius), and the late Prof. Beijerinck, have been
equally fruitless.
(5) By JAN VERMEER (1632-1675, of Delft). There is no
authentic record of any portrait of Leeuwenhoek having ever
been painted by this great master. Nevertheless, it has
recently been stated by Lucas (1922, p.8) that Leeuwenhoek,
“the inventor of the microscope,” was “ probably his model for
the three or four scientific pictures”. (By “scientific pic-
tures” Lucas means those paintings by Vermeer showing a
“Geographer” or “ Astronomer” at work.) I have not seen
the originals of any of these (nor had Lucas when he wrote),
but I have studied good photographic reproductions of them
all. ‘There are four, and they appear to me to portray as many
different people. No two are alike, and none bears any
recognizable likeness to Leeuwenhoek—as we know him from
Verkolje’s authentic portraits. I am entirely at a loss to
understand how anyone can seriously suggest that Vermeer’s
‘“Geographers”’ and “ Astronomers” all represent the same
person—and that person Leeuwenhoek. ‘The suggestion
becomes still more perplexing when we find that Lucas (op. cit.,
p.20) also accepts as genuine the spurious “portrait” by
Maes '—which in no way resembles any of the people depicted
by Vermeer or Verkolje.
I must call attention, however, to some curious points
which came to my notice whilst seeking evidence (not given
by him) for Lucas’s statements. The very fine painting by
Vermeer known as “ The Geographer,” now in the Stddelsches
Institut at Frankfort,’ shows a man poring over a map or
chart, and with a pair of compasses in his right hand. Behind
his head there is a globe, and some other maps are also in the
1 See above, p. 351.
* There is an excellent reproduction in colour in “Jan Vermeer of
Delft’ (Portfolios of Great Masters), published by Halton & Truscott
Smith, Ltd. London, 1925.
23
354 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
picture—a couple loose on the floor, one framed on the wall.
This is one of the few of Vermeer’s pictures which is signed
and dated. The date, painted on the wall behind, is
MDCLXVIIII (z.e., 1669—not 1668, as stated by more than
one writer on Vermeer). Now this is the very year in which
Leeuwenhoek was appointed surveyor." Moreover, the globe
in the picture is apparently a celestial (not terrestrial) globe,
and is very like that shown in both of Verkolje’s portraits.
Leeuwenhoek must surely have possessed a similar one. In
Verkolje’s oil-painting, furthermore, Leeuwenhoek is shown
holding a pair of compasses in his right hand *—just like
Vermeer’s “Geographer”. The framed map on the wall has
only an artistic import: it has no “ scientific” significance,
being simply a decoration—introduced into many of Vermeer’s
other pictures which have no connexion with geography.
There is no authority for calling this picture “The
Geographer ’”’—a modern label. Suppose we call it “The
Surveyor”? This title seems equally appropriate; and we
might then suppose that Vermeer was inspired to paint it by
seeing Leeuwenhoek at work on ground-plans and surveys in
preparation for his qualifying examination in 1669! But all
this is mere guesswork, though the coincidences Just noted are
curious—if nothing more. “The Geographer” himself is not
much like Leeuwenhoek; and there is no evidence, as I have
already remarked, that Vermeer ever painted his portrait.
(6) By JAN GOEREE (1670-1731: designer, engraver, and
poet. Known also as Gouré).—In the engraved title-page of
Leeuwenhoek’s last published letters (Send-brieven and Epist.
Physiol.) there is inset a little oval portrait circumscribed
“ANTONIVS LEEUWENHOEKIVS DELPHIS NATVS
MDCXXXII”’. It is supported by a fat female angel blowing
a trumpet, and somewhat overclouded by other allegorical
accessories. The first state of this plate (in the Dutch
edition) is lettered at foot “Te DELFT by ADRIAAN
BEMAN, 1718.” and in the left bottom corner “J. Goeree
sculpt: Direa.” The second state (Latin edition) bears the
words “DELPHIS apud ADRIANUM BEMAN, 1719.”
—with the same signature.
1 Cf. p. 34 supra.
* See Plate XI, facing p. 49.
PORTRAITS OF LEEUWENHOEK 355
I formerly attached but little importance to this small
detail—believing it to be on a level with the rest of the
engraved title. Buta few years ago Dr W. H. van Seters, of
Leyden, when collecting material for the ‘‘ Leeuwenhoek
Film ” (which has now been exhibited on various occasions :
cf. Kaiser, 1924), rediscovered’ an old design above which
Leeuwenhoek once wrote a motto and his name. Dr van
Seters kindly sent me a photograph of this drawing (included
in the film), which reveals several points of interest.
Leeuwenhock’s signature (undoubtedly genuine) is there dated
30 April 1698. It is written at the top of the page, and is
followed by a large allegorical drawing illustrating his motto f
(“ Door Arbeyt en Naarstigheijt””). But this drawing was
evidently added later, as it is signed “ J. Goeree del: 1707.”
Moreover, it bears, as a pendant, the miniature portrait of
Leeuwenhoek incorporated later in the engraved titles of his
last letters. This picture was therefore probably made in
1707—not at the date of publication of the Send-brieven
(1718). Careful study of the engraving has also convinced
me that it was made with considerable care, and under
Goeree’s own supervision—as the words “sculpt: Durex.”
sndicate. 1 therefore now regard this portrait (shown in my
Plate XII) as a genuine and conscientious attempt, by fairly
competent artists, to delineate Leeuwenhoek as he appeared
in his 75th year. In any case, this is the only known portrait
of him in his later life which can make any pretence to
authenticity.
In conclusion, I must mention three slyptic representa-
tions of Leeuwenhoek. The first is the profile portrait on
the silver medal awarded to him in 1716 by the University
of Louvain (see p. 80). This has already been depicted by
van Loon and Haaxman. The medal is now in the Gemeente-
museum at Delft; and as it was struck during his lifetime, its
fA ee
1 Tt was exhibited at the Leeuwenhoek Celebration in 1875, and was
described by Harting (1876, p. 120). I think the picture was very probably
intended as a title-page for the projected edition of L.’s letters (following
No. 146 and preceding the Send-brieven) which was never published in
Dutch or Latin.—According to de Lint (1931) the original is now in the
collection of Dr J. van der Hoeven at Eefde [near Zutphen]. It is
reproduced in Opusc. Select. Neerland., Vol. IX, Pl. III (1931).
2 Given in full on p. 299 supra.
“ce
356 LEEUWENHOEK AND HIS “LITTLE ANIMALS”
maker may well have had Leeuwenhoek himself as a model.
The portrait is therefore worth consideration. The second
carved likeness is the white marble medallion on his tomb (see
p. 100, and Plate XV). This was made after his death, and
was probably modelled on the silver medal. It has less interest,
therefore, as a portrait. The third representation is that on
the “ Leeuwenhoek Medal,” awarded every ten years by the
Royal Academy of Sciences of Amsterdam to persons who have
distinguished themselves as microbiologists.' This medal is of
gold, valued at f.300 (about £25), and has been described and
figured by Harting (1876). The portrait which it bears is,
however, a modern fake; and its historico-iconographical
value is consequently mil.
(vii) LEEUWENHOEK’S “FIRST 27 UNPUBLISHED
LETTERS ”
As Leeuwenhoek’s own collective editions of his works—
both Dutch and Latin—begin with a letter called “No. 28”,
dated 25 April 1679, it has generally been assumed that all his
earlier letters (No. 1—No..27) have been lost. But this is not
so: most of them have been preserved among the Royal
Society MSS., and many have been printed in English or Latin
(generally abbreviated) in the early volumes of the Philosophical
T'ransactions.
I have discussed these letters in some detail in an article
about to appear in Opuscula Selecta Neerlandicorum, Vol. IX,
so I need not repeat what I have there said.” But as my
numeration differs entirely from that of Vandevelde—who
previously attempted to arrange and number them without
consulting the original manuscripts—and as I have made
frequent references to these letters in the foregoing pages, I
give here a tabular synopsis for the reader’s convenience and
culdance.
1 The first award was made to C. G. Ehrenberg in 1875. The later
recipients have been Ferdinand Cohn (1885), Louis Pasteur (1895),
M. W. Beijerinck (1905), David Bruce (1915), and F. d’Herelle (1925).
2 Since these lines were written, the article has appeared in print: see
Dobell (1931).
TABULAR SYNOPSIS
357
LEEUWENHOEK’S “FIRST 27 LETTERS”
Letter
Addressed to Date Roy. Soc. MS. Published in Phil. Trans.
H. Oldenburg ? [No MS.] | Vol. VIII, No. 94, pp. 6037-6038.
[Transmitted 1673. [Extracts, in English. ]
by de Graaf | Vol. VIII, No. 97, pp. 6116-6118.
28 Apr. 1673] 1673. (Figures, with description in
English. ]
H. Oldenburg | 15 Aug. 1673 | L.1. 1 | Vol. IX, No. 102, pp. 21-23 and
23-25 [in 2 parts]. 1674. [Extracts,
in English.]
H. Oldenburg! 7 Apr. 1674 | L.1. 2 | Vol. IX, No. 102, pp. 23-25. 1674.
[Combined with part of Letter 2,
| Extracts only, in English. ]
H. Oldenburg | 16 Apr. 1674 | L.1. 83 | Unpublished
Lys Ee Sa ee eee Lia Ala Pa Ne
H. Oldenburg | 1 June 1674 | L.l. 4 | Vol. IX, No. 106, pp. 121-128. 1674.
[Part only—in English. ]
H. Oldenburg | 6 July 1674| L.1. 5 | Vol. IX, No. 106, pp. 128-131. 4674.
| [Extracts only—in English. ]}
H. Oldenburg | 7 Sept.1674 | L.l. 7 Vol. IX, No. 108, pp. 178-182 [mis-
printed 821]. 1674. [Incomplete
English translation. ]
H. Oldenburg | 7 Sept.1674 | L.1l. 6 Unpublished
H. Oldenburg | 19 Oct. 1674 | L.1. 8 | Unpublished
H. Oldenburg | 4 Dec. 1674 L.1. 9 | Vol. X, No. 117, pp. 378-380. 1675.
[Extracts in English. ]
H. Oldenburg | 22 Jan. 1675 | L.1. 10 | Unpublished
H. Oldenburg | 11 Feb. 1675 | L.1. 11 | Unpublished
H. Oldenburg | 26 Mar. 1675 | L.1. 13 Unpublished
H. Oldenburg | 14 Aug. 1675 | L.l. 15 Vol. X, No. 117, pp. 380-385. 1675.
(Extracts, in English.]
H. Oldenburg ; 20 Dec. 1675 | L.1. 16 Unpublished
H. Oldenburg | 22 Jan. 1676 | L1. 16a | Unpublished
H. Oldenburg | 22 Feb. 1676 | L.1. 17 Unpublished
H. Oldenburg | 21 Apr. 1676} L.1. 18 Vol. XI, No. 127, pp. 653-656. 1676.
[Incomplete English translation,
with notes (by Nehemiah Grew).]
H. Oldenburg | 29 May 1676} L.1. 20 Unpublished
R. Boyle 28 July 1676 |[ With Unpublished
Boyle MSS.]
H, Oldenburg | 9 Oct. 1676 | L.1. 22 Vol. XII, No. 133, pp. 821-831. 1677.
[Incomplete English translation. }
358
LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
SYNOPSIS OF LEEUWENHOEK’S “ FIRST 27 LETTERS ’’—continued
Letter
No.
21
21a
24
25
26
27
Addressed to
H. Oldenburg
Viscount
Brouncker
Viscount
Brouncker
R. Hooke
N. Grew
N. Grew
N. Grew
N. Grew
H. Oldenburg
H. Oldenburg
H. Oldenburg
Date
30 Oct.
23 Mar.
14 May
5 Oct.
16 Oct.
.. Nov.
14 Jan.
18 Mar.
31 May
27 Sept.
21 Feb.
1676
1677
1677
1677
1677
1677
1678
1678
1678
1678
1679
Roy. Soc. MS.
L.1. 24
L.1. 25
ly 2
ed; 29
L.1. 32
[No MS.]
L.1. 33
Lil. 34
L.1. 36
Ll. 88
[No MS.]
Published in Phil. Trans.
Unpublished
Vol. XII, No. 134, pp. 844-846. 1677.
{Incomplete English translation. ]
Vol. XII, No. 136, pp. 899-905. 1677.
[English translation. A full Latin
translation of this letter was pub-
lished later in Derham’s Philos.
Ezpts. & Obss. of R. Hooke (1726),
pp. 65-74. ]
(Not in Phil. Trans. English ex-
tracts published in R. Hooke’s Lect.
& Collect, (1678), Part II, Letter 1,
pp. 81-83: reprinted in his Lect.
Cutlervanae (1679).]
Unpublished
Vol. XII, No. 142, pp. 1040-1043.
1679. [Full letter, in Latin. ]
[Not in Phil. Trans. English ex-
tracts published in Hooke’s Lect. €
Collect. (1678), Part II, Letter 2,
pp. 84-89: reprinted in his Lect.
Cutlervanae (1679). ]
Vol. XII, No. 142, p. 1044. 1679.
(Abstract, in Latin. }
Vol. XII, No. 140, pp. 1002-1005.
1678. [Two extracts, in English.]
Vol. XII, No. 142, p. 1045. 1679.
[Latin summary of another part of
letter. ]
Unpublished
Unpublished [This letter is men-
tioned by L. in his letters dated
13 June 1679 (No. 28a, unpublished),
13 Oct. 1679 (No. 280, unpublished),
and 25 Apr. 1679 (No. 28— published
in Dutch and Latin printed works).
It was apparently lost in trans-
mission. ]
Addendum.—All the Letters marked ‘‘ Unpublished” in the foregoing
list have now (with the exception of the last, which still remains lost) been
printed in full in Vol. IX of Opuscula Selecta Neerlandicorwm, Amsterdam,
This volume has appeared too late for its contents to be considered
in the present work.
1931.
LEEUWENHOEK’S SEALS 359
In addition to the information given in this table, I must
note the following points:
(1) Leeuwenhoek sent a complete copy of his Letter 4
(1 June 1674, to Oldenburg) to Const. Huygens, and the MS.
is preserved at Leyden. ‘This copy has recently been printed
by Vandevelde and van Seters (1925).
(2) Letter 19 (23 March 1677) and Letter 21 (5 Oct. 1677)
are quoted extensively by Leeuwenhoek himself, in his own
language, in his Letter 96 (9 Nov. 1695, to the Elector Palatine)
printed in the Dutch works—with Latin versions, of course,
in the corresponding Latin editions.
(3) Letter 22 (Nov. 1677) is quoted, almost entire, in its
original Dutch, by Leeuwenhoek in his Letter 113 (17 Dec.
1698, to Harmen van Zoelen—published in the collective
editions) : and a complete English translation of it (made but
not published by myself) has now appeared in the recent
work of Cole (1930).
(4) Finally, I must note that the printed Catalogue of the
Royal Society MSS., compiled many years ago by the youthful
Halliwell-Phillipps (1840), is not free from errors; and
accordingly its entries relating to the Leeuwenhoek MSS. are
not to be accepted as invariably accurate.
(viii) LEEKUWENHOEK’S SHALS
Seals on old manuscripts are often important for purposes
of identification: how important they may sometimes be, I
know from the following incident. Recently, Carbone (1930)
believed that he had discovered a new Leeuwenhoek letter
among the Magliabecht MSS. in the National Library at
Florence. This document was among the genuine letters of
Leeuwenhoek addressed to the Florentine scholar, but was
unsigned. Carbone reproduced it in facsimile—including the
seal (enlarged). From its contents it was at once evident
to me that this letter (written in Latin, and dated 2 May 1692
from Hanover) could not possibly have been written by
Leeuwenhoek. I guessed immediately, however, that it was
written by Leibniz: and on comparing it with Leibniz’s
extant letters to the Royal Society, I found that the cor-
rections throughout were apparently made in his handwriting,
and that the seal was one which he used. A seal is often
as good as a signature (for no man lent his seal-ring to
360 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS”
others), and I therefore felt satisfied that the letter was written
by Leibniz and not by Leeuwenhoek. This I was soon able to
confirm by discovering that the manuscript in question had
actually been published previously as a genuine Leibniz letter
by Targioni-Tozzetti (1746, pp. 119-122).
Leeuwenhoek’s own seals have never yet been described.
At various periods of his life he sealed his letters with at least
three different ones—usually of red wax, but occasionally of
black. Most of the extant impressions are imperfect—the
seals having generally been broken, of course, in opening the
letters. The following notes are put together from the avail-
able fragments. They may assist future students in identifying
his writings, but are as incomplete and imperfect as their
originals. :
(1) Most of the early epistles are sealed with the monogram
shown in Plate XXXII (upper figure). This is taken from an
almost perfect impression on Letter 3a (16 April 1674)—
stamped from an oval die measuring approximately 16 mm. by
14mm. The letters APL presumably stand for A[ntony]
P[hilipszoon| L[eeuwenhoek] ; the rest of the device I cannot
interpret with any confidence. Above, there appears to be an
arabic numeral 4: below, connected by a vertical line, the
roman figure xx or (more probably) xxv can be read.
(2) Another early seal—which I am unable to reproduce—
was a heraldic device, all extant impressions of which are
more or less fractured or indistinct. The die was apparently
oval, about 17 mm. by 16 mm., with a slightly beaded border.
The available examples show a small shield, bearing four
raised vertical lines, surmounted by a helmet. On the field
behind are various irregularly distributed plumules (?), but no
lettering or other recognizable figures. This seal is affixed to
several early signed and authentic letters to the Royal Society
(including No. 13, 20 December 1675, from which an extract
is here translated). The armorial bearings I have been unable
to identify. I can only add that an identical scutcheon with
four vertical lines is several times figured by Boitet (1729) as
the coat-of-arms of the Uttenbroek family—a family with
which Leeuwenhoek is not known to have been connected.
(3) Nearly all the later letters, when sealed, bear a portrait
of Leeuwenhoek himself. The die used for this seal (see
Plate XXXII, lower figure) was evidently cut with very great
care and precision, and the various impressions—in red (rarely
facing p.
360
TWO OF LEEUWENHOEK’S SEALS
Enlarged.
For description see the text.
PLATE
a7
a 2
r us eur ge hr aa yr
re eh » a ako oat 0 ee
'”
LEEUWENHOEK’S SEALS 361
in black) wax—show an astonishing amount of detail when
closely studied. The seal was obviously copied from Verkolje’s
mezzotint portrait of Leeuwenhoek (1686): it shows his
bewigged head, as there depicted, with a curtain behind, and
even reproduces such minutiae as his little moustache. Most
impressions, however, are faulty or badly fractured. The best
(from which my figure here is reproduced) is on Maria’s letter
to the Royal Society." I judge the original die to have
measured—outside its beaded border—approximately 21 mm.
by 18mm. But I cannot be sure, as most impressions are so
imperfect. (The specimen figured by Carbone (1930) is
extremely poor.)
This seal cannot have been used by Leeuwenhoek before
1686, when Verkolje made his mezzotint. It may therefore
possibly help to date some of his undated letters in future.
The artist who cut the die is not known; but he must have
been extremely skilful, for his work reveals—on careful study
of good impressions—a degree of accuracy in reproducing
minute detail which is really remarkable. Unfortunately, the
dies of all the seals are now lost.
SIMPLEX SIGILLUM VERI
1 See p. 98 supra. There are two seals on this letter, but only one is
perfect. The other is distorted by a slip in impressing the wax.
362
ENVOY: LEEUWENHOEK’S PLACE
IN PROTOZOOLOGY AND BACTERIOLOGY
Protozoology and Bacteriology ”’, and I now repeat this
title—which has since been adopted by others—on the
title-page of the present work. I do this designedly, because
in my opinion he alone deserves this designation. In my
opinion (which has not been formed too hastily) he was the
first man who ever saw living protozoa and bacteria under
a lens, and by correctly interpreting and describing his obser-
vations he created the modern disciplines of Protozoology and
Bacteriology. Consequently, his relation to these sciences is
that of “father” or “only begetter’”’.
Nevertheless, there are still some people who dispute
Leeuwenhoek’s claim to the discovery of the Protozoa and the ~
Bacteria, while there are others who bestow upon him titles
which he does not deserve—as he himself would freely have
confessed. He has already been styled “Father” and
‘Founder ’”’ of Micrography by Blanchard (1868) and Vande-
velde (1922)—to mention no other authors: though it is
obvious that Pierre Borel and Henry Power and Robert Hooke
and Marcello Malpighi have all at least as good a right to the
title. Launois (1904) obviously goes rather too far when he
calls Leeuwenhoek one of the “ Fathers of Biology’’: there is
more evident justification for those who regard him as the
“Father ” of Histology or Cytology or Haematology ‘"—or even
as just the First Milk-Analyst.” Almost every writer who
discusses Leeuwenhoek’s work regards him, apparently, as
“father” of his own speciality—some strangely misinformed
but enthusiastic authors even hailing him as “the Inventor
A FEW years ago I called Leeuwenhoek “Father of
1 Sabrazés (1926).
2 Wynter Blyth (1903).
THE ENVOY 363
of the Microscope”.’ Many such claims are manifestly
absurd; yet his own right to be regarded as the Father of
Protozoology and Bacteriology is, I believe, real and
indisputable.
The discovery of the microscope is still in dispute, but I
need not discuss the subject here. Its invention is intimately
bound up with that of the telescope, and the rival claims of
Italy and Holland in this connexion have been ably defended
in recent times by Govi (1888), and Harting (1850) and de
Waard (1906) respectively. The question has also been
critically considered lately by Singer (1921) and Disney (1928).
For present purposes it will suffice to note that one form of
the microscope (¢.e., the compound microscope, to which the
name is properly applied) was probably devised in Holland in
the first decade of the XVII Century (not earlier), while
immediately afterwards another form was independently
discovered in Italy. But Leeuwenhoek probably knew nothing
of all this, and it is unnecessary to argue here about the
priority of Zacharias Janssen, Lipperhey, Drebbel, Galileo, or
any other possible “inventor of the microscope”. Leeuwen-
hoek did not use a microscope, but only a simple lens; so
that the invention of the compound instrument (which
occurred before he was born) has no bearing whatsoever upon
his own work or discoveries.
The discovery of simple lenses is, however, also a subject
of dispute. It is now known, from the profound researches of
the French scholar Martin (1871), that the ancients knew
nothing about magnifying-glasses—notwithstanding the con-
fident assertions of Dutens and many another more recent
writer. Our Roger Bacon® (circa 1214-1294) had at least a
glimmering of the properties and possibilities of lenses, but
the first were probably made, and used as spectacles, about
1 Byen since these lines were written I have read a paper (Chapman,
1931) in which it is said that L.’s observations “ have earned for him the
title of ‘The Father of Microscopy ’.”
2 This excellent and fully documented work appears to have been over-
looked by all recent writers on the history of the microscope—including
Singer and Disney.
3 Of. Bridges (1914). In this connexion the reader may also consult
with profit the recent historical analyses by Singer (1921) and Disney e¢ al.
(1928). The literature dealing with Bacon is too vast to cite here.
364 LEEUWENHOEK AND HIS “LITTLE ANIMALS”’
the year 1300 in Italy—their popularization “for the help of
poor blind old men” being chiefly due to the pious and
private labours of the monk Alessandro de Spina of Pisa.
The actual inventor of spectacles, however, is said to be a
Florentine—Salvino d’Armato degl’Armati.’ Friar Bacon
and his brethren in Italy were probably the originators of
simple lenses; and the unknown people who first wore
spectacles and used ordinary magnifying-glasses—for assis-
tance in reading or for personal amusement—are the real
“precursors ” of Leeuwenhoek as a “ microscopist ”’.”
According to Govi (1888), the word “ microscope”
(microscopio) was invented by Giovanni Fabri*—one of the
earliest members of the Accademia dei Lincei—who first used
it in a letter to Federigo Cesi dated 13 April 1625. The first
pictures made with the aid of this instrument are usually
supposed to be those of the bee and weevil interpolated by
Francesco Stelluti (1630) in his Italian translation of the
poems of Persius. The first “micrography ” is the Century
of Microscopic Observations by Pierre Borel,* published in
Latin at The Hague in 1656: but it was soon followed by the
similar work of Henry Power’ (1663-4) and the more
celebrated Micrographia of Robert Hooke (1665)—both
written in English and printed in London.
The writings of Stelluti and Borel and Power and Hooke
all antedate anything that Leeuwenhoek ever published.
But when he wrote his first letters he had probably never
heard of any of these authors: and as he could read neither
English nor Latin nor Italian, they could have afforded him
1 Cf. Redi (1678), Mensert (1831), Harting (1850), Pansier (1901), etc.
2 I cannot refrain from mentioning here a remarkable fantasy recently
published by our greatest living English poet and novelist—an unhistorical
story revealing more than superficial historical knowledge. I refer to
Rudyard Kipling’s “The Eye of Allah”, printed in his volume entitled
Debits and Credits (8° London, 1926).
3 Fabri or Fabro, in Italian. His real patronymic was Faber, and he
was descended from a family of this name who came from Bamberg in
Bavaria. Cf. Carutti (1883, pp. 25, 39), ete.
4 Pierre Borel, alias Petrus Borellus (1620-1689), a French physician,
antiquary, and philologist. Cf. Nowv. Biogr. Gén., VI, 697.
* Henry Power (1623-1668), M.D. Educated at Christ’s College,
Cambridge, and practised as a doctor at Halifax. He was one of the first
Fellows of the Royal Society—having been elected in 1663.
THEE ENVOY 365
little help—even had he seen their works. Moreover, there
are no descriptions of protozoa or bacteria in any of these
publications—so far as I have been able to ascertain. I have
studied them all with care, but have sought information on
such organisms in them in vain. I believe they contain none,
and nobody (to my knowledge) has yet proved that they do.
Nobody now claims that Fabri or Stelluti or Power or Hooke
discovered the Protozoa or the Bacteria: but a half-hearted
claim has recently been made for Borel by Singer (1915), so
I cannot altogether ignore it here.
Borel (1656) tells us that “worms” are said to be found in
the blood of people suffering from “ fever”’,' though he makes no
claim to have seen such things himself. Yet Singer says” that
to him “It seems . . . highly probable that he caught a
glimpse of infusoria and possibly bacteria, for he assures us that
all decomposing material swarms with similar worms.” Singer
gives no exact reference to the passage on which he relies, but
apparently alludes to Borel’s Observatio de Sanguine ; in which
he does not give any such assurance, but merely says it zs
probable that worms would be found in every decomposing
material if attention were paid to it.’ The whole passage is
clearly hypothetical. As a prophecy it may have some interest
for helminthologists: for the protozoologist or bacteriologist it
is obviously without significance. Something more than a
misreading or mistranslation of Borel’s words is surely needed
to prove that he forestalled Leeuwenhoek.
Another claim to priority in the discovery of the Bacteria
has been put forward for the German Jesuit priest Athanasius
Kircher (1602-1680)—well known as a voluminous and reckless
writer on all manner of subjects.* I do not pretend to have
1 Certo etiam refertur, in sanguine febricitantium vermes reperiri.
2 Singer (1915), p. 338. Singer’s references to Borel are not always
easy to follow. In two places, indeed, he appears to confuse Borel’s work
of 1656 with his earlier publication of 1653. But this—so far as I can
discover—contains only one trivial reference to the use of the “ engyscope”’
[= microscope], having no bearing on the present subject. Borel’s later
observation (1656a, p. 198) on “ whale-like insects in human blood ’’—to
which Singer also alludes—cannot conceivably refer to either protozoa or
bacteria.
3 quare verisimile est idem in omni re, dum putrefit, contingere, si animad-
vertatur (Borel, 1656; Obs. III, p. 8).
4 Cf. Nouv. Biogr. Gén., XXVII, 769, and Allg. Dtsch. Biogr., XVI, 1.
366 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS”’
read all his works (which is probably impossible and would
certainly be unprofitable), but only some parts of those which
deal with biological topics. In none of them can I find any
evidence whatsoever to indicate that he ever saw or described
either a protozoon or a bacterium. But others believe that
they have been more fortunate, so I must briefly consider their
findings.
The first person to credit Kircher with the discovery of
the Bacteria was, I believe, Friedrich Léffler (1887), who
opens his work on the history of bacteriology with a quotation
from the Scrutinium Pestis (1658)* wherein Kircher says:
“That air, water, and earth are swarming with countless
insects, is so certain that it can even be proved by ocular
demonstration. It has hitherto also been known to everybody
that worms swarm out of rotting bodies: but only after the
wondrous invention of the Microscope did it become known
that all decomposing things swarm with an innumerable
brood of worms invisible to the naked eye: which even I
myself would never have believed, had I not proved it by
repeated experiment over many years.” *
Now this passage contains no obvious reference to any
organisms other than worms or insects—well known to
everybody at the time when Kircher wrote: yet for reasons
unexplained Léffler alleges that it “announces . . . the
discovery of a new world of living creatures” —by which he
means, presumably, the Bacteria. But does it? Surely not.
The assumption is so far-fetched, indeed, that Léffler felt
constrained to add that ‘“ Kircher was unable to give any
more accurate data regarding these worms;” and he then
made an irrelevant reference to the Ars Magna Lucis et
Umbrae (1646). Any ordinary person would conclude that
Kircher never described bacteria for the simple reason that
he never saw them—and because Leeuwenhoek had not then
1 Léffler actually quotes (in German translation) from an edition of
1671, but gives no exact reference to the passage. I have not seen this
edition, but it appears to be a reprint of the first Leipzig edition (1659),
which I possess. In this the passage quoted (from Cap. VII, § II) is on
p. 69. I have to thank Dr Singer for kindly lending me his own copy of
the original edition of 1658.
2 T translate from the original dog-latin of Kircher (1658)—not from
Loffler.
THE ENVOY 367
published his discoveries. The organisms which Leeuwenhoek
discovered were, for those times, of a ‘“Stupendious
Smalness’’;* and there is good reason to believe that Kircher
possessed no instruments capable of showing any objects of
the order of magnitude of common bacteria.
Singer (1914), however, has recently reasserted Léffler’s
claims, and has attempted to support them with translated
quotations from Kircher’s “ Experiments” with rotting flesh,
leaves, and wood. ‘These are really too ridiculous to quote.”
It is obvious—from Kircher’s own words—that he saw nothing
but maggots, mites, and nematodes, such as anybody possessed
of asimple low-power magnifying-glass can nowadays perceive.
I have consulted all the passages on which Léoffler and Singer
rely, and have repeated some of Kircher’s so-called experiments:
and I have even read a considerable part of the Scrutiniwm
Pestis and of the Ars Magna, and have made long search in
Buonanni’s Micrographia Curiosa (1691) and Musaeum
Kircherianum (1709). But the results have been incommen-
surate with my labours. T'o me the Scrutiniwm Pestis appears
as a farrago of nonsensical speculation by a man possessed of
neither scientific acumen nor medical instinct.’ Kircher
obviously had no conception of a real experiment—in the
Baconian and modern sense. It is easy enough, of course, to
tear a line here and there from his voluble writings, and to
use it as evidence on his behalf: but if such lines be considered
in their context they have a very different complexion. For
instance, some recent authors have inferred that Kircher’s
remarks about rats dying and decomposing at atime of plague
show that he realized the relation of these rodents to plague-
1 Grew (1701), p. 12.
2 About ten years ago I had some correspondence with Dr Singer on
this matter, and I then attempted to convince him of the error of his views.
From his last letter to me on the subject I gather that he is no longer
prepared to defend Kircher’s claim to the discovery of either the Bacteria or
the Protozoa, and that he now accepts my interpretations.
8 Kircher—who was a priest with no biological or medical training—
had obviously derived most of his “ knowledge” from wide reading, and it
seems to me not unlikely that in his vague references to ‘ worms”’ occurring
in the blood of sick people he was merely harking back to the speculations
of antiquity: for example, to the well-known passage where Pliny says
“nascunturque in sanguine ipso hominis animalia exesura corpus ”’
(Hist. Nat., lib. XX VI, cap. xiii; ed. Genevae 1582, p. 488).
368 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS ”’
epidemics. Iwish such authors would also explain, in modern
terms, what Kircher meant when he recorded further how
plague could arise likewise from a rotting mermaid.
For my part, I cannot regard Kircher as anything more
than the veriest dabbler in Science. His own writings
appear to me unscientific in the highest degree, and I can find
no evidence that he ever saw—even by chance—a protozoon
or a bacterium through his “smicroscope.” His writings
appear, consequently, to furnish no evidence whatsoever to
prove that he forestalled Leeuwenhoek. But asI have already
said, I have not read all his works. I can therefore only beg
his supporters (if any there still be) to adduce some solid
passage—which I have hitherto been unable to discover in his
vast publications—to prove that he ever saw a protozoon.
(Discussion of his “ discovery’ of the Bacteria may well be
postponed until it has been demonstrated that he observed
these larger organisms.) I am aware, of course, that Garrison *
calls Kircher “the earliest of the microscopists”’ and says
that he was “ undoubtedly the first to state in explicit terms
the doctrine of a ‘contagium animatum’ as the cause of
infectious diseases”’: but I submit that these statements also
have not yet been substantiated, and I cannot conceive that
they ever will be. Microscopists and contagiwm animatum
both existed before Kircher began to write.
This brings us to another line of argument against
Leeuwenhoek’s originality—the argument from the doctrine of
contagium vivum. It is as certain as anything historic ever
can be that Kircher was not the first exponent of this idea:
and there can be no doubt that the part played by “ animal-
cules” in the causation of diseases was foreshadowed long
before either Kircher or Leeuwenhoek was born.’ Some of the
oldest known authors appear to have been familiar with the
1 Garrison (1921), p. 250.
2 In this connexion the paper by Singer (1913) should be mentioned,
though I must confess that I have been unable to verify many of his
statements and references.
3 IT do not deny, of course, that Kircher formulated a “ doctrine of
contagium animatum’’—and possibly more explicitly than his predecessors :
but I do deny that it had any more objective basis than similar earlier
guesses. The doctrine had no concrete foundation before L.’s discovery of
real “ animalcules.’’
THE ENVOY 369
concept of a living “ contagion ” or infective agent—invisibly
floating in the air at the time of epidemic pestilences, and com-
parable with some kind of “insect”. Malaria, for example,
was all too well known in classical times, and even rustic writers
such as Varro‘ (116-27 B.c.) and Columella (florwit ca. A.D. 50)
cuessed that the “insects” abounding in marshes have some
causal connexion with “fever’’.* (The ancients even used
mosquito-nets as a prophylactic.) At a much later date
Lancisi (1718) developed a more coherent and modern theory
of malarial infection: yet even in his hands it remained nothing
but an ingenious speculation.’ The true aetiology of malaria
has become known only in the last fifty years. In Leeuwen-
hoek’s day both the malarial parasite and its mode of
transmission by the mosquito were still wholly unknown to
mankind, and the guesses of his predecessors and contem-
poraries have really no bearing upon his own discoveries.
Nobody before Leeuwenhoek ever saw a living protozoon, and
1 Marcus Terentius Varro (who was no mere husbandman) is particularly
noticeable because of his antiquity. He is frequently cited, but seldom
correctly. In all his extant works there appears to be but one passage
bearing on the aetiology of malaria: and as most editions of his writings
are rare, and as the passage in question is very short, I may quote it here.
Discussing sites appropriate for a country house, Varro notes certain places
to be avoided (such as the banks of a river—apt to be too cold in winter
and unhealthy in summer) and then adds: ‘‘ Attention should also be paid
to any marshy places thereabouts ; both for the same reasons, and because
[they dry up,] certain minute animals grow there, which cannot be detected
by the eye, and which get inside the body from the air, through the mouth
and nostrils, and give rise to stubborn distempers.” (Advertendum etiam
siqua erunt loca palustria, et propter easdem causas, et quod [arescunt,]
crescunt animalia quaedam minuta, quae non possunt ocult consequi, et per
aera intus in corpus per os, ac nares perveniunt, atque efficiunt difficilis
morbos.) Of. Varro, lib. I, cap. XII (Script. Rez Rust., ed. 1543, p. 54 recto).
The words in square brackets should probably be omitted—arescunt being a
MS. misreading or dittography of the word following.—Since writing the
foregoing note I find there is now an excellent English edition of Varro by
Storr-Best (1912): nevertheless, I let my own translation of the passage
stand.
2 The references to malaria in the Latin classics are mostly collected in
the recent posthumous work of Celli (1925), while the Greek literature has
been ably reviewed by Jones (1909).
3 Lancisi actually refers to L.’s discoveries in order to prove the existence
of such extremely minute animalcules as he himself postulated. Cf. op. cvt.
p. 46.
24
ce
370 LEEUWENHOEK AND HIS “LITTLE ANIMALS ”’
all early speculations about the relation of “insects” to
malaria belong properly to the -prehistory of entomology—not
to that of protozoology.
The whole history of bacteriology has recently been so
admirably written by Bulloch (1930) that I can add nothing to
his account of its origins.” He has shown quite clearly that
real bacteriology (like real protozoology) began with Leeuwen-
hoek’s discoveries, though it was preceded by a long period of
speculation on the causes of contagious diseases. Some early
writers, it is true, made astonishing guesses at the existence of
bacteria—particularly Fracastoro (1478 or 1483—1553), whose
hypothetic “ seminaria”’ bear a remarkable resemblance to
modern ‘germs’ or “microbes”.? But nobody before
Leeuwenhoek ever saw a bacterium with his own eyes.
Nebulous though ingenious notions about invisible living
organisms floated in the air for some thousands of years : but
it required the untutored genius of a Leeuwenhoek to condense
them—single-handed and with only his own little home-made
‘““microscopes”’—into the concrete realities of present-day
laboratories and text-books of bacteriology.
Another point should not be overlooked in this connexion.
When Leeuwenhoek announced his discovery of the
“animalcules”” in various waters and infusions, it was
universally regarded as something entirely new. Yet the
earlier writings of Kircher and others had already been public
property for some years. Why, then, were contemporary
‘“ philosophers ’”’ astounded at Leeuwenhoek’s “ discoveries ”»—
if they were not real discoveries? And why did some
contemporary and later critics dispute his observations ?
Why did no author of his time—including Kircher, who was
still alive and busy writing—claim priority? It is surely
strange, to say the least, that nobody before Loffler in 1887
ever connected Leeuwenhoek’s concrete discoveries of 1676
with Kircher’s random speculations and “experiments” of 1658.
1 T may note, however, that I have studied most of the early writings
mentioned in this fine and accurate work: but as I agree entirely with its
conclusions, and as it has an authority far beyond anything to which I can
pretend, I shall here dispense with all other references to the subject.
2 I cite the work of Fracastoro because I have devoted particular atten-
tion to his writings, owing to their great historic interest. On Fracastoro
see also C. and D. Singer (1917).
THE ENVOY 371
All Leeuwenhoek’s contemporaries regarded him as
unquestionably the discoverer of his “little animals”. But
his discoveries were soon confirmed by Hooke—as we have
already seen—and by several other “philosophers”. In the
last decade of the XVII Century the work of Buonanni' (1691)
appeared, containing the first pictures of free-living ciliates,
but reaffirming the doctrine of spontaneous generation—a
small advance and a big step backwards at the same time.
Of much greater importance were the papers by King’ (1698)
and Harris * (1696), who both saw and described a variety of
free-living protozoa and bacteria—tfrankly in imitation of
Leeuwenhoek, but adding new facts and some original
speculations. Of far less value, protozoologically, were the
notes by Gray * (1696, 1697), who observed protozoa with his
ingenious “ water-microscope” but gave only a slight account
of what he saw. These five men—Hooke, Buonanni, King,
Harris, and Gray—must all be regarded as belonging to the
first generation of protozoologists.
But by far the greatest scion of this generation still
remains unknown to us by name. In two anonymous
English publications’ which appeared in the Phil. Trans. in
1703 are to be found some amazingly good figures of free-
1 Filippo Buonanni, alias Philippus Bonannus (1638-1725), an Italian
Jesuit priest.
2 Sir Edmund King (1629-1709), M.D.; physician to Charles II, whom
he attended during his last illness. He was elected F.R.S. in 1666.
* The Rey. John Harris (1667 ?-1719), D.D., rector of Winchelsea in
Sussex, F.R.S. (1696). Author of Lexicon Technicum (1704).
* Stephen Gray (?-1736) was a physicist, who published a number of
papers in the Phil. Trans. He was not made a Fellow of the Society
until 1732.
> See Anonymus (1703,1703a). The first paper consists of extracts from
several letters written in 1702 and “communicated by Sir C. H.” [= Sir
Charles Holt, not a Fellow] : the second comprises two other letters (1703)
from “a Gentleman in the Country ”, communicated by “ Mr. C.” [probably
John Chamberlayne]. All these letters were really written by the same
person, whose identity I have vainly endeavoured to discover. The letters
themselves are not in the Society’s archives or the British Museum (so far
as I have been able to ascertain), and all the documents relating to them
appear to have been destroyed. In view of their great interest, I have made
repeated attempts to discover their authorship; but every clue has proved
unavailing, and I fear that “The Gentleman in the Country” covered up
his tracks on purpose—in order to remain anonymous for ever.
372 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
living protozoa and bacteria, and diatoms '—confirming and
amplifying many of Leeuwenhoek’s findings and accompanied
by a commentary, light-hearted and conversational, which
shows nevertheless remarkable insight and ability. The
pictures were far ahead of anything previously published, and
are sufficient alone to establish their draughtsman as Hldest
Son of the Father of Protozoology.
Only one other protozoologist of Leeuwenhoek’s period
deserves notice here—Louis Joblot (1645-1723), a French-
man. His observations were first published in 1718,’ and
attracted little notice at the time: but his book is, in fact,
the first special treatise on the Protozoa, and it contains
descriptions and figures of many forms not previously
described. A recent writer* has tried to show that Joblot
was not merely a follower of Leeuwenhoek, but actually his
equal—an independent co-discoverer of the Protozoa. But
such a suggestion is manifestly groundless. There is no
evidence that Joblot studied the Protozoa as early as the
time when their discovery was announced by Leeuwenhoek ;
and the appearance of his book in the next century—only five
years before they both died—definitively assigns his publication
to a later generation. In Joblot’s writings there is no direct
reference to Leeuwenhoek’s discoveries, but much internal
evidence of imitation.’
I have already had occasion to note’ that Leeuwenhoek
himself made no application of his discovery of “‘ microbes’”’
to medical doctrines of contagion. He discovered protozoa
and bacteria not only in waters and infusions but also in the
1 Tabellaria—the first account and figures of this organism. Most of
the other figures are equally easily recognizable.
2 On Joblot see especially Fleck (1876), Cazeneuve (1893), Boyer (1894),
Konarski (1895), Brocard (1905), and Dobell (1923). I may note here that
the work of Sturm (1676), cited by Ehrenberg and others as containing
contemporary observations on “‘infusoria’’, really deals only with insects
and nematodes—not with protozoa. It should not be quoted in this
connexion.
3 This work is now very rare, and is better known from the much later
and comparatively common edition of 1754.
4 Konarski (1895).
° Cf. Dobell (1923).
* See p. 230 supra.
THE ENVOY Sle
bodies of living animals—including man: but he never in his
writings suggested, so far as I am aware, that his discovery of
such “animalcules” threw any light upon the aetiology of
morbid infections or furnished, for the first time, an objective
basis for the old speculations regarding the existence of
“living germs” of diseases—seminaria morborum, contagium
vivum, contagium animatum, and the like. Yet this applica-
tion of his findings was immediately made by others. Within
a few months of the appearance of his Letter 18, announcing
the discovery of the “little animals” in all manner of liquids,
we find “an observing person in the country” writing to the
editor of the Philosophical Transactions as follows': ‘‘ Mr.
Leewenhoecks Microscopical Discoveries are exceeding curious,
and may prompt us to suspect, that our Air is also vermicu-
lated, and perhaps most of all in long Calms, long-lasting
Eastern Winds, or much moisture in Spring-time, and in
seasons of general Infections of Men or Animals.”
As soon as this possible connexion between demonstrable
“animalcules” and hypothetic infectious “germs” was
suggested, it became almost commonplace : its theoretical im-
plications and its obvious practical applications were henceforth
recognized. Yet nobody made any real use of them during
the next century anda half. Mankind possessed the necessary
data, and was inspired—as usual—by the appropriate ideas :
but the course of history has shown that both knowledge
and notions arrived prematurely. We should not blame
Leeuwenhoek, therefore, for making discoveries before they
could be appreciated properly either by himself or by the world
at large. Rather should we censure, I think, those modern
writers who do not take his work into consideration when
discussing present-day problems. ‘To me it is incomprehensible
how one author in my lifetime could have defended a thesis on
Parasitology in the XVI and XVII Centuries,’ and another
could have written a book on The Discovery of the Microbic
1 See Anonymus (1677). Cf. also the words of Slare (1683), quoted
already on p. 230.
2 Rémignard (1902). This dissertation—approved by the great Raphael
Blanchard—contains only two ridiculous references to L. The first (p. 55)
merely alludes to the fact that he did not discover Demodex, while the
second (p. 63) informs us that he believed in the spontaneous generation
of frogs.
374 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
Agents of Disease," and yet could both have ignored all
Leeuwenhoek’s discoveries entirely. His work undoubtedly
has an important bearing on the history of both these
subjects.
Notwithstanding such present-day neglect, Leeuwenhoek’s
discoveries were utilized by contemporary theorists. I may
mention particularly Benjamin Marten,’ who published in
1720 (three years before Leeuwenhoek died) a most curious
treatise to which attention has recently been directed by Singer
(1911). In this book Marten, by assuming that tuberculosis
is caused by invisible “ animalcula”’ like those discovered by
Leeuwenhoek, develops a theory of the pathogenesis of this
disease remarkably similar to current conceptions. In many a
passage, if one substitutes “ Bacillus tuberculosis” for
“animalcula”’ his statements are in close agreement with the
views expressed in modern bacteriological and pathological
works. As a prognostication, or even as a mere tour de force,
Marten’s book is notable: but he himself never saw the
tubercle bacillus, and his writings had no influence on the
history of bacteriology.
In recent times a claim to recognition has also been made
for the French physician J.-B. Goiffon (1658-1730), of Lyons.
Molliére (1886) calls him “wn précurseur des théories
microbiennes”’ on the strength of a dissertation on the
plague which he published in 1722. In this Goiffon
propounds the theory that plague is caused by an invisible
virus (vénin)—probably some kind of “insect” “—which floats
in the air and penetrates into the blood either through the
pores of the skin or else through the mouth or nose. But
Goiffon never attempted to see such “insects” himself, and
makes no mention of the real “animalcules”’ already well
known at that date (through the discoveries of Leeuwenhoek
1 Grober (1912). This German writer’s ignorance of L.’s existence was
possibly feigned, and due to a false patriotism: for though his book bears
evidence of considerable learning, its author had apparently never even
heard of Pasteur also.
2 Marten was a London physician about whom very little seems to be
known. His book is excessively rare, and I am indebted to Dr Charles
Singer for the loan of his own copy—the only one which I have studied.
There is another, however, in the British Museum.
3 Tn one place he actually conceives of it as possessing wings !
THE ENVOY o1D
and his imitators). His own speculations are not particularly
prescient or original, and appear to have but little relation
to modern conceptions. I regard Goiffon’s dissertation as
historically negligible: in any case, it was without influence
upon the course of bacteriology or protozoology.
I cannot omit to mention, in the present connexion, an
extraordinary effort in pseudo-microbiology published just
after Leeuwenhoek’s death by a French quack doctor. This
charlatan, who wrote under the initials ‘““ M.A.C.D.”, pretended
to discover the “insects” responsible for all diseases, and to
cure his patients by eradicating them by secret methods.’
He claimed to be following the system of an English physician
who had learned of it in Persia: and he gave a comical
description—accompanied by the crudest cuts—of no less than
91 absurdly-named “little insects” which cause as many
complaints. This imposture was exposed by Vallisneri,” in a
posthumously published letter which is not generally known.
I need make no further reference to it: I mention it only
because certain learned authors have apparently taken this
obvious bit of charlatanry for a serious contribution to
microbiology or for genuine satire.’ It was certainly neither.
There is no need, for present purposes, to trace in detail
the history of our knowledge of Leeuwenhoek’s “little
animals’? down to modern times. We are here concerned
merely with the beginnings of protozoology and bacteriology :
yet to see them as beginnings we must cast our eye also upon
the later historical landmarks. As everyone knows, scant
progress was made in the century following Leeuwenhoek’s
death; though it is worth noting that the first scientific
1 See M.A.C.D. (1726, 1727). I quote him (as is customary) under
these initials, though his real name, according to Vallisneri (1733), was Boil.
From the “ Privilége du Roy” at the end of his work, where the author
is referred to as ‘le siewr A.C.D.’, it seems that the initial M. stands
for Monsieur. Consequently, he ought properly to be catalogued as
Pa ey ag
“See Vallisneri (1733), Vol. III, p. 218. It is here explained how “Mr
A. C. D.’ was able to impose upon his patients by showing them the
“insects”? in their blood or urine through a trick microscope—which
apparently exhibited the object mounted before it, but really showed
protozoa out of an infusion.
* Cf. Lesser (1738), Ehrenberg (1838), Bulloch (1930), ete.
ce
376 LEEUWENHOEK AND HIS “‘ LITTLE ANIMALS”
names' were assigned to protozoa by John Hill’ in 1752, and
that the first serious systematic treatment of both protozoa
and bacteria was attempted in 1773 by O. F. Miiller*—
revising and amplifying the inadequate account of these
organisms given by Linnaeus* (1758, 1767). These three
writers—an Englishman, a Dane, and a Swede—were all very
remarkable men, in very different ways; yet they had this in
common that they all respected Leeuwenhoek. Even the
cavalier Hill—a bitter critic of the Royal Society and all its
works (which he nevertheless copied’ freely for his own
profit)—was forced to allow his merits. In one place he says,
for example, “Even Lewenhoeck the Father, as he may be
called, of this Branch of Observation, is not without his
Mistakes, tho’ there are many more in Proportion in all
that have followed him”.°
Hill was an amateur microscopist, and he made no original
contributions of value to protozoology: but though Linné
was a professional naturalist, he had equally little know-
ledge of the Protozoa—notwithstanding he made the first
attempt to classify the micro-organisms known in his day.
But Miller was a systematist with a good working knowledge
of the “‘ Infusoria.”‘ He applied Linné’s system to organisms
which he had himself seen and studied: and he was, withal, an
1 They were pre-Linnaean and not binominal: yet some of them—such
as Paramecium—are still current.
2 Much has already been written about ‘Sir’? John Hill (1716-1775),
though nobody has yet duly appraised his contributions to protozoology.
Cf. especially the Dict. Nat. Biogr., T. G. Hill (1913), and Woodruff (1926).
* Otto Friderich Miiller (1730-1784). Cf. Dansk Biogr. Lewx., XI, 594.
The most recent estimate of him (chiefly as a botanist) is that of Christensen
(1922, 1924). Biitschli fully appreciated his protozoological works, but no
other recent student of the protozoa has attempted to assess or even interpret
all his extremely important observations on these organisms.
* Carl von Linné (1707-1778). For his life see especially Daydon
Jackson (1923).
° As an instance I may note that most of Hill’s figures of protozoa
(1752) were boldly copied without acknowledgement from the anonymous
writer of 1703—from the Phil. Trans. which he so affected to despise !
® Hill (1752a), p. 94.
" Miiller’s “ Animalcula Infusoria”’ were a motley crew of microscopic
creatures, comprising not only all the protozoa and bacteria then known,
but also worms, rotifers, algae, and other organisms.
THE ENVOY S17
excellent observer. His wrong interpretations were inevitable
at the time when he wrote: and when we remember that he
made his observations mostly with the aid of simple lenses of
English manufacture (probably much inferior to Leeuwenhoek’s),
we can now only admire his accuracy. In my view, Miller was
one of the great protozoologists of all time. He was also, for
his period, a good bacteriologist—familiar at first hand with
many bacteria—though he nowhere considers the possibility
that any micro-organisms may be causally connected with
disease.
Linnaeus’s views regarding protozoa and bacteria, and their
relation to infectious diseases, are not easily ascertained.
In the Systema Naturae (ed. X, 1758) he grouped all the
known protozoa in his Class VERMHES and its last order
ZoopHyTa. Apart from a few Foraminifera and Vorti-
cellidae—placed under molluscs and polyps respectively—all
the Protozoa which he recognized were comprised in the single
genus Volvox, containing only two species. In his 12th
edition, however, he elaborates this system somewhat, and
assigns all the “ animalcules” then known to three ill-defined
genera—Volvox, Furia, Chaos. All the “ infusoria”’ described
in “the books of micrographers” (including Leeuwenhoek)
are lumped together in a single species ‘“ Chaos infusorium”’ :
but as an appendix he adds 6 doubtful kinds of “living
molecules ”’ which he leaves to his followers to elucidate." The
list 1s so curious, in many ways, that I must quote it here: ?
The contagion of eruptive fevers ?
The cause of paroxysmal fevers ?
The moist virus of syphilis ?
Leeuwwenhoek’s spermatic animalcules ?
The aery mist floating in the month of blossoming ?*
Miinchhausen’s septic agent of fermentation and
putrefaction ?
wine Os" "G8
Dr Bulloch—who quotes the foregoing list in its original
1“ obscurae . . . moleculae vivae . . . posteris relinquendae.”
2 I translate the original Latin into English in order to be consistent :
but all students of the history of protozoology and bacteriology are doubtless
familiar with Linné’s own words.
3 Meaning, of course, the month of May—which the Dutch also prettily
call Bloeimaand.
“ce
378 LEEUWENHOEK AND HIS “LITTLE ANIMALS”’
Latin—justly remarks (1930, p. 22) that it “is surprising to
find Linné, 30 years after Leeuwenhoek’s death, placing in
the same class spermatozoa and the ‘ethereal clouds in the
time of flowering’’’; and he and others have been puzzled by
Linné’s “ aethereus nimbus”’ (e, supra). But it is probably, I
think, merely a reference to the anonymous English author
of 1677."
Linnaeus himself doubted whether all the then known
protozoa” and bacteria (as we now call them) might not really
be stages in the development of fungi, and he questioned their
relation to diseases. Similar vague suggestions were mooted
in the dissertations of some of his pupils (Bostrém, 1757;
Nyander, 1757; Roos, 1767): but what Linnaeus himself
believed I cannot discover. I think he had no definite ideas ;
for though he was certainly not blind to the possibility that
‘“microbes’”’? may cause diseases, he was also sceptical and
unable to make up his mind. In his own thesis for his degree
(1735) he argued that “intermittent fevers” are caused by
drinking water contaminated with clay, though in 1757 he
apparently approved Bostrém’s thesis contending that the
cause was “bad air” or faulty sanitation. Yet at the same
time he envisaged the existence of “exanthemata viva”
(cf. Nyander), and ten years later (cf. Syst. Nat., and Roos,
1767) was seemingly still sitting on the fence. In my view,
Linné and his pupils never understood Leeuwenhoek’s “ little
animals,’ and all their attempts at systematization merely
created confusion. ‘Their works are of great historic interest,
however, in showing how far professional biologists and medicos
had profited by Leeuwenhoek’s “amateur” labours a century
after he announced his first discoveries.
The only other authors of this period who call for passing
notice here are three Germans—of very different merits. First,
Résel von Rosenhof,’ a miniature-painter who published some
admirable descriptions and figures of protozoa in 1755: secondly,
1 Quoted on p. 373 supra.
2 The name “ Protozoa” was first used by Goldfuss (1817): but his
group so named included not only the “ Infusoria” but also “ Lithozoa”’,
’
‘“ Phytozoa’’, and “ Medusae”’.
3 August Johann Résel von Rosenhof (1705-1759). His life by Kleemann,
his son-in-law, is prefixed to the fourth volume of his Insecten-Belustigungen.
Cf. also Miall (1912), p. 293 sq.
THE ENVOY 379
Ledermiiller,’ a lawyer and amateur microscopist: thirdly, the
physician Wrisberg°— better known as an anatomist and
obstetrician—who published a dissertation on ‘“ Animalcula
Infusoria” in 1765. The work of Ledermiiller (1760-1765) is
really almost negligible, so far as the Protozoa are concerned.
It is chiefly remarkable for being constantly misquoted as the
first publication in which the indefinite term “ Infusoria ” was
employed*: but so far as I have been able to discover, the
word occurs nowhere in Ledermiiller’s long-winded writings.
It was really first used, I believe, by Wrisberg in the booklet
just mentioned, which—though always cited as a classic—
contains little of protozoological importance or novelty.
The much-quoted English works of Adams* (1746) and
Baker ° (1742, 1743, 1753, etc.) are of no account. Both were
copyists and compilers, who drew largely upon Leeuwenhoek’s
publications for their own purposes. Baker’s books, however,
enjoyed a great vogue among the amateurs of his day, and
were translated into several foreign languages. In the opinion
of Harting (1876)—which seems well founded—the Dutch
translations of his popular works on the microscope were,
indeed, responsible for a sudden revival of interest in Leeuwen-
hoek in Holland: for it is a singular fact that on his death
Leeuwenhoek was not only almost immediately forgotten by
the learned world but even by his own countrymen, and the
memory of his achievements has therefore undergone periodic
-resuscitations both at home and abroad.
The latter half of the XVIII Century was enlivened by
the classical controversy between Spallanzani® and Needham
—
1 Martin Frobenius Ledermiiller (1719-1769). For his life see the
recent sketches by Willnau (1921, 1926).
* Heinrich August Wrisberg (1739-1808). His life will be found in the
Allg. Dtsch. Biogr. and Hirsch’s Lexikon.
* Biitschli—usually so accurate—appears to be responsible for the origin
of this erroneous statement. Ledermiiller actually spoke only of “infusion
animalcules”’ in the vernacular (“Infussions Thierlein”; op. cit. Vol. I,
p. 88).
* George Adams, the elder (?-1773) : mathematical instrument-maker to
George III. See Dict. Nat. Biogr.
° Henry Baker, F.R.S. See note 1 on p. 318 supra.
° The Abate Lazzaro Spallanzani (1729-1799)—too great and famous an
ornament of Italian science to require annotation here. (But the reader
may consult with profit the recent note by Bulloch, 1922.)
380 LEEUWENHOEK AND HIs “LITTLE ANIMALS”
(supported by Buffon)' on the subject of spontaneous generation.
This dispute is too familiar for reconsideration here: and
I need only note that Spallanzani successfully defended
Leeuwenhoek’s position—though he paid little attention to
his Dutch predecessor—and was able to support their mutual
belief by many admirable new experiments. But despite his
great experimental skill and instinctive appreciation of scientific
principles, Spallanzani possessed no real knowledge of protozoa
or bacteria. Most of the organisms which he studied can now
be recognized only with difficulty, or not at all, from his
descriptions. Spallanzani was a great experimentalist and
physiologist, but no morphologist or systematist. Needham’s
contributions, however, to all branches of protozoology and
bacteriology may not unfairly be now assessed as nil. He
may have been a good Catholic, but he was a hopelessly bad
protozoologist and bacteriologist.
Although the middle of the XVIII Century produced
numerous confirmations of Leeuwenhoek’s protozoological
discoveries, they were not—at that time—usually so regarded:
they were rather considered as novelties. Nevertheless,
Antony’s marvellous researches on the multiplication of
Volvox and other phytoflagellates were extended by the work
of Trembley’ (1744a, 1747), de Saussure * (1769), Ellis * (1769),
and Corti’ (1774)—two Genevese, an Englishman, and an
Italian. Germany, soon afterwards, also contributed her
share to protozoology through the work of Gleichen* (1778),
? John Turberville Needham (1713-1781), a British catholic priest who
spent most of his life in France and Belgium. Elected F.R.S. in 1747.
2 Abraham Trembley (1700-1784), sometime tutor to the sons of
William Bentinck, English resident at The Hague. Later he came to
England, and was elected F.R.S. in 1743.
3 Horace Bénédict de Saussure [sew Desaussure ] (1740-1799), naturalist
and celebrated Alpinist. For his life see especially Senebier (1801). He
was elected F.R.S. in 1788.
* John Ellis (1710 ?-1776), government agent in the West Indies, and
author of the well-known work on Corallines. Elected F.R.S. in 1754.
* Bonaventura Corti (1729-1813), a catholic priest. Professor of
Natural History at Reggio, and a friend of Spallanzani. One of the earliest
students of the Cyanophyceae, and the discoverer of Spirulina.
* Baron Wilhelm Friedrich von Gleichen-Russworm (1717-1783).
THE ENVOY 381
who re-examined the organisms in infusions, and of Eichhorn '
(1775, 1783), who discovered the first heliozoon (Actino-
sphaerium). But Holland’s only representatives during this
period were Job Baster (1759), who recorded some trifling
observations on vorticellids, and Martinus Slabber (1778) who
rediscovered, redescribed, and first depicted Noctiluca.” Yet
it is a remarkable fact that—apart from Miiller, who was in
this connexion mainly a nomenclator and systematist—
nobody arose anywhere for more than a century following
Leeuwenhoek’s death who can now fairly be called a bacterio-
logist. For 150 years from the date of their discovery
the Bacteria were strangely neglected. Mankind remained
inexplicably blind to their importance, and almost to their
very existence.
From the standpoint of protozoology and bacteriology the
first quarter of last century is a blank. At the end of this
barren period, however, a revival of interest in Leeuwenhoek’s
“little animals” set in—a revival which led, with gradually
increasing momentum, to the enthusiastic development of our
modern sciences. It is now difficult to place oneself in the
position of a zoologist or physician a hundred years ago:
progress in our knowledge of all “ microbes’ has since been so
rapid and so revolutionary. In 1832, Bory de St.- Vincent * had
just published his reclassification of the “ Infusoria ”—which
he needlessly renamed ‘‘ Microscopica’’ *—and Ehrenberg’ was
busy cataloguing the booty collected in his travels: his
monumental monographs were just germinating in the form of
1 Johann Conrad Hichhorn (1718-1790), pastor of the Church of
St Catharine at Danzig.
2 Noctiluca, one of the chief organisms causing phosphorescence on the
surface of the sea, was discovered by the Englishman Joseph Sparshall,
of Wells in Norfolk, whose observations were recorded by Baker (1753,
p. 402 sq.).
* Colonel J. B. Bory de St.-Vincent (1778-1846), soldier, politician,
traveller, and naturalist. For his life, works, and correspondence see
Lauzun (1908).
4 “ Microscopiques.” I believe Bory borrowed this term—as he did so
much else—from Miiller (1773, p. 4: “microscopica dicuntur, quod unice
lenticulae amplificantis ope videntur’’).
° Christian Gottfried Ehrenberg (1795-1876), of Berlin. The fullest
biography is that of Laue (1895). See Dobell (1923a) for further references.
382 LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
tentative preliminary papers.’ His huge final treatise of 1838,
together with its comparatively small but devastating corrective
by Dujardin’ in 1841, forms the real foundation of modern
Protozoology. But the first experimental work on trans-
missible microbic diseases was probably that published in the
same period by Bassi * (1835), while the first on any protozoal
infection came much later from Pasteur (1870). Both of these
experimenters studied, singularly enough, no well-known
maladies of man, but certain obscure “epidemics” of silk-
worms—“ moscardino”’ and “ pébrine”’ respectively.’
It is not my purpose now to trace the history of Proto-
zoology and Bacteriology during the last hundred years, so I
shall leave the subject at the moment when our modern sciences
commenced. The authors I have mentioned, and the works
which they performed, are chronicled merely to remind the
reader of certain salient events which cannot be overlooked if
we would see Leeuwenhoek in his true perspective and
proportions.
Of Leeuwenhoek’s discoveries in sciences other than
Protistology I am not competent to speak. I observe, however,
that he is usually most praised by those most qualified to judge.
Those authors who decry his observations generally reveal
themselves, at the same time, ignorant of himself and his
works. Asan instance I may cite the opinions expressed by
certain botanical writers. Two careful Dutch authors—
van Hall (1834) and Bolsius (1903)—find much that is original
and admirable in Leeuwenhoek’s studies of plants: but the
more famous German botanist Sachs (1875), whose knowledge
of Leeuwenhoek was obviously not profound, says that “
the whole, all his numerous communications, in comparison
1 T possess and have studied all of these, though I do not cite them here.
2 Félix Dujardin (1801-1860), Professor of Zoology at Rennes. For his
life see Joubin (1901). I have also studied—though I do not cite—the
earlier works of this admirable protozoologist.
® Agostino Bassi (1773-1856), of Lodi. See his Opere (1925), recently
reprinted and edited, with a remarkable introduction by the late Prof.
B. Grassi; who sums up his review with the statement that “it is proved
that parasitology, like many other branches of knowledge, had its cradle
in our own Italy: foreigners have merely recognized and perfected it.”
Nevertheless, no Italian saw protozoa or bacteria before the year 1674.
* Moscardino is now supposed to be caused by a fungus (Botrytis) and
pébrine by a protozoon (Nosema)—both of doubtful systematic status.
THE ENVOY 383
with Malpighi’s pleasing clarity and Grew’s systematic
thoroughness, create a painful impression of superficiality
and amateurishness.””* A similar opinion of Leeuwenhoek’s
work in general has, moreover, been recently expressed by one
of his own compatriots (Becking, 1924), who sees in him
merely “a pair of eyes, a pair of hands, directed by other
minds. For when his own mind tried to direct, he could
produce nothing but chaos.” ‘This is surely a strange estimate
of the almost wilfully independent Leeuwenhoek I know—who
certainly produced something very different from chaos when
he discovered the Protozoa and the Bacteria! But even for
these discoveries Becking allows Leeuwenhoek little credit: he
avers that “although he was the first to see bacteria, yeasts
and protozoa, we can not look upon him as the founder of
microbiology.” Despite his obviously great knowledge’ of
Leeuwenhoek, and his own distinction in other branches of
learning, I am unable to judge of Becking’s competence in
protozoology—since he has not (to my knowledge) contributed
as yet anything to the advancement of that science. His
evaluation of Leeuwenhoek may, however, be contrasted with
that of the only man of our times who possessed a profound
knowledge both of the Protozoa themselves and of proto-
zoological history. He not only respected and admired
Leeuwenhoek’s work, but he even dedicated one of his own
most important memoirs to his memory.”
Other biologists have already honoured Leeuwenhoek in
their own peculiar way by naming various organisms after him.
It is true no protozoon or bacterium or other “little animal ”
1 Sachs (1875), p. 264; translated. I have good reasons for believing
that these words were actually plagiarized from an earlier and less-known
author.
2 Becking writes as one who knows all about L., and he says that “ the
uncritical praise of his commentators and biographers can only be ascribed
to an insufficient knowledge of his works and that of his contemporaries.”
Considering Becking’s greater knowledge, I confess that at first I found it
difficult to understand how he could refer to L. as “a humble lens-grinder ”’,
who was ‘a patrician’s son”? and “had many children’’, ete. But such
obvious misstatements of fact are to be explained, doubtless, by his con-
viction that “What really matters in a biography is not the so-called
biographical datum.”’ I differ from him in believing that accurate data are
the szne qua non of any biography.
3 Biitschli (1876).
384 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
of his own discovering now bears his name:’ yet it has been
bestowed—more or less permanently—upon a minute moth,’ a
tiny mite,’ and an insignificant Australian flowering plant* .. .
“cum rerum Natura nusquam magis quam wm minimis
tota sit.”
My personal estimate of Leeuwenhoek is based upon a
study of his own works. [admit that [have not yet examined
his numerous writings sufficiently, but I have read enough to
realize that those people who ridicule him are generally
ignorant, and usually reveal their own incompetence in the
very act of denouncing his. Whilst professing to show us his
faults they unintentionally pillory themselves. Leeuwenhoek
and his disciples have now no need even to contradict state-
ments such as “this physician described many things that he
never saw,’ or “his assertions . . . sufficiently prove that
he saw less through his microscope with his eyes than with
his imagination:’’’? and nowadays we only laugh when we
read this pronouncement by the self-appointed judge of the
Royal Society—*‘ Lewenhoeck . . . had the good fortune
to be one of the first People who worked at microscopical
Observations, but we are to acknowledge at the same Time,
that he has had the Honour of having stocked the Philo-
sophical Transactions with more Errors than any one Member
of it, excepting only his Successor in Peeping, Mr. Baker.” °
1 The name “ Pandorina leuwenhoekii’’, proposed by Bory de St-Vincent
(1826, p. 22), is an invalid synonym of Volvox globator Linnaeus: while the
same author’s ‘‘ Esechielina lewwenhoekii”’ (1826, p. 78) has been engulfed
in the synonymy of Rotifer vulgaris.
2 Oecophora leeuwenhoekella [Tineidae] F. v. P. Schrank, 1802. For
the various spellings of the specific name see Sherborn (1927). Cf. also Isis
(1839), p. 192.
3 Genus Leewwenhoekia Oudemans, 1911.
4 Levenhookia pusilla Brown, 1810. In proposing the genus, Robert
Brown says (in Latin) that he dedicates it ‘to the memory of the most
famous micrographer, in whose works there are many most beautiful
observations on the structure of vegetables.” Brown’s spelling of the
generic name is curious, and is evidently an attempt to reconcile Dutch
orthography with Latin and with English pronunciation. Later emendations
(such as ‘‘Leevenhokia’”’ van Hall, 1834) can hardly be regarded as
improvements.
° Jourdan (1822), Biogr. Méd., V, 561.
® John Hill (1751), p. 156. The reference is to Henry Baker (see
p. 318 supra), one of Hill’s pet aversions.
THE ENVOY 385
At all times the name of Leeuwenhoek has been mentioned
with respect by those who have really made his acquaintance.
Even general historical writers’ are sometimes aware that he
was one of the phaenomena of the XVII Century: and even
in his own lifetime his claims to recognition were conceded by
biological and medical authors. Leeuwenhoek was no
‘physician ” or “ surgeon ’’, as he has so often been ridiculously
styled: nevertheless, he was already called “celebrated” in
Roukema’s Dictionary of Famous Physicians as early as 1706,
and he now has a whole section to himself in Banga’s History
of Medicine and its Practitioners in Holland (1868) and in
Hirsch’s Biographical Lexicon of Distinguished Doctors of all
Times and Peoples (1886). The great and learned Leibniz
paid attention to his discoveries, which were not without
influence upon his own philosophy: indeed, the abstract
‘““monads”’ of the Monadology are not altogether unrelated to
Leeuwenhoek’s concrete “animalcules”.” But to trace
Leeuwenhoek himself through all the misunderstandings and
misquotations and muddles of the multitudinous authors who
have utilized his discoveries for their own ends, is a task
beyond my competence; and for my present purpose it is,
fortunately, unnecessary.
Leeuwenhoek will be finally judged by his own writings,
and not by anything that other people say he wrote. He has left
us a great mass of records—both published and unpublished
from which we can now extract what we please. I have
endeavoured to recover from them all his observations on the
Protozoa and the Bacteria, and to set in order his inchoate and
uncorrelated findings in a manner which may fairly convey
their import and importance to present-day students. ‘To me
his words, when judicially weighed in the scales of con-
temporary and recent knowledge, prove conclusively that he
was the first protozoologist and the first bacteriologist. He
has had thousands of followers and imitators, and was pre-
ceded by a few prophetic precursors; but his own true place
in Protozoology and Bacteriology appears to me incontro-
1 For example, Hallam in his Literatwre of Europe (published first in
1837-9).
2 Leibniz also mentions L. in his Théodicée (published in 1710). His
correspondence with L. is discussed by Ehrenberg (1845): but the first author
who appears to have realized Leibniz’s intellectual debt to L. is Radl (1905).
25
386 LEEUWENHOEK AND HIS “LITTLE ANIMALS”’
vertible. He was the originator of everything we now know
about ‘‘ microbes ’’, and of all that will ever be known about
these organisms. To say that he is “not the founder of
microbiology . . . although he was the first to see bacteria,
yeasts, and protozoa”? may sound very knowing, and may
satisfy those who seek paradox and literary effect: but every
workaday bacteriologist and protozoologist knows that it is
sheer nonsense. One might equally well say that Columbus
did not discover the New World because he left no account of
New York.
In the foregoing pages I have done my best to portray
Leeuwenhoek and to chronicle some of his great discoveries
anew in his own words. If I have also attempted to represent
other leading figures in the historic scene wherein he himself
appears, it is because I realize that he can be recognized in
his true character only when the other actors are ranged
beside him on the stage. It is not for me, or any other living
man, to design or paint the scenery or to dress the players or
even to clap or hiss their exits and their entrances. I can
but strive to discharge with fidelity the humbler office of the
man who manipulates the limelight—whose duty is to show,
in just illumination, the performers in a drama which I neither
did nor ever could compose, and of whose intricate plot I have
but the roughest working knowledge.
I have always endeavoured to regard Leeuwenhoek
objectively and dispassionately, but I am conscious that I
have not always succeeded: for whenever I listen to his talk
about “little animals” I am carried away by the unintentional
eloquence of his discourse. He speaks an ungrammatical and
old-fashioned language which is not my mother-tongue, and
which I have learned painfully and as yet imperfectly : but he
also echoes a language which I hear oftener than any other—
that of the “little animals” themselves. I have spent all my
working life trying to understand them, but I still know no
more than old Antony knew—just enough, in fact, to inspire
me with the enthusiasm to continue listening and labouring,
but never enough to feel satisfied with my interpretations.
I have unbounded admiration for Leeuwenhoek because he
heard and interpreted things that I, unaided, could never have
discovered, and hit on problems—during quiet nights in his
own private closet—of which neither he nor I can ever know
the final solution.
THE ENVOY 387
One of Leeuwenhoek’s own countrymen has recently called
me his “ greatest living admirer.”* I am proud to admit the
accusation, and this book gives some of the grounds for my
conceit. But the foregoing pages are not meant as an appeal
to the reader’s emotions—only to his reason. “ How Dogma-
tical soever my Assertions may seem to be, yet do I not affect
the unreasonable T'yranny of obtruding upon the Faith of any.
He that speaketh Reason, may be rather satisfied, in being
understood, than believed.” ” Consequently, if my poor labours
succeed in robbing me of a title which I hold but temporarily
and precariously, they will not have been wholly in vain; and
I shall be the first to rejoice when I am deposed from a
position which I do not deserve, cannot maintain, and have
never sought.
As I aim at nothing but Truth, and, so far as in me
lieth, to point out Mistakes that may have crept into
certain Matters; I hope that in so doing those I chance
to censure will not take it ill: and if they would expose
any Errors in my own Discoveries, I’d esteem it a
Service; all the more, because ’twould thereby give me
Encouragement towards the Attaining of a_ nicer
Accuracy.”
1 Dr W. H. van Seters, as reported in the Nieuwe Rotterdamsche Courant
of 13 July 1926 (Nr. 83, blz. 6).
2 Nehemiah Grew (1672), last lines of Preface.
* Translated from L.’s Letter 135 (25 Dec. 1700): published in Brieven,
Sevende Vervolg, p. 307.
388
A SHORT LIST OF LEEUWENHOEK’S WRITINGS
HERE is still no complete edition of all Leeuwenhoek’s
letters: and of those already published there are so
many versions that specific reference to any particular
passage is often a matter of grievous difficulty. The biblio-
graphies already printed by Gronovius (1760), Pritzel (1872),
and many others, are so incomplete and otherwise imperfect
as to be almost worthless. But a committee of experts has
lately been formed in Holland with the object of printing or
reprinting all Leeuwenhoek’s extant writings; and we may
therefore hope that the material for a full and accurate biblio-
graphy will shortly be collected and collated, and placed at the
disposal of the public.
In the meantime, since I have not the leisure or learning
—still less the funds—of the Dutch committee, but owe it to
my readers to give the sources of my own information, I can
only offer the following record of those writings which I have
myself consulted. For the present work I have had to study
every available manuscript and publication in order to collect
the passages relating to protozoa and bacteria, and I have
therefore had to catalogue every discoverable letter and collate
all its versions. But my own private list of Leeuwenhoek’s
writings, so compiled, is still far too faulty to print here—and
also far too long: and moreover this is obviously not the place
to publish such a compilation. I therefore give now only the
briefest indication of my sources for the assistance of fellow-
students.
MANUSCRIPTS
The Leeuwenhoek Manuscripts in the possession of the Royal
Society: 4 volumes, containing also numerous translations,
drawings, and other relevant material. Lmperfectly catalogued
by Halliwell-Phillipps (1840). Referred to, here throughout,
as ‘ Roy. Soc. MSS.” Together with a few letters among the
Boyle MSS. and elsewhere in the Society’s archives, and
LEEUWENHOEK’S WRITINGS 389
including fragments and copies of letters addressed to others,
they amount approximately to 200. At present I cannot
enumerate them more exactly. (Their number is grossly
overstated by most previous authors, who apparently count
originals and translations and printed proofsheets as “ original
manuscripts.) As these manuscripts form the basis of the
present work, I may add the following notes upon them:
The Roy. Soc. MSS. (mostly Dutch) were very incompletely
and imperfectly printed in the form of extracts or abstracts,
in English or Latin, in contemporary numbers of the Philo-
sophical Transactions and Hooke’s Philosophical Collections
(which replaced the Transactions between Vol. XII, 1678-9,
and Vol. XIII, 1682-3). These periodicals contain approxi-
mately 120 printed “ extracts’ from Leeuwenhoek’s letters,
though the “extracts” do not represent exactly the same
number of original letters. The printed versions will all be
found in Phil. Trans. Vol. VIII (1673) to Vol. XXXII (1723)
inclusive [none in Vols. XVI and XXX], and are indexed—
more or less accurately—by Maty (1787). Similar “ extracts”
from 2 letters were included in Hooke’s Lectures and Collections
(1678)—reprinted in his Lectiones Cutlerianae (1679)—and of
3 others in his posthumous Philosophical Haperiments and
Observations edited by Derham (1726).
Many of these manuscripts were published in full, however,
in Leeuwenhoek’s printed Dutch and Latin collective works,
and 14 of the previously wholly unpublished early Dutch
letters have just appeared in Opuscula Selecta Neerlandicorum,
Vol. IX (1931): while two of the letters sent to the Royal
Society, together with a fragment of Letter 116, have passed
somewhat mysteriously into the Sloane MSS. now preserved
in the British Museum. (I say ‘mysteriously’ because the
honourable Sir Hans Sloane, M.D., had no obvious right to
incorporate any of Leeuwenhoek’s original letters, addressed
to him as Secretary of the Society, in his own private
collection.)
Other surviving manuscripts of Leeuwenhoek are known to
me only through more or less recently printed versions or
descriptions. I have not yet been able to study all the
originals, but note their existence here for the help of others:
The Leeuwenhoek Manuscripts in the Huygens Collection at
Leyden (University Library). Eight in number, and now
printed in Guvres Complétes of Chr. Huygens (see especially
“cc
390 LEEUWENHOEK AND HIS “LITTLE ANIMALS”
Vol. VIII; 1899) or by Vandevelde and van Seters (1925).
Also partially printed or abstracted by Snelleman (1874),
Haaxman (1871, 1875), Vandevelde (1924a). [Some of the
MSS. known to Haaxman (1875) have seemingly since
disappeared. They were apparently removed by a former
librarian, who claimed them as his private property.}| A
complete list of these MSS., with 5 others (one published)
which I have not been able to trace further, is given by
Harting (1876, pp. 121-3).
The Leeuwenhoek Manuscripts in the National Library at
Florence. These letters (about 15) were all addressed to
Magliabechi,, and have been partly printed by Targioni-
Tozzetti (1745) and Carbone (1930). [The latter erroneously
includes among them a letter written by Leibniz,’ and
previously published as such by Targioni-Tozzetti (1746). ]
Four [? three] Leeuwenhoek Manuscripts in the Municipal
Museum at The Hague. They are discussed, and their contents
described, by Servaas van Rooijen (1905).
Manuscript of a Letter (dated 3 [?13] March 1716) to
Leibniz. Preserved among the Leibniz MSS. at Hanover
(fide Khrenberg, 1845), together with drafts of 3 letters from
Leibniz to Leeuwenhoek. [This letter—Send-brief XX—was
published in full in L.’s Dutch and Latin collected works. |
PUBLICATIONS
No serious attempt has yet been made by any bibliographer
to collect and collate all Leeuwenhoek’s numerous printed
letters. His published writings have been, indeed, the despair
of all authors who have had occasion to refer to them; and I’
do not, therefore, pretend to describe or enumerate all their
many versions here.
Leeuwenhoek himself published in his lifetime 165 letters
(not counting letters contained within letters): and to these
1 Antonio Magliabechi (1633-1714), a Florentine scholar of prodigious
learning. This remarkable man—of poor parentage—became librarian to
Duke Cosmo III of Tuscany: and though he published nothing during his
lifetime he is said to have been himself “ a walking library ” (including the
dust and cobwebs, apparently). L. wrote to him because he had heard that
he was then the most learned man in Italy: and he also dedicated to him
his Latin edition entitled Arcana Naturae Detecta (1695).
2 Cf. p. 46, note 1, and p. 359 supra.
LEEUWENHOEK’S WRITINGS 391
he assigned numbers—in chronological order. He published
them, however, in two separate series—the first numbered
with arabic numerals, the second with roman. But the first
series began with No. 28* (not No. 1) and ran to No. 146, and
thus consisted of 119 letters in all: while the later series
(46 letters) was consistently numbered from I to XLVI.
This, in itself, is apt to cause confusion: but the difficulty of
collation is increased because the letters were not originally
published always in strict chronological order, and were
frequently, on their first issue, not numbered at all. Their
seriation can therefore be determined only by their dates, or
by the numbers assigned to them in later issues, editions, or
translations.
All the letters originally printed in Dutch, under Leeuwen-
hoek’s supervision, were translated into Latin and printed in
that language; but the Dutch and Latin versions were not
issued simultaneously.” (As a rule—but not invariably—the
Dutch versions preceded the Latin.) Furthermore, the letters
—whether in Dutch or in Latin—generally made their appear-
ance a few at a time in the form of a brochure with a common
title: while a little later another collection would appear—
often printed for a different publisher and with a different
title—and in this some of the earlier letters were often incor-
porated. The final complete collections of Leeuwenhoek’s
letters were made up of these earlier partial collections—of
various issues—and new editions; and, in the case of the
Latin translations, sometimes of entirely new versions corrected.
and amended almost beyond recognition.
The following is a short list of the chief printed versions
—both Dutch and Latin—which I have myself been able to
study, together with a few notes [in square brackets] which
may be serviceable to others. The arrangement is chrono-
logical (for either language), and the names of publishers
are given in parenthesis after the place and date of publica-
tion. Numbers are prefixed merely for convenience of present
reference, and have no other significance.
1 Cf. p. 356 swpra, and Dobell (1931).
2 By far the best list is that given in Harting (1876, pp. 132-139): but
this publication is itself so rare that few authors can nowadays refer to it.
My own copy was most generously presented to me by the late Prof. M. W.
Beijerinck—after I had for years vainly attempted to obtain one through
booksellers.
392
LEEUWENHOEK AND HIS ‘‘ LITTLE ANIMALS ”’
I. DutcH EDITIONS
Ondervindingen en Beschouwingen der onsigtbare geschapene waarheden,
vervat in verscheydene Brieven, geschreven aan de Wijt-beroemde
Koninklijke Societett in Engeland. 4°. Leyden, 1684 (van
Gaesbeeck). [pp. viii + 8 + 32. Contains Letters 32 & 33,
unnumbered and paged separately. Figs. engraved in text.]
Ondervindingen en Beschouwingen der onsigbare geschapene waarheden,
waar in gehandeld werd vande Evyerstok [enz. enz.]. 4°. Leyden,
1684 (van Gaesbeeck). [pp. ii + 21 + 19. Contains Letters 37
& 39, unnumbered and separately paged. Figs. engraved in text.]
(a) Another edition of Letter 37 entitled: Antony van Leeuwenhoeks
37ste Missive, Geschreven aan de Heer Cristopher Wren. 4°. [Lugd.
Bat. 1696 ?] [No preliminary leaves: paged 1-20 (not 21, as in
orig. ed.), and with different make-up.]
Ondervindingen en Beschouwingen der onsigbare geschapene waarheden,
waar in gehandelt wert vande Schobbens inde Mond [enz.]. 4°.
Leyden, 1684 (van Gaesbeeck). [pp. iv + 24. Contains Letter
40: unnumbered, with figs. engraved in text.]
(a) Another edition, entitled: Antoni van Leeuwenhoeks 4Oste
Missive, Geschreven aan de Heer Francois Aston. 4°. [Lugd.
Bat. 1696 ?] [No preliminary leaves: pp. 1-24, identical with
Ist ed.]
Ondervindingen en Beschouwingen der onsigbare geschapene waarheden,
waar in gehandeld werd over het maaksel van’t Humor Cristallinus
[enz.]. 4°. Leyden, 1684 (van Gaesbeeck). [pp. ii + 26.
Contains Letter 41: unnumbered, with figs. engraved in text.]
Later edition: see No. 17.
Oniledingen en Ontdekkingen van de onsigtbare Verborgentheden ; vervat
in verscheyde Brieven, geschreven aan de Wyd-vermaarde Koninklijke
Wetenschap-soekende Societeyt tot Londen in Engeland. 4°.
Leyden, 1685 (Boutesteyn). [pp. 88, but mispaginated 79-94
from p. 72 to end. Contains Letters 38, 42, 43; unnumbered, and
with continuous pagination. All figs. engraved in text.]
(a) Another edition [? 2nd] dated 1691. [non vidi.]
(0) Another edition [? 3rd] dated 1698. Same title and publisher,
but with letters numbered.
Ontdekkingen en Ontledingen van Sout-figuren van verscheyden Souten :
van Levendige Dierkens in de Mannelyke Saden de Baarmoeder
ingestort ; ende van de Voort-telinge [enz.]. 4°. Leyden, 1685
(Boutesteyn). [pp. 76. Contains Letters 44 & 45; unnumbered,
and with continuous pagination. ]
(a) Second edition, zbid. 1696: with letters numbered (but 45 mis-
numbered 46.)
Ontledingen en Ontdekkingen van het Begin der Planten in de Zaden
van Boomen [enz.|. 4°. Leyden, 1685 (Boutesteyn). [pp. 78.
Contains Letters 46 & 47: unnumbered, and with continuous
pagination. |
(a) Another [? 2nd] edition, ibid. 1697. Letters likewise unnumbered.
LEEUWENHOEK’S WRITINGS 393
8. Oniledingen en Ontdekkingen van levende Dierkens in de Teel-deelen
van verscheyde Dieren, Vogelen en Visschen ; van het Hout met der
selver meningvuldige Vaaten [enz.]. 4°. Leyden, 1686 (Boutesteyn).
[Engraved title (dated 1685) + pp. 40 + 35. Contains Letters
28, 29, 30,31; and 34, 35, 36—each series continuously paginated
separately. Letters all unnumbered. |
(a) Second edition, 1bid. 1696. Letters numbered.
9. Ontledingen en Ontdekkingen van de Cinnaber naturalis, en Bus-poeder ;
van het maaksel van Been en Huyd {enz.|. 4°. Leyden, 1686
(Boutesteyn). [pp. 110. Contains Letters 48, 49, 50, 51, 52:
unnumbered, and with continuous pagination. |]
(a) Another edition; Leyden, 1713 (Langerack)—with letters still
unnumbered.
10. Vervolg der Brieven, geschreven aan de Wvytvermaarde Koninglijke
Societeit in Londen. 4°. Leyden, 1687 (Boutesteyn). [pp. viii
+ 155. With engraved portrait. Contains Letters 53-60: all
except the first (53) numbered, and with continuous pagination. }
(a) Second edition, ibid. 1688.
(6) Another [? 3rd] edition, zbid. 1704.
* In the preliminary pages the publisher gives a list of all L.’s letters from
No. 28 to No. 52, with their dates, publishers, titles, and contents (but not dates
of publication).
11. Den Waaragtigen Omloop des Bloeds, Als mede dat De Arterien en Venae
Gecontinueerde Bloed-vaten zijn, Klaar voor de oogen gestelt. Ver-
handelt in een Brief, geschreven aan de Koninglyke Societett tot
Londen. 4°. Delff, 1688 (Voorstad). [pp. ui (title-p.) + 1-30:
1 folding plate. Contains Letter 65 only—numbered.]
12. Natuurs Verborgentheden Ontdekt: zyjnde een Tweede Vervolg der
Brieven, geschreven aan de Koninglijke Societeit tot Londen. 4°.
Delff, 1689 (Voorstad). [pp. ii (titlepage) + 157-350 (mispaginated
after p. 260). Contains Letters 61-67, all numbered.|
(a) Second edition ; Delft, 1697 (Kroonevelt).
13. Derde Vervolg der Brieven, geschreven aan de Koninglyke Soctetett tot
Londen. 4°. Delft, 1693 (van Kroonevelt). [pp. vii + 351-
531. Contains Letters 68-75: all numbered, and continuously
paginated. |
14. Vuierde Vervolg der Brieven, geschreven aan de Wytvermaarde Konink-
lijke Societeyt in London. 4°. Delft, 1694 (van Kroonevelt).
[pp. li (titlepage) + 533-730. Contains Letters 76-83: all num-
bered, and continuously paginated. |
15. Vuijfde Vervolg der Brieven, geschreven aan verscheide Hoge Standsper-
sonen en Geleerde Luijden. 4°. Delft, 1696 (van Krooneveld).
[Engraved title (dated 1696), pp. vi + 172 + x (Blad-wyser).
Contains Letters 84-96: all numbered, and with continuous pagina-
tion. |
16. Sesde Vervolg der Brieven, geschreven aan verscheide Hooge Stands-
personen en Geleerde Luijden. 4°. Delft, 1697 (van Krooneveld).
[pp. iv + 173-342 + x (Blad-wyser & Druk-feilen). Contains
Letters 97-107: all numbered and continuously paginated.]
394
“7.
18.
LS:
20.
21.
22.
LEEUWENHOEK AND HIS “LITTLE ANIMALS”’
A. van Leeuwenhoeks 4rste Missive, Geschreven aen de Koninklijke
Societeit tot Londen [enz.]. 4°. Delft, 1698 (van Kroonevelt).
[pp. li + 26. Apart from title, and preliminary page in former,
identical with Gaesbeeck’s ed. of 1684 (No. 4).]
Sevende Vervolg der Brieven, waar in gehandelt werd, van veele Opmerkens
en verwonderens-waardige Natuurs-Geheimen. 4°. Delft, 1702
(van Krooneveld). [pp. vi + 452 + xxii (Blad-wyser). Contains
Letters 108-146 : all numbered, and continuously paginated.]
Send-Brieven, zoo aan de Hoog-edele Heeren van de Koninklyke Societeit
te Londen, als aan andere Aansienelyke en Geleerde Lieden [enz.].
4°. Delft, 1718 (Beman). [Engraved title with portrait inset
(dated 1718), pp. xiv + 460 + xxviii (Register & Druk-fouten).
Contains Letters I-XLVI, numbered and continuously paged.]
BRIEVEN [seu WERKEN]. 4°. 4 vols. (or sometimes 5). Various
dates, publishers, and places.—The final Dutch collective edition
of all L.’s published letters. Contains Letters 28-146 and I-XLVI,
and is variously made up of the several separate issues already
listed—bound together. With 2 portraits, engraved titles, and
numerous engraved figs. in text and on inserted plates. Perfect
copies, composed of first editions throughout, and with all the
plates, are now extremely rare. The following is a short description
of the only one (my own) which I have yet seen :
Deel I—Made up of Nos. 1, 2, 3, 4, 5, 6, 7, 8, 9: thus containing
Letters 28-52. With engraved title dated 1685 (1st state, with
Dutch lettering ‘“‘ Ontdeckte Onsigtbaar-heeden’’).
Deel IIT = Nos. 10, 12, 13, 14. Letters 53-83. With engraved
portrait prefixed (de Blois, after Verkolje: Ist state, with
Dutch lettering).
Deel III = Nos. 15, 16, 18. Letters 84-146. Engraved title
dated 1696 (2nd state, with Dutch lettering).
Deel IV = No. 19. Letters I-XLVI (Send-brieven), with engraved
title dated 1718 (1st state, with Dutch lettering at foot), having
Goeree’s portrait inset.
If. Latin EDItions
Anatomia et Contemplatio Nonnullorum Naturae invisibilium Secretorum
Comprehensorum Epistolis Quibusdam Scriptis ad Illustre Inclytae
Societatis Regiae Londinensis Collegium. 4°. Lugd. Batavorum,
1685 (Boutesteyn). [pp. 78. Contains Letters 43, 42, 38—in
this order—with all figs. engraved in text. Letters wnnumbered :
continuous pagination. Excessively rare first Latin edition.
My own copy is the only one which I have seen. No copy in
British Museum, or hitherto discovered in any library in Britain.]
Anatomia Seu interiora Rerum, Cum Animatarum tum Inanimarum {sic},
Ope & nebeficio [sic] exquisitissimorum Microscopiorum Detecta,
variisque experimentis demonstrata [etc.]. 4°. Lugduni Bata-
vorum, 1687 (Boutesteyn). [pp. vi + 64 (mispaginated 58) +
260 (mispaginated 258). Two parts—each continuously paged—
23.
24.
25.
26.
27.
LEEUWENHOEK’S WRITINGS 395
containing respectively Letters 43, 42, 38, and Letters 28, 29, 30,
31, 34, 35, 36, 46, 47, 44, 45, 48, 49, 50, 51, 52 (in this order).
All letters unnumbered. Figs. partly engraved in text, and partly
inserted as separate plates. With engraved title of No. 8, but
Dutch words erased. ]
A Second Issue of the preceding (No. 22) with the misprints
“inanimarum ” and “ nebeficio”’ in title corrected to inanimatarum
and beneficio. Same date, place, and publisher. [In the copy in
my possession—the only one which I have collated—the first part
(Letters 43, 42, 38) is paged 3-78, and is a reprint of these pages in
No. 21 (not 22). The mispagination of Part II is also partially
corrected. |
(a) Editio novissima, prioribus emendatior [retranslation, with letters
still unnumbered]. 4°. Lugd. Bat., 1722 (Langerak).
Continuatio Epistolarum, Datarum Ad longe Celeberrimam Regiam
Societatem Londinensem. 4°. Lugduni Batavorum, 1689 (Bou-
testein). [pp. viii (title & indices) + 124. Contains Letters 53-60,
in order; with continuous pagination but unnumbered.]
(a) Second edition ; Lugd. Bat. 1696 (Boutestein).
(0) Third edition; Lugd. Bat. 1715 (Du Vivie, Haak, & Langerack).
Letters unnumbered.
(c) Another [? 4th] edition, Lugd. Bat. 1730 (Langerak). Letters
unnumbered.
Arcana Naturae Detecta. 4°. Delphis Batavorum, 1695 (Krooneveld).
[Engraved portrait and title (same as No. 15, but with Latin
lettering and dated 1695) + pp. vi + 568 + xiv (index & emen-
danda). Contains Letters 32, 33, 37, 39, 40, 41, 61-92, with con-
tinuous pagination. Letters 32-41 unnumbered: 61-92 numbered.]
(a) Second edition ; Lugd. Bat. 1696 (Boutestein).
(0) Third edition; Lugd. Bat. 1708 (Boutestein).
(c) Editio novissima, auctior et correctior; Lugd. Bat. 1722
(Langerak).
Continuatio Arcanorum Naturae detectorum, qua continetur quicquid
hactenus ab Auctore lingua Vernacula editum, & in linguam Latinam
transfusum non fuit. 4°. Delphis Batavorum, 1697 (Kroonevelt).
[pp. i + 192 + viii (index). Contains Letters 93-107 : all numbered,
and with continuous pagination.]
(a) Reprint, with new titlepage, Lugd. Bat. 1722 (Langerak).
Epistolae ad Societatem Regiam Anglicam, et alios Illustres Viros Seu
Continuatio mirandorum Arcanorum Naturae detectorum [etc.].
4°. Lugduni Batavorum, 1719 (Langerak). [Portrait + pp. xvi
(title & index) + 429 + x (2nd index). Contains Letters 108-146,
all numbered and continuously paged. Lat. transl. of No. 18.]
Epistolae Physiologicae Super compluribus Naturae Arcants [{etc.] :
hactenus numquam editae. 4°. Delphis, 1719 (Beman). ([En-
graved title, with portrait inset (same as No. 19, but with Latin
lettering at foot, and dated 1719); pp. xx (title, dedication, &
summary) + 446 + xxvi (index & errata). Contains Letters
I-XLVI; all numbered, and paged continuously. Latin
translation of No. 19.]
396 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS ”’
29. OPERA OMNIA, seu Arcana Naturae, ope Exactissimorum Microscopiorum
Detecta, experimentis variis comprobata, Epistolis, ad varios illustres
Viros, ut et ad integram, quae Londini floret, sapientem Societatem
... datis. 4°. 4Avols. Lugduni Batavorum, 1722 (Langerak).—
This is the Latin equivalent of No. 20, and contains all the Epistolae
from 28 to 146 and I-XLVI. It is made up of various editions and
issues, and most copies which I have collated are imperfect. The
usual arrangement is as follows (though many other collections
are to be found) :
Vol. I = Nos. 23a (part i), 22 (ii), 240. [Engraved title of No. 25,
general title, and 12 other preliminary pages (carmen panegyricum,
lectort typographus, & index): pp. 1-64 + 1-260: Index triplex
[pp. xxiv]: title, pp. vi (fraemonitio ad lectorem & index) +
1-124. Contains, therefore, Letters 43, 42, 38; 28, 29, 30, 31,
34, 35, 36, 46, 47, 44, 45, 48, 49, 50, 51, 52; 53-60.]
Vol. II = Nos. 25¢ & 26a. [Engraved title of Nos. 8 & 22,
with new Latin lettering; new titlepage + pp. xiv (index)
+ 1-515; Index (pp. xxiii + errata) ; new titlepage + Index
argumentorum (pp. vill) + pp. 1-192 + Index (pp. viii). Contains,
therefore, Letters 32, 33, 37, 39, 40, 41, 61-92 ; and 93-107.]
Vol. III = No. 27. [Portrait + title with engraved device
+ pp. xiv (index 1) + pp. 1-429 + x (index 2). Containing
Letters 108-146. ]
Vol. IV = No. 28. [Containing Letters I-XLVI.]
* All these volumes contain numerous figures engraved in the text
and on large and small inserted plates—identical with those
of No. 20.
In addition to the foregoing publications, I must record the following—
issued in Leeuwenhoek’s lifetime but not by himself. [All the
original MSS. appear to be lost.]
The Letters addressed to Petrus Rabus.—Pieter Rabus (1660-1702 ;
Dutch author, poet, and critic) published in the last decade of
the XVII Century a literary review entitled ‘“‘ De Boekzaal van
Europe”’ (8°. Rotterdam). Two volumes were issued yearly—
separately paged—from 1693 to 1700: and in those published
between 1693 and 1697 Rabus not only reviewed those works
of Leeuwenhoek which appeared contemporaneously, but he
also printed several of his letters addressed to himself. As
these are not to be found elsewhere, and as they are not correctly
cited by van der Aa or others, I add exact references here. Apart
from reviews, and letters printed elsewhere, Rabus published—
more or less completely—six of L.’s letters which are otherwise
unknown. To wit: .
1. A letter dated 27 Oct. 1693. Boekzaal v. Europe 16938 (ii),
pp. 554-5. [Extract only.]
2. Letter dated 21 May 1695. Jbzd., 1695 (i), pp. 532-6.
{Extract.]
3. Letter undated. Jbid., 1695 (ii), pp. 96-9.
LEEUWENHOEK’S WRITINGS 397
4. Letter dated 10 Sept. 1695. Jbdid., 1695 (ii), pp. 258-261.
5. Letter dated 1 June 1696. Jbid., 1696 (i), pp. 522-5. [In-
complete. ]
6. Letter dated 23 July 1696. Jbid., 1696 (ii), pp. 144-151.
* There is nothing of protozoological or bacteriological importance in this otherwise
interesting correspondence.
The Letters to Magliabechi, partly published by Targioni-Tozzetti
(1745), have already been noted under “‘ Manuscripts ”’ (p. 390)—
together with several other letters more recently printed in
whole or in part.
The only extensive (though very incomplete) English Translation
of Leeuwenhoek’s works is the bowdlerized version of the Rev.
Samuel Hoole (1798, 1807), to which a fuller reference will be
found in the ensuing general bibliography (p. 410).
iby sprack oock van de boomen;
Yan den cederboom aen, die op den
Libanon ts, tot op den psop die aen
den wandt uptwast: by sprack
oock van bet vee, ende van bet
Gevogelte, ende van de Rruyppende
dieren, ende van de Visscbhen.
—I. Kon. iiij. 33.
398
OTHER REFERENCES AND SOURCES
HE following list contains all the works referred to in
ale the foregoing text, and also a number of other publica-
tions upon which I have relied for information—or
which I have had to read—but to which no specific allusion is
made elsewhere. Annotations are added where they appear
needful.
Various national and general biographical dictionaries, of
which I have naturally made considerable use, have been cited
throughout by abbreviated titles. They are as follows (other
articles or publications being given, as a rule, under their
individual author’s or editor’s name):
Allg. Dtsch. Biogr. = Allgemeine Deutsche Biographie. 8°. 56 vols. (with
supplements). Leipzig. 1875-1912.
Biogr. Ital. Ill. = Biografia degli Italiani Illustri, ed. E. de Tipaldo. 89.
10 vols. Venezia. 1834-1845.
Biogr. Méd. = Biographie Médicale: Dictionaive des Sciences médicales,
ed. A. J. L. Jourdan. 8°. 7vols. Paris. 1820-1825.
Biogr. Nat. Belg. = Biographie Nationale ... de Belgique. 8°. 22 vols.
Bruxelles. 1866-1920.
Dansk Biogr. Lex. = Dansk Biografisk Lexikon, ed. C. F. Bricka. 8°.
19 vols. Kjébenhavn. 1887-1905.
Dict. Nat. Biogr. = Dictionary of National Biography, ed. Leslie Stephen
and Sidney Lee. 8°. 70 vols. (with supplements). London &
Oxford. 1885-1927.
N. Nederl. Biogr. Woordenb. = Nieuw Nederlandsch Biografisch W oordenboek,
ed. P. C. Molhuysen, P. J. Blok, & Kossmann. 8°. 8vols. Leiden.
1911-1930.
Nouv. Biogr. Gén. = Nouvelle Biographie Générale (seu Universelle), ed.
F. Hoefer. 8°. 46 vols. Paris. 1855-1866.
AA, A. J. VAN DER (1852-1878). Biographisch Woordenboek der Nederlanden.
8°. 21 vols. Haarlem. [L. in vol. XI (1865), pp. 280-283.]
Apams, G. (1746). Muicrographia Illustrata, or the Knowledge of the
Microscope Explain’d [{etc.]. 4°. London. [L.’s observations
much quoted, and many of his figures reproduced. ]
Apams, G. (1798). Essays on the Microscope [etc.]. 2nd ed. by F.
Kanmacher. 4°. London. {Second-hand description of L.’s
“single microscope,”’ p. 7.]
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BiBii1A, dat is De gantsche H. Schrifture . . . door Last der Hoogh-Mog :
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B JORNSTAHL, es (1780-84). Resa til Frankrike, Italien, Sweitz, Tyskland,
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422 LEEUWENHOEK AND HIS “ LITTLE ANIMALS”
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423
ACKNOWLEDGEMENTS
many unexpected quests, and has brought me into
contact with so many problems and such divers people
(both living and dead), that I now find it difficult to record—
or even, I fear, to remember—all the help which I have
received from others in the course of its compilation. Almost
everybody I know has contributed—wittingly or unwittingly,
directly or indirectly—something towards its fulfilment: and
with negligible exceptions every person whose aid I have sought
has willingly furnished me with information or material. It
is impossible, therefore, to mention here by name all the
friends and colleagues, all the fellow-students and distant co-
workers whom I have never met in the flesh, all the librarians
and antiquarian booksellers and editors and publishers, who
have given me their unstinted assistance at all times. Con-
sequently, I can only beg them, one and all, to accept now
this general acknowledgement of my indebtedness.
But there are some special helpers whose names I cannot
omit to mention specifically. My debt to my two “ Brothers”
I have attempted to repay by dedicating this volume to them.
Without their fraternal encouragement it would never have
been written, and I therefore owe them both more than I can
express—big brother D’Arcy for his unattainable example
and incomparable scholarship in wider fields, little brother
Paul for his equal enthusiasm on common ground. Next
after these I would mention my old friend Mr A. Hastings
White, Librarian (now, alas! in only a consultant capacity) to
the Royal Society, whose knowledge of everything connected
with the Society has been of incalculable assistance. I have
never sought his aid in vain, and he has always placed his
own vast learning at my disposal most liberally.
I am further indebted, in no small degree, to several
good friends in Holland. That great bacteriologist, the late
i ae book has been so long a-writing, has taken me on so
424 LEEUWENHOEK AND HIS ‘“‘ LITTLE ANIMALS”
Professor M. W. Beijerinck of Delft, with characteristic
unselfishness gave me aid both material and spiritual. The
late Mr L. G. N. Bouricius, Archivist of Delft until his
untimely death on 21 February 1929, also supphed me with
much valuable information, and never failed to satisfy my
frequent inquiries to the utmost of his ability. Dr W.H. van
Seters of Leyden, who recently produced the ‘“ Leeuwenhoek
Film,” most kindly communicated—unasked—all his own
incidental findings, together with several original photographs
and a full copy of the captions. Dr E. P. Snijders—formerly
stationed in Sumatra, now Professor at Amsterdam—has given
me not only valuable advice but also a magnificent specimen
of the old Dutch Bible (1702): while Dr A. Schierbeek, at
The Hague, has rendered the kindest assistance in innumerable
ways during the last ten years. To all these unseen Dutch
friends and fellow-students of Leeuwenhoek I owe a debt
which I can never acknowledge sufficiently. They have all
given mé—a foreigner unknown to them _ personally—their
most generous help. Dr C. A. Crommelin, now Professor
of Physics at Leyden, has been equally helpful: but I
mention him separately because he is, happily, not only still
a living student and admirer of Leeuwenhoek but also one
whose hand I have actually shaken. I would also record that
the Netherlands Society of Sciences, at Haarlem, have aided
me by the gift of two important volumes of the Complete
Works of Huygens, which they are editing and publishing on
so sumptuous a scale.
Among my own countrymen who have given me continued
support I must mention particularly Professor William
Bulloch, F.R.S., and Professor F. J. Cole, F.R.S. The first—
as all real students everywhere know— possesses an unrivalled
knowledge of the history of bacteriology (and of medicine in
general): the second is now our only living authority on the
history of zoology. Both have given me the benefit of their
own solid learning on countless occasions. If I have not
profited by it, the fault is mine.
To the Council of the Royal Society I am beholden for
sranting me the facilities necessary to undertake this work ;
and to the Trustees of the National Gallery and the Directors
of the Rijks-Museum and the Mauritshuis for permission to
reproduce the pictures shown in four of my plates.
Finally, I wish to acknowledge my deep personal obligation
ACKNOWLEDGEMENTS 425
to my friend Mrs Mabel Selle, who has accurately typed the
greater part of this book: for without her expert aid I could
never have sent my original troublesome and _ repeatedly
corrected and revised manuscript to press at the appointed
hour. To my English printers and publishers, Messrs. Bale
and Danielsson, I am indebted no less: for they have invari-
ably met my tiresome typographical and other requirements
in the most sympathetic and magnanimous manner.
For mistakes I alone am responsible, and to those who
will point them out I shall ever be grateful. I have done my
best; yet I know all too well “ Het en kan niet wesen, datter
geen ergernissen en komen: doch wee hem door welcken sy
komen—It is impossible but that offences will come, but wo
unto him through whom they come” (St LUKE xvi, 1).
FINIS
426
INDEX
* This Index covers the whole of the foregoing work—text, notes, and bibliography.
It is a key to the book as a whole, and furnishes clues to all the information contained
in it—with its sources—and an indication of all the chief persons and genera of
animals and plants mentioned.
** Here, as elsewhere in all notes throughout, the abbreviation ‘“‘L.” stands for
ANTONY VAN LEEUWENHOEK.
Aa, A. J. van der 175, 396, 398
Académie des Sciences 53 sq
Acipenser 139
Actinosphaerium 381
Adams, G. (sen.) 379, 398
Adams, G. (jun.) 398
Agnew, D. C. A. 61, 399
Amsterdam 23
Amylobacter 198
Anaerobic bacteria 197 sqq
Andry, N. 399
Anguillula aceti, vide Vinegar-eel
Animalcules seu ‘ little animals ’
[=Protozoa & Bacteria}, passim
Anne, Queen 317
Anodonta 207 sqq
Anonymi auctores 399
Anthophysa 285 sqq, 343
Apprenticeship, L.’s 23
Arber, A. 168, 399
Archimedes 190
Arthrospira 110
Articles of Faith 73 sq
Astasia 164, 165
Aston, F. 47, 57, 90, 237
Astruc, J. 176, 399
Attestations, vide Testimonials
Aubrey, J. 186
Augustine, St 8
Autobiography 71
Azotobacter 198
Baan, J. van der 31, 399 |
Bacilli 133, 134, 178, 179, 245, 252 |
et alibi |
| Bacillus cola 198, 330 ; B. flexilis 236 ;
B. tuberculosis 374
Bacon, F. 183, 399
Bacon, R. 363, 364
Baen, G. 34
Baer, K. E. von 399
Baker, H. 282, 314, 318, 319, 320,
325, 326, 379, 381, 384, 400
Baker, W. E. Watson 326
Bakkenes, H. C. van 31, 400
Balantidium 229, 236
Banga, J. 31, 84, 92, 296, 385, 400
Baptism, L.’s 21
Barrow, J. 55, 400
Bassi, A. 382, 400
Baster, J. 381, 400
Baumann, E. D. 347, 400
Becking, L. B. 307, 308, 309, 327,
383, 400
‘ Bedellus immortalis ’ 33
Beelaerts, P. M. 347
Beer, H. de 313, 400
Beijerinck, M. W. 129, 178, 198,
199, 246, 353, 356, 391, 400, 424
| Bense, J. F. 12, 304, 400
Beresteijn, E. A. van 99
Bible, Dutch 4, 74, 305, 313, 400
Biddaff, J. 343
| Bidloo, G. 220, 400
Bile, globules in 217 sqq
Bill, L.’s 30
Biography 17 sqq
Birch, T. 12, 38, 40, 47, 48, 49, 57,
59; 11s, 172, 174, 176, 178; 183;
184, 185, 186, 194, 222, 231, 238,
400
INDEX
Birth, L.'s 19
Bjornstahl, J. J. 305, 400
Blanchard, E. 362, 401
Blanchard, R. 373, 401
Blankaart, S. 84, 90, 284, 401
Bleyswijck, A. van 83, 84, 88
Bleyswijck, D. van 24, 84, 401
Bleyswyk, H. van 263
Blois, A. de 349, 350
Blood-corpuscle, red 335 et alibi
Blyth, A. Wynter 32, 362, 401
Bodo 127, 132, 154
Boeke, J. 401
Boerhaave, H. 84, 270, 296, 334
otter, ac, 11, 19. 20, 23,. 24,28.
29, ol, AS, 92, 100, 102, 176,177,
301, 343, 344, 345, 360, 401
Bolnes (Vermeer), C. 35, 36
Bolsius, H. 382, 401
Bombinator 235
Bonnet, C. 401
Boogert, J. 176, 177
Borel, P. 141, 362, 364, 365, 401
Bory de St-Vincent, J. B. 381, 384,
402
Bosman, D. B. 306, 313, 402
Bostrém, A. 378, 402
Botrytis 382
Bouricwus, L.:G: N, 11, 19, 20; 21,
wea, 20,29, 30, 31, 34, 37, 99;
176, 177, 300; 30! , 302, 338, 340;
341, 353, 402, 424
Bourignon, A. 74
Boyer, J. 372, 402
Boyle, R. 39, 168, 357
Brachelius, A. 25, 402
Bray, W. 28, 406
Bredius, A. 36, 402
Brewerton, E. W. 90, 402
Bridges, J. H. 363, 402
Brocard, H. 372, 402
Brother, L.’s 18, 21
Brouncker, Viscount 182, 216, 358
Brown, R. 384, 402
Browne, T. 107, 402
Bruce, D. 356
Bruggencate, K. ten 313, 402
Bryan, M. 343, 402
Bitsenlin Oo. 221.1234 (9235... 263,
266, 298, 376, 379, 383, 402
Buffon, G. L. L. de 380
427
Bulloch, W. 78; 325, 370; 375, 377,
379, 402, 424
Bunyan, J. 72, 402
Buonanni, F. 304, 367, 371, 403
Burch, W. v. 176
Burial, L.’s 99
Burlet 54
Burnet, G. 12, 403
Bursana 164
Butterfield 116
Cabinet of microscopes, L.’s 95, 96,
97, 98, 99, 314 sqq
Camerling, J. 32
Candolle, A. De 53, 403
Cappelle, J. P. van 403
Cappelli, A. 313, 403
Carbone, D. 46, 359, 361, 390, 403
Carchesium 208, 211, 278, 285
Carswell, R. 220, 403
Carus, J. V. 403
Carutti, D. 364, 403
Castlemain, Earl of 40, 403
Catharina van Leeuwenhoek, vide
Sisters, L.’s
Cazeneuve, P. 372, 403
Celli, A. 369, 403
Cépedea, vide Opalina
Cercomonas 125, 126, 129
Cesi, F. 364
Chalk and clay 51
Chalmot, J. A. 403
Chamberlain, Sheriffs’ 31, 32
Chamberlayne, E. 270
Chamberlayne; Io 1775) 270; 271.
273,274, 275,216, 277, 278, 279;
281, 282, 283, 285, 286, 287, 288,
289, 291, 371, 403
Chantavoine, J. 36, 403
Chaos 377
Chapman, A. Chaston 363, 403
Chapman, J. 350
Charante, N. H. van 404
Charles I 19, 28
Charles II 14, 28, 184, 371
Chilodon 146, 164
| Chilomastix 224, 229, 234
Chironomus 205
Chlamydomonas 263, 264, 268, 298
Christensen, C. 376, 404
Chronological note vi
428
Chyle = Chyme 85, 284
Cicero 93, 94
Ciliary mechanism 292 sqq
Cinck, A. 80, 81, 82
Circulation-microscope 332 sq
Clove-water, animalcules in 155 sqq
Coat-of-arms, L.’s 305
Coccidia 219 sq
Cohn, F. 246, 356
Cole, F. J. 70, 184, 263, 347, 359, |
| Dispersal of animalcules by birds
404, 424
Coleps 263, 266
Colerus, J. 176, 404
Collot d’Escury 404
Colpidium 134, 135, 137, 138, 139,
140
Columella 369, 418
Comptoir, L.’s 114, 125
Conjugation of ciliates 200, 205, 206, |
213, 284
Contagium vivum 368 sqq
Cordes, H. 176, 177
Cordes, P. 176
Cornish, J. 47, 404
Corti, B. 380, 404
Cosmo III 390
Cotgrave, R. 313, 404
Cothurnia 278, 279, 280, 285
Creplin, F. C. H. 404
Crisp, F. 327, 403
Crithidia 221
Crommelin, C. A. 324, 326, 346, 404,
424
Cromwell, O. 14
Croone, W. 48, 186
Crose, J. C. dela 61 sq, 404
Cuculus 134
Cuvier, G. 404
Cyclidium 124, 125, 126, 127, 129,
133, 142, 154,955
Dale, J. H. van 313, 404
Daphma, vide Water-flea
Dark-ground illumination 331 sq
Darwin, C. 270
Daughter, L.’s,
Leeuwenhoek
Davaine, C. 404
Death, L.’s 92 sqq
Defoe, D. 318
Delfos, A. 352
vide Maria van
INDEX
Delft 24 sqq, & passim
Derham)’ Wi.) 152, 186, 222.7 389):
& vide Hooke (1726)
De Toni, G. B. 53, 404
Diatoms 278, 372
Dictionaries 312, 313
Dileptus 126, 165
Diploma of the Royal Society 48,
49, 87
Disney, A. N. 325, 327, 363, 405
270 ; by rain 163 ; by wind 267, 297
Ditch-water, animalcules in 165, 256
aed
Divini, E. 40, 41, 103
Dobell, C. 48, 217, 220, 221, 222, 224,
229, 246, 285, 356, 372, 381, 391,
405
Dods, M. 8
Drapery 23, 29, 30, 332
Draughtsmen, L.’s 147, 279, 342 sqq
Drebbel, C. 21, 363
Dryander, J. 405
Duckweed, animalcules on 276 sqq
Dudley, R., vide Leicester
Dujardin, F. 382, 405
Dutch editions 392 sqq
Dutens, L. 363, 405
Dwelling, L.’s 29, 125, 338 sqq
Edmundson, G. 12, 24, 405
Ehrenberg, C. G. 117, 278, 356, 372,
375, 381, 382, 385, 390, 405
Eichhorn, J. C. 381, 405
Eimeria 220
Elector Palatine 207, 216, 359
Elizabeth, Queen 14, 27
Elizabeth, Q. of Bohemia 28
Ellis, J. 380, 405
Elsholz, J. S. 116, 406
England, L.’s visit to 51
Erasmus 14
Esechielina leuwenhoekir 384
Euglena 111
Euplotes 142, 166
Evelyn, J. 12, 28, 39, 406
Explosion at Delft 28, 29, 55
Fabri, G. 364, 365
Fabritius, K. 28
Faille, B. de la 34
INDEX
Faith, L.’s scientific 73 sq
Family Tree 18
Fasciola 220
Father, L.’s 16, 18, 19, 20
Fellowship of Royal Society 47 sqq
Feyfer, F. M. G. de 326, 412
Film, the L. 285, 355, 424
Firmin, T. 47
Fleck, F. le Sueur 406
Fleck, J. M. 372, 406
Florio, J. 313, 406
Folkes, M. 102, 103 sq, 314, 316, 317,
318, 322, 325, 406
Fontenelle, B. de 53, 70, 71, 406
Foraminifera 51, 262, 263, 377
Foster, M. 406
Fracastoro, G. 370, 406
Frederik Hendrik 19
Frogs, animalcules in 230 sqq ;
vide Rana
Fulton, J. F. 61, 406
Funeral, L.’s 99
Fura 377
Gabb, G. H. 347
Gabler 84, 406
Gale, T. 47, 48, 49, 193, 196, 199
Galileo 363
Garden, G. 74
Garrison, F. H. 52, 368, 406
Geertruyt van Leeuwenhoek,
Sisters, L.’s
Genealogy 18
Generaal-wijkmeester 33
‘Gentleman in the Country’ 371,
399 ; vide Anonymus (1703)
George III 379
Geysbeek, P. G. W. 406
Giardia 224, 225, 229
Giesen, G. van der 102
Ginger-water, animalcules in 153 sqqg
Gleichen-Russworm, W. F. von 380,
406
Godfrey (Govert) of Lorraine 301
Godin 53, 406
Goedaert, J. 118
Goeree, J. 354 sq
Goiffon, J. B. 374 sq, 407
Goldfuss, G. A. 378, 407
Gordon, L. 176
vide
& |
429
Gordon, R. 176
| Gosch, C. C. A. 407
| Gosse, E. 43
| Govi, G. 363, 364, 407
| Graaf, R: de 39,40, 41, 42; 103, 357,
407
Grammont, vide Hamilton
Grassi, B. 382
Gray, S. 371, 407
Green, J. R. 78, 407
Gregory, D. 163, 407
eee N47 eS 16S 17279) See
186, 306, 357, 358, 367, 383, 387,
407
Grew, O. 168
Gribius, P. 93, 94, 95, 96, 97, 98, 345
_ Grober, J. 374, 407
Gronovius, L. T. 388, 407
Groot, C. H. de 62, 351, 352, 407
Gutter-water, animalcules in 165,
263 sqq
Haan, Bs 175,177
Haastert, I. van 11, 23, 31, 325, 407
Haaxman, P. A. 326, 328, 346, 407
Haaxman, Py j.eih 19) 20p 2023,
24. 27, 28, 30, 31,33) 53,004,090,
57, 70, 81, 93; 102, 115; 117; AS%
302, 305, 320, 321, 326, 335, 338,
339, 346, 347, 350, 355, 390, 408
Haaxman, S.A.(E. 328
Hadfield, R. 408
Haematococcus 263, 264, 265, 268,
269, 298
Haeser, H. 314, 408
Hairsbreadth 336 & alibi
Hake, T. G. 220, 221, 408
Halbertsma, H. 11, 20, 23, 49, 53,
54, 317, 408
Hall, H. C. van 382, 384, 408
Hallam, H. 385, 408
Haller, A. von 184, 408
Halliwell-Phillipps, J. O. 359, 388,
408
Halma, F. 312, 313, 408
Ham, J. [co-discoverer, with L.,
of spermatozoa], vide Halbertsma
(1862) & Muys
Hamilton, A. 12, 408
Hannot, S. 312, 313, 408
430
Harris, D. F. 100, 101, 409
Harris, J. 111, 371, 409
Harange, (P11, "53; 54) 320. 321.
322, 323, 324, 325, 326, 335, 338,
339, 340, 346, 350, 355, 356, 363,
364, 379, 390, 391, 409
Hartsoeker, C. 69
Hartsoeker, N. 53, 69 sg, 245, 409
Heijnsbroeck, J. 30
Heijnsbroeck, P. 30
Hein, P. 26
Hens, animalcules in 228
Henshaw, T. 186
d’Herelle, F. 356
Heugelenburg, M. 313, 409
Heusch, J.C) 47
Hexham, H. 312, 313, 409
Hill, A. 186
Hill, J. 376, 384, 409
Hill, T. G. 376, 409
Hirsch, A. 84, 92, 379, 385, 409
Hodenpijl, A. 176, 177
Hoefer, F. 409
Holmes, C. 351
Holmes, R. 33
Holt €. 371
Homer 94
Hoogvliet, A. 92
Hoogvliet, J. 90, 92, 93
Hooke, R. 43, 44, 47, 48, 49, 52,
173, 178, 182, 183, 184, 185, 186,
187, 192, 193, 194, 199, 200, 207,
221, 222, 238, 263, 308, 334, 358,
362, 364, 365, 371, 389, 409, 410
Hoole? 'S. ‘3; 90; 200; 207, 222, 231,
2371, 239, PAN, 241, 242, 247, 262.
263, 264, 266, 268, 325, 343, 350,
397, 410
Horse-fly, animalcules in 221
Hoskyns, J. 186
Houghton, J. 48
Houlatson, R. 349
House, L.’s, vide Dwelling
Howell, J. 12, 45, 307, 410
Hunt, H. 48
Huych van Leeuwenhoek, vide Uncle,
Es
Huygens, Christiaan 14, 43, 44, 50,
33, 54, 60, 70; 115; 116; 127, 128,
163 sqgq, 167, 172,177, 187; 389,
410; & vide Harting (1868)
INDEX
Huygens, Constantijn sen. 42, 43,
44, 50, 60, 115, 116, 117, 164, 167,
172, 186, 187, 192, 304, 333, 343,
347, 348, 359, 410 ; & vide Jorissen
& Worp
Huygens, Constantijn jun. 50, 60,
164
Hydra 280 sqq
Inch, L.’s 334
Incubation of cultures, first instance
of 269
‘ Infusoria ’ 377, 379
Inscriptions on L.’s tomb 100, 101
Intestinal Bacteria 222 sqq
Intestinal Protozoa 222 sq
Israéls, A. H. & Daniéls, C. E. 410
Jackson, B. Daydon 376, 410
Jacob van Leeuwenhoek, vide
Brother; L.’s
Jaeger, F. M. 21, 410
James I 43
James II 33
Jelgersma, T. 102
Jew, EE: netar22
Joblot, L3725410
Jones, W. H. S. 369, 411
Jongh, A. de, vide Junius
Jorissen, T. 411
Joubin, L. 382, 411
Jourdan, A. J. L. 384, 411
Junius, H. 24, 27, 411
Jurin, J. 88, 89, 90, 93, 94, 96, 97,
337, 411
Kaathoven, C. H. W. van 346, 347
Kaiser, L. 355, 411
Kent, W. Saville 114, 115,117, 235,
308, 326, 411
Kerkherdere, J. G. 82, 83, 223
Kerona 282, 285
Kihaan, C. 312, 313, 411
King, E. 371, 411
Kipling, R. 364
Kircher, A. 141, 162, 165 sqg, 370,
41]
Knickerbocker, W. S. 114, 411
Knipsheer, F. S. 93
INDEX
Koch, R. 348
Konarski, W. 116, 372, 411
Kruif, Paul de iii, 411, 423
Lacroze, de, vide Crose, de la
Lamblia 224
Lancisi, G. M. 369, 411
Landgrave of Hesse 60, 148
Lang, Leaf, & Myers 95
Language, L.’s 305 sqq
Last illness, L.’s 90, 91
“Last letter” to Roy. Soc. 87
Latin editions 394 sqq
Laue, M. 381, 411
Launois: P: E70, 362,411
Laurillard, E. 313, 400
Lauzun, P. 381, 411
Ledermiller, M. F. 379, 412
Leduc, S. 291, 412
Leersum, E. C. van 296, 326, 412
Leeuwen, C. van 21, 37, 412
Leeuwenhoekia 384
Leeuwenpoort 301
Leibniz, G. W. 46, 70, 71, 113, 324,
359, 360, 385, 390, 412
Leicester, Earl of 14, 27
Rely, P. 102
Lely, W. van der 102
Lemna 276
Lenses, discovery of 363; L.’s 319
ag7
Leptomonas 221
Leptothrix 246, 251, 252
Lesser, F. C. 375, 412
Letters, L.’s, vide Writings
Leuckart, R. 412
Levenhookia 384
Limnias 278
Linnaeus, C. 376 sqq, 412
Lint, J. G. de 346, 355, 412
Lipperhey, H. 363
Locke, J. 19, 186
Locy, W. A. 22, 32, 326, 347, 412
Loéffler, F. 238, 239, 246, 247, 366,
367, 370, 413
Loon, G. van 55, 80, 81, 82, 355, 413
Louse, eye of 121, 336 & alibi ;_ hair
of 337 & alibi
Louvain, medal from 79 sqq, 355
Lucaswe. V7 a6, 350; 413
Luke, St 425
431
“MA. CADy 375.435
McKerrow, R. B. 413
Maes, N. 19, 351, 353
Magliabechi, A. 46, 53, 179, 359
390, 397
Maigne d’Arnis, W. H. 313, 413
Malaria 180, 369
Malpighi, M. 168, 362, 383, 413
Man, C. de 353
Manuscripts, L.’s 388 sqq
Manzini, C. A. 40, 324, 413
Mapletoft, J. 186
Margaretha Bel van den Berch,
vide Mother, L.’s
Margriete van Leeuwenhoek, vide
Sisters, L.’s
Maria van Leeuwenhoek (L.’s daugh-
ter) 18, 28, 64, 69, 94, 95, 96, 97,
98, 99, 100, 102, 103, 240, 302, 305,
320, 361
Maria van Leeuwenhoek (L.’s sister),
vide Sisters
Marriages, L.’s 18, 28, 30, 31
Marten, B. 374, 413
Martin, B. 70, 413
Martin, T. H. 363, 413
Martinez, M. 312, 313, 413
Mary II 56, 104, 317
Matthew, St 74
Maty, P. H. 389, 413
Mayall, J. 324, 326, 327, 329, 413
Mayor, J. E. B. 413
Measurements, L.’s, vide Micrometry
Medal, the Leeuwenhoek 356; the
Louvain 79 sqq
Meerman, J. 35
Meester, W. 60
Meijer, L. 35, 114, 312, 313, 413
Melicerta 278, 279, 291, 293, 294
Memorabilia 16
Mensert, W. 364, 413
Mesmin, vide Anonymus (1679)
Mesnil, F. 53
Metcalf, M. M. 235, 413
Methods, L.’s 169 sqq, 187 sq, 200 sqq,
331 sq; & passim
Mey, Barbara de 16, 18, 28, 30
Mey, Elias de 28
Miall, L. C. 87, 263, 378, 414
Micrococci 245
Micrometry, L.’s 200 sqq, 333 sqq
432
Microscope, discovery of 363
‘Microscopes,’ L.’s 96, 97, 98, 103,
313 sqq
Microscopica 381
Miller, W. D. 245, 246, 414
Millet-seed 335 sq; & alibi
Minsheu, J. 312, 313, 414
Moes, E. W. 346, 352, 353, 414
‘ Moleculae vivae’ (Linnaeus) 377
Molhuysen, P. C. 326, 412
Molijn, Jacob 21, 22
Molijn, Jan 21
Molliére, H. 374, 414
Molyneux, T. 17, 56 sqq, 60, 62, 414
Molyneux, W. 56, 59 sq, 414
Monas 121, 122, 123, 124, 125, 126,
127, 142, 143, 271
Monpart 414
Moore, J. 186
Moray, R. 14; & vide Robertson
More, T. 14, 73, 414
Morre, G. 29, 30, 37, 101, 102, 305,
414
Morris, W. 7
Mortreux, E. 414
Mosquito-larvae 256
Mother, L.’s 16, 18, 20, 22
Motley, J. L. 12, 27, 414
Mountague, W. 25 sq, 414
Mouth, animalcules in the 236 sqq,
296
Miller, O. F. 285, 376 sq, 381, 414
Multiplication of animalcules 297 sq ;
& alibi
Municipal appointments, L.’s 31 sqq
Muré, J. B. A. 339
Muscae volitantes 90
Mussel-water, animalcules in 207 sqq
Muys, W. G. 337, 414
Naber, H. A. 21, 414
Nachet, A. 326, 327, 414
Nagler, K. 118, 119, 415
Name, L.’s 300 sqq
Narez, U. 82
Needham, T. 379, 380, 415
Neeltge van Leeuwenhoek, vide
Sisters, L.’s
New Church, Delft 21, 22, 25, 26,
28, 29, 35
Newton, I. 70, 237
INDEX
New York 33
Nicholas, E. 28
Nieuwenhuis, G. 54, 415
Noctiluca 381
| Nonionina 263
Noordenbos, T. U. 415
Nordenskiodld, E. 321, 415
Nosema 382
Nutmeg-water, animalcules in 159
Sqq
Nuttall, G. H. F. 48, 415
Nyander, J. C. 378, 415
Nyctotherus 233, 234, 235, 236
Objects before L.’s lenses 322 sqq
Obreen, F. D. O. 35, 36, 415
‘Observing person in the country’
(Anonymus, 1677) 373, 378, 399
Ockers, P. 34
Oecophora leeuwenhoekella 384
Old Church, Delft 22, 24, 26, 28,
29, 30,99 sq; & alibi
Oldenburg, H. 37, 38, 39, 40, 41,
AS (44 AG, AT, Si, 109) 111, Pha,
114) MS 116; 1172018, 119 et,
; 128, .129;.136, 139, 149, 167;
72, 7s, 182, 216,217, 238;
, 307, 331, 333, 342, 357, 358,
Oliver, F. W. 415
Oniscus 224
| Opalina 233, 234, 235, 236
Opuscula Selecta Neerlandicorum 415
Ornstein, M. 37, 53, 415
Osborne, D. 12, 45, 415
| Ostade, A. van 352
Oudemans, A. C. [acarologist] 384,
415
Oudemans, A. C.
312, S13, 413
Oxysoma 231
Oxytricha 149
Oxyuris 208, 231
Oyster-water, animalcules in 206,
207
(lexicographer]
Pagel 348 ; & vide Hirsch
Pandorina leuwenhoeku 384
Panicum, vide Millet-seed
Pansier, P. 364, 416
Paramecium 164, 210, 376
INDEX
Pars, A. 416
Pasteur, L. 199, 356, 374, 382, 416
Pediculus 336; & vide Louse
Pepper-water, animalcules in 131 sqq,
165, 166, 182, 183, 185, 187, 197,
200
Pepys, 5. 12, 25, 38, 129, 186, 416
Peter the Great 55
Petiver, J. 78
Petrie, A. 174, 175
Phacus 164
Philosophical Transactions 389; &
passim
Philips van Leeuwenhoek, vide
Father, L.'s
Phillips, L. B. 416
Pigeon, animalcules in a 228
Pijzel, E. D. 24, 309, 416
* Pissabed ’ 224
Plietzsch, E. 36, 416
Plintmer, Hi. G. 22, 23,33; 416
Pliny 95, 367, 384, 416
Poitevin, R. 176
Pollock, F. 113, 176, 416
Polystomella 263
Polytoma 297 sq
Pond-water, animalcules in 295 sqq
Poot, H. 101, 345, 416
Portraits of L. 346 sqq
Power, H. 141, 362, 364, 365, 416
Prescott, F. 252, 416
Pritze, F. 229, 236, 416
Pritzel, G. A. 388, 416
“ Protozoa ’ 378
Prowazek, S. von 236, 245, 416
Pseudospira 141; & vide Dobell
(1912)
Publications, L.’s 390 sqq
Pusey, E. B. 8
Rabus, P. 396, 416 ; letters to 396 sq
Radl, E. 385, 416
Rain-water, animalcules in 117 sqq,
205, 271
Raja 139
Rana esculenta 231, 233, 234, 235,
236; R. temporaria 231, 233, 234,
235
hays ee ee, Oly) SZ, 109; 112) 263;
264, 416
Record of the Royal Society 417
433
Redi, F. 196, 199, 364, 417
Réga, H. J. 82
Register van alle de Werken, vide
Anonymus (1695)
Regley, l Abbé 417
Rémignard, H. 373, 417
Rhede, Baron van 206, 262
Rhizopoda 262
Richardson, 8, W: 22: 31) 322.33:
53, 304, 417
Riemsdijk, B. W. F. van 346, 417
River-water, animalcules in 128
Rix, FL 38,417
Robertson, A. 417
Robin, C. 246, 417
Robinson, H. W. 237
Rosel von Rosenhof, A. J. 282, 378,
417
Rogers) aj oR. 1417
Rooijen, A. J. Servaas van 80, 82,
103, 390, 417
Roos, J. C. 378, 418
Rosenheim, O. 418
Rotalia 263
Rotermund, H. W. 418
Rotifers 110, 121, 263 sqq, 278 sqq,
291, 292, 293, 294, 297, 384
Roukema, R. 385, 418
Roy, J. le 177
Royal Society 37 ; & passim
Royal Society MSS. 356 sqq, 388 sqq ;
& passim
Ruijsch, F. 84
Ruisdael, J. van 129
Ruyter, M. de 39
Sabrazés, J. 326, 362, 418
Sachs, J. 382, 383, 418
Sale-Catalogue of L.’s microscopes
320 sq
Saliva, animalcules in 238 sqq
Salting, G. 351
Salvino d’Armato 364
Sandgrains 334 sq; & passim
Sarcina 246
Saussure, H. B. de 380, 418
Scheltema, P. 84, 418
Schevelinge = Scheveningen 129
Schierbeek, Ay. 120) 21) 2323)
27, 29, 30, 31, 34, 37, 99, 100, 281,
300, 302, 341, 418, 424
434
Schill, J. F. 109, 418
Schooling, L.’s 23
Schrank, F. von Paula 384
Schultsz, J. C. 340
Scriptores ret rusticae 418
Scriverius, P. 24, 418
Seals, L.’s 359 sqq
Sea-water, animalcules in 129 sqq
Sections, histological 333
Selenomonas 245, 246
Selle, M. 425
Senebier, J. 380, 418
Seters, W. Ho van 115,116, 333,
346, 355, 359, 387, 390, 418, 424
Sewel, W. 129, 263, 312, 313, 418
Sherborn, C. D. 384, 419
Shop, L.’s 29, 338 sqq
Shrimp’s stomach, shell in 262
Singer, C. 246, 247, 363, 365, 366,
367, 368, 370, 374, 419
Singer, D. 370, 419
Sinia, R. 117, 419
Sisters, L.’s 18, 21, 22
Slabber, M. 381, 419
Slare, F. 230, 373, 419
Sloane, H. 78, 79, 256, 389
Smith, A. 350
Snelleman, J. F. 115, 390, 419
Snijders, E. P. 149, 424
Soil, animalcules in 297
Sons, L.’s 18, 28
Soutendam, J. 19, 20, 31, 48, 102,
338, 339, 419
Spallanzani, L. 199, 260, 304, 379,
380, 419
Sparshall, J. 381
Spermatozoa 6, 104, 121, 184, 221,
228, 230, 296, 377, 378
Spermine, vide Rosenheim
Sphaerella, vide Haematococcus
Spina, A. de 364
Spinoza, B. de 19, 113, 176, 308, 419
Spirillum 143, 144, 179, 214, 245
‘ Spirillum’ sputigenum 245
* Spirochaeta buccalis’ 241, 246
Spirochaetes 225, 229, 241, 246,
250, Zan,
Spirogyra 110
Spirulina 110, 380
Spoors, Surveyor 35
Sporozoa 220
INDEX
Sprat, T. 12, 37, 419
Statius, 94, 96
Stein, F. von 229, 419
Stelluti, F. 364, 365, 419
Stepfather, L.’s, vide Molijn, Jacob
Stirling, W. 419
Storr-Best, Ll. 369, 419
Strick, Jeol, .32
Strong, R. P. 229, 420
Stuart, A. 78, 79
Sturm, J.-C. 372, 420
Stylonychia 126
Surveyor, L. qualifies as 34, 354
Swalmius, Cornelia 16, 18, 31, 52, 240
Swammerdam, J. 24, 39, 74, 111,
117, 118, 130, 420
Sydenham, T. 186
Sylvius 39
Tabanus 221
Tabellaria 372
Tanner, J. R. 420
Targioni-Tozzetti, G. 46, 179, 360,
390, 397, 420
Teeth, animalcules on the 238 sqq
Temple, W. 12, 40, 45, 129, 420
Testimonials 172, 173, 174 sqq
Thompson, D’Arcy W. iii, 94, 190,
423
Thomson, T. 12, 420
Thorpe, E. 420
Thread-bacteria 135, 141, 165
Tomb, L.’s 100, 101, 102
Tongue, animalcules from the 254
Totton, A..K 337
Town Hall, Delft 26
‘ Trees,’ metallic 291
Trembley, A. 281, 282, 380, 420
Trepomonas 210
Trevelyan, G. M. 420
Treviranus, G. R. 420
Trichodina 282, 285
Trichomastix |=Eutrichomastix} 231,
234, 236
Trichomonas 224, 229, 231, 234, 236,
246, 247
Tromp, M. 26
Trustee (for Vermeer) 35 sq
Tschirnhausen, E. W. von 338
Tyndale, W. 308
Tyndall, J. 199, 420
INDEX 435
Uffenbach, Z. C. von 56, 63 sqq, 77,
325, 420
Uncle, L.’s 18, 23, 300
“ Unpublished letters ’ (1-27) 356 sqq
Uttenbroek 360
Vallisneri, A. 303, 375, 420, 421 |
Vandevelde, A. J. J. 43, 109, 115, |
116, 117, 173, 256, 263, 270, 275, |
285, 333, 356, 359, 362, 390, 421 |
Vanellus 134
Van Heurck, H. 326
Vanzype, G. 36, 421
Varro 369, 418, 419 |
Veldman, H. S. 347, 421
Verkolje, J. 49, 72, 325, 340, 343,
345, 346 sqq, 350, 351, 353, 354,
361
Vermeer, J. 19, 25, 28, 35, 36, 125,
345, 353 sq
‘Vessels ’ in animalcules 189 sqq
Vinegar, animalcules in 150 sqq
Vinegar-eel 141, 150 sqq, 179, 225, |
243, 325
Vine-sap, animalcules in 193sqq_ |
Virgil 80
Virlin, Maria 28
Volvox 256 sqq, 377, 380, 384
Vorticella & Vorticellidae 118 sq,
133, 136, 148, 156 sg, 164, 208, |
2/7 sag, 283, 285, 291, 292, 293,
294, 295, 377, 381
Vries, J. de 103
Waard, C. de 363, 421
Waller, R. 47, 348, 421
Ward, N. 12, 421
Water-flea 111, 118, 130, 273
Weights, L.’s 337 sq
Weld, C; R. 12, 37,39, 96,99, 237,
421
Well-water, animalcules in 128
Wendel, A. J. 347
Wenyon, C. M. 246, 247, 421
Werff, J. van der 80
Wheatley, H. B. 304, 416
Whewell, W. 422
White, A. H. 326, 423
| Wild Boar, College of the 82
| Wildeman, M. G. 29, 101, 422
Wilkins, J. 38, 422
Will, L.’s 103
William I (the Silent) 25, 26
William III 25, 26, 104, 317
Williams-Ellis, A. 52, 347, 422
Williamson, J. 49
Willnau, C. 379, 422
Wilt, T. van der 93, 343 sqq
Wilt, W. van der 344 sq
Wine-gauger, L. appointed 37
| Wives, L.’s; wide Mey, B. de, ©
Swalmius, C.
| Wolf, A. 422
Woodruff, L. L. 376, 422
| Worp, J. A. 43, 422
Wren, C. 19, 186, 231
Wrisberg, H. A. 303, 379, 422
Writings, L.’s 44sqg, 388 sqq
Zacharias Janssen 363
Zahn, J. 422
Zoelen, H. van 359
Zoogloea 160
Zwalmius, vide Swalmius
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