4. The manner in which our lenses reveal its structure, not merely amplify
its form.
[Footnote 5: The pygidium of the flea, very highly magnified, was here
shown.]
[Footnote 6: An illustration of the pygidium structure seen with
one-thirty-fifth immersion was given.]
Now with these simple and yet needful preliminaries you will be able to
follow me in a careful study of the least, the very lowliest and smallest,
of all living things. It lies on the very verge of our present powers of
optical aid, and what we know concerning it will convince you that we are
prepared with competent skill to attack the problem of the life-histories
of the smallest living forms. The group to which the subject of our
present study belongs is the bacteria. They are primarily staff-like
organisms of extreme minuteness, but may be straight, or bent, or curved,
or spiral, or twisted rods. This entire projection is drawn on glass, with
_camera lucida_, each object being magnified 2,000 diameters, that is to
say, 4,000,000 of times in area. Yet the entire drawing is made upon an
area of not quite 3 inches in diameter, and afterward projected here. The
objects therefore are all equally magnified, and their relative sizes may
be seen. The giant of the series is known as _Spirillum volutans;_ and you
will see that the representative species given become less and less in
size until we reach the smallest of all the definite forms, and known to
science as _Bacterium termo_.
Now within given limits this organism varies in size, but if a fair
average be taken its size is such that 50,000,000 laid in order would only
fill the hundredth of a cubic inch. Now the majority of these forms _move_
with rapidity and grace in the fluids they inhabit. But how? By what
means? By looking at the largest form of this group, you will see that it
is provided with two delicate fibers, one at each end. Ehrenberg and
others strongly suspected their existence, and we were enabled, with more
perfect lenses, to _demonstrate_ their presence some twelve years ago.
They are actually the swimming organs of this Spirillum. The fluid is
lashed rhythmically by these fibers, and a spiral movement of the utmost
grace results. Then do the intermediate forms that move also possess these
flagella, and does this least form in nature, viz., _Bacterium termo_,
accomplish its bounding and rebounding movements in the same way? Yes! by
a series of resolute efforts, in using a new battery of lenses--the finest
that at that time had ever been put into the hands of man--I was enabled
to show in succession that each motile form of Bacterium up to _B.
lineola_ accomplished its movements by fibers or flagella; and that in the
act of self-division, constantly taking place, a new fiber was drawn out
for each half before separation.
But the point of difficulty was _B. termo_. The demonstration of its
flagella was a task of difficulty which only patient purpose could
conquer. But by the use of our new lenses, and special illumination we--my
colleague and I--were enabled to demonstrate clearly a flagellum at each
end of this least of living organisms, as you see, and by the rapid
lashing of the fluid, alternately or together, with these flagella, the
powerful, rapid, and graceful movements of this smallest known living
thing are accomplished. Of course these fibers are inconceivably
fine--indeed for this very reason it was desirable, if possible, to
_measure_ it, to discover its actual thickness. We all know that, both for
the telescope and the microscope, beautiful apparatus are made for
measuring minute magnified details. But unfortunately no instrument
manufactured was delicate enough to measure _directly_ this fiber. If it
were measured it must be by an indirect progress, which I accomplished
thus: The diameter of the body of _B. termo_, _i.e._, from; side to side,
may in different forms vary from the 1/20000 to the 1/50000 of an inch.
_That_ is a measurement which we may easily make directly with a
micrometer. Haying ascertained this, I determined to discover the ratio of
thickness between the body of the Bacterium and its flagellum--that is to
say, to discover how many of the flagella laid side by side would make up
the width of the body.
I proceeded thus: This is a complicated microscope placed on a tripod, so
arranged that it may be conveniently worked upright. There is a special
instrument for centering and illuminating. On the stage of the instrument,
the Bacterium with its flagellum in distinct focus is placed. Instead of
the simple eyepiece, _camera lucida_ is placed upon it. This instrument is
so constructed that it appears to throw the image of the object upon the
white sheet of paper on the small table at the right hand where the
drawing is made, at the, same time that it enables the same eye to see
the pencil and the right hand. In this way I made a careful drawing of _B.
termo_ and its flagellum, magnified 5,000 diameters. Here is a projection
of the drawing made. But I subsequently avoided paper, and used under the
camera most carefully prepared surface of ground glass. When the drawing
was made I placed on the drawing a drop of Canada balsam, and covered it
with a circle of thin glass, just like any other microscopic mounted
object. This is a micro-slide so prepared. Now you can see that I only
have to lay this on the stage of a microscope, make it an object for a low
power, and use a screw micrometer to find how many flagella go to the
making of a body. The result is given in the figure; you see that ten
flagella would fill the area occupied by the diameter of the body.
In the case chosen the body was the 1/20,400 of an inch wide, and
therefore, when divided by ten, gave for the flagellum a thickness of the
1/204,000 of an English inch. In the end I made fifty separate drawings
with four separate lenses. I averaged the result in each fifty, and then
took the average of the total of 200, and the mean value of the width of
the flagellum was the 1/204,700 of an English inch. It will be seen, then,
that we are possessed of instruments which, when competently used, will
enable us to study the life-histories of the putrefactive organisms,
although they are the minutest forms of life. I have stated that they were
the inevitable accompaniments of putrescence and decay. You learned from a
previous illustration the general appearance of the Bacteria; they are the
earliest to appear whenever putrefaction shows itself. In fact the pioneer
is this--the ubiquitous _Bacterium termo._ The order of succession of the
other forms is by no means certain. But whenever a high stage of
decomposition is reached, a group of forms represented by these three will
swarm the fluid. These are the Monads, they are strictly putrefactive
organisms, they are midway in size between the least and largest Bacteria,
and are, from their form and other conditions, more amenable to research,
and twelve years ago I resolved, with the highest power lenses and
considerable practice in their use, to attack the problem of their origin;
whether as physical products of the not-living, or as the natural progeny
of parents.
But you will remember that only a minute drop of fluid containing them can
be examined at one time. This minute drop has to be covered with a minute
film of glass not more than the 1/200 of an inch thick. The highest lenses
are employed, working so near as almost to touch the delicate cover.
Clearly, then, the film of fluid would rapidly evaporate and cause the
destruction of the object studied. To prevent this an arrangement was
devised by which the lens and the covered fluid under examination were
used in an air-tight chamber, the air of which was kept in a saturated
condition; so that being, like a saturated sponge, unable to take in any
more, it left the film of fluid unaffected. But to make the work efficient
I soon found that there must be a second observer. Observation by leaps
was of no avail. To be accurate it must be unbroken. There must be no gap
in a chain of demonstration. A thousand mishaps would occur in trying to
follow a single organism through all the changes of successive hours to
the end. But, however many failures, it was evident, we must begin on
another form at the earliest point again, and follow it to the close. I
saw soon that every other method would have been merely empirical, a mere
piecemeal of imagination and fact. When one observer's ability to continue
a long observation was exhausted, there must be another at hand to take up
the thread and continue it; and thus to the end. I was fortunate indeed at
this time in securing the ready and enthusiastic aid of Dr. J.J. Drysdale,
of Liverpool, who practically lived with me for the purpose, and went side
by side with me to the work. We admitted nothing which we had not both
seen, and we succeeded each other consecutively, whenever needful, in
following to the end the complete life-histories of six of these
remarkable forms.
I will now give you the facts in relation to two which shall be typical.
We obtained them in enormous abundance in a maceration of fish. I will not
take them in the order of our researches, but shall find it best to
examine the largest and the smallest. The appearance of the former is now
before you. It is divergent from the common type when seen in its perfect
condition, avoiding the oval form, but it resumes it in metamorphosis. It
is comparatively huge in its proportions, its average extreme length being
the 1/1000 of an inch. Its normal form is rigidly adhered to as that of a
rotifer or a crustacean. Its body-substance is a structureless sarcode.
Its differentiations are a nucleus-like body, not common to the monads;
generally a pair of dilating vacuoles, which open and close, like the
human eyelid, ten to twenty times in every minute; and lastly, the usual
number of four flagella. That the power of motion in these forms and in
the Bacteria is dependent upon these flagella I believe there can be no
reasonable doubt. In the monads, the versatility, rapidity, and power of
movement are always correlated with the number of these. The one before us
could sweep across the field with majestic slowness, or dart with
lightning swiftness and a swallow's grace. It could gyrate in a spiral, or
spin on its axis in a rectilinear path like a rifled bullet. It could dart
up or down, and begin, arrest, or change its motion with a grace and power
which at once astonish and entrance. Fixing on one of these monads then,
we followed it doggedly by a never-ceasing movement of a "mechanical
stage," never for an instant losing it through all its wanderings and
gyrations; We found that in the course of minutes, or of hours, the
sharpness of its outline slowly vanish, its vacuoles disappeared, and it
lost its sharp caudal extremity, and was sluggishly amoeboid. This
condition tensified, the amoeboid action quickened as here depicted, the
agility of motion ceased, the nucleus body became strongly developed, and
the whole sarcode was in a state of vivid and glittering action.
If now it be sharply and specially looked for, it will be seen that the
root of the flagella _splits_, dividing henceforth into two separate
pairs. At the same moment a motion is set up which pulls the divided pairs
asunder, making the interval of sarcode to grow constantly greater between
them. During this time the nuclear body has commenced and continued a
process of self-division; from this moment the organism grows rapidly
rounder, the flagella swiftly diverge. A bean-like form is taken; the
nucleus divides, and a constriction is suddenly developed; this deepens;
the opposite position of the flagella ensues, the nearly divided forms
now vigorously pull in opposite directions, the constriction is thus
deepened and the tail formed. The fiber of sarcode, to which the
constricted part has by tension been reduced, now snaps, and two organisms
go free. It will have struck you that the new organism enters upon its
career with only _two_ flagella, and the normal organism is possessed of
four. But in a few minutes, three or four at most, the full complement
were always there. How they were acquired it was the work of months to
discover, but at last the mystery was solved. The newly-fissioned form
darted irregularly and rapidly for a brief space, then fixed itself to the
floor or to a rigid object by the ends of its flagella, and, with its body
motionless, an intense vibratory action was set up along the entire length
of these exquisite fibers. Rapidly the ends split, one-half being in each
fiber set free, and the other remaining fixed, and in 130 seconds each
entire flagellum was divided into a perfect pair.
Now the amoeboid state is a notable phenomenon throughout the monads as
precursive of striking change. It appears to subserve the purpose of the
more facile acquisition and digestion of food at a crisis. And this
augmented the difficulty of discovering further change; and only
persistent effort enabled us to discover that with comparative rareness
there appeared a form in an amoeboid state that was unique. It was a
condition chiefly confined to the caudal end, the sarcode having became
diffluent, hyaline, and intensely rapid in the protrusion and retraction
of its substance, while the nuclear body becomes enormously enlarged.
These never appear alone; forms in a like condition are diffused
throughout the fluid, and may swim in this state for hours. Meanwhile, the
diffluence causes a spreading and flattening of the sarcode and swimming
gives place to creeping, while the flagella violently lash. In this
condition two forms meet by apparent accident, the protrusions touch, and
instant fusion supervenes. In the course of a few seconds there is no
disconnected sarcode visible, and in five to seven minutes the organism is
a union of two of the organisms, the swimming being again resumed, the
flagella acting in apparent concert. This may continue for a short time,
when movement begins to flag and then ceases. Meanwhile, the bodies close
together, and the eyenots or vacuoles melt together, the two nuclei become
one and disappear, and in eighteen hours the entire body of "either has
melted into other," and a motionless, and for a time irregular, sac is
left. This now becomes smooth, spherical, and tight, being fixed and
motionless. This is a typical process; but the mingled weariness and
pleasure realized in following such a form without a break through all the
varied changes into this condition is not easily expressed.
But now the utmost power of lenses, the most delicate adjustment of light,
and the keenest powers of eyesight and attention must do the rest. Before
the end of six hours the delicate glossy sac opens gently at one place,
then there streams out a glairy fluid densely packed with semi-opaque
granules, just fairly visible when their area was increased six millions
of times, and this continued until the whole sac was empty and its entire
contents diffused. To follow with our utmost powers these exquisite specks
was an unspeakable pleasure, a group seen to roll from the sac, when
nearly empty, were fixed and never left. They soon palpably changed by
apparent swelling or growth, but were perfectly inactive; but at the end
of three hours a beaked appearance was presented. Rapid growth set in, and
at the end of another hour, how has entirely baffled us, they acquired
flagella and swam freely; in thirty-five minutes more they possessed a
nucleus and rapidly developed, until at the end of nine hours after
emission a sporule was followed to the parent condition and left in the
act of fission. In this way, with what difficulties I need not weary you,
a complete life-cycle was made out.
And now I will invite your attention to the developmental history of the
_most minute_ of the six forms we studied. In form it is a long oval, it
is without visible structure or differentiation within, and is possessed
of only a single flagellum. Its utmost length is the 1/5000 of an inch.
Its motion is continuous in a straight line, and not intensely rapid, nor
greatly varied, being wholly wanting in curves and dartings. The
copiousness of its increase was, even to our accustomed eyes, remarkable
in the extreme, but the reason was discovered with comparative ease. Its
fission was not a division into two, but into many. The first indication
of its approach in following this delicate form was the assumption rapidly
of a rounder shape. Then followed an amoeboid and uncertain form, with
an increased intensity of action which lasted a few moments, when
lassitude supervened, then perfect stillness of the body, which is now
globular in form, while the flagellum feebly lashed, and then fell upon
and fused with the substance of the sarcode. And the result is a solid,
flattened, homogeneous ball of living jelly.
To properly study this in its further changes, a power of from three to
four thousand diameters must be used, and with this I know of few things
in the whole range of minute beauty more beautiful than the effect of what
is seen. In the perfectly motionless flattened sphere, without the shimmer
of premonition and with inconceivable suddenness, a white cross smites
itself, as it were, through the sarcode. Then another with equal
suddenness at right angles, and while with admiration and amazement one
for the first time is realizing the shining radii, an invisible energy
seizes the tiny speck, and fixing its center, twists its entire
circumference, and endows it with a turbined aspect. From that moment
intense interior activity became manifest. Now the sarcode was, as it
were, kneading its own substance, and again an inner whirling motion was
visible, reminding one of the rush of water round the interior of a hollow
sphere on its way to a jet or fountain. Deep fissures or indentations
showed themselves all over the sphere; and then at the end of ten or more
minutes all interior action ceased, and the sphere had segmented into a
coiled mass. There was no trace of an investing membrane; the constituent
parts were related to each other simply as the two separating parts of an
ordinary fission; and they now commenced a quick, writhing motion like a
knot of eels, and then, in the course of from seven to thirty minutes,
separated, and fully endowed with flagella swam freely away, minute but
perfect forms, which by the rapid absorption of pabulum attained speedily
to the parent size.
It is characteristic of this group of organic forms that multiplication
by self-division is the common and continuous method of increase. The
other and essential method was comparatively rare and always obscure. In
this instance, on the first occasion the continuous observation of the
same "field" for five days failed to disclose to us any other method of
increase but this multiple-fission, and it was only the intense
suggestiveness of past experience that kept us still alert and prevented
us from inferring that it was the _only_ method. But eventually we
perceived that while this was the prevailing phenomenon, there were
scattered among the other forms of the same monad _larger_ than the rest,
and with a singular granular aspect toward the flagellate end. It may be
easily contrasted with the normal or ordinary form. Now by doggedly
following one of these through all its wanderings a wholly new phase in
the morphology of the creature was revealed. This roughened or granular
form seized upon and fastened itself to a form in the ordinary condition.
The two swam freely together, both flagella being in action, but it was
shortly palpable that the larger one was absorbing the lesser. The
flagellum of the smaller one at length moved slower, then sluggishly, then
fell upon the sarcode, which rapidly diminished, while the bigger form
expanded and became vividly active until the two bodies had actually fused
into one. After this its activity diminished, in a few minutes the body
became quite still, leaving only a feeble motion in the flagellum, which
soon fell upon the body-substance and was lost. All that was left now was
a still spheroidal glossy speck, tinted with a brownish yellow. A
peculiarity of this monad is the extreme uncertainty of the length of time
which may elapse before even the most delicate change in this sac is
visible. Its absolute stillness may continue for ten or more hours. During
this time it is absolutely inert, but at last the sac--for such it
is--opens gently, and there is poured out a brownish glairy fluid. At
first the stream is small, but at length its flow enlarges the rift in the
cyst, and the cloudy volume of its contents rolls out, and the hyaline
film that inclosed it is all that is left.
The nature of the outflow was like that produced by the pouring of strong
spirit into water. But no power that we could employ was capable of
detecting a _granule_ in it. To our most delicate manipulation of light,
our finest optical appliances, and our most riveted attention, it was a
homogeneous fluid and nothing more. This for a while baffled and disturbed
us. It lured us off the scent. We inferred that it might possibly be a
fertilizing fluid, and that we must look in other directions for the
issue. But this was fruitless, and we were driven again to the old point,
and having once more obtained the emitted fluid, determined to fix a lens
magnifying 5,000 diameters upon a clear space over which the fluid had
rolled, and near to the exhausted sac, and ply our old trade of _watching_
with unbroken observation.
The result was a reward indeed. At first the space was clear and white,
but in the course of a hundred minutes there came suddenly into view the
minutest conceivable specks. I can only compare the coming of these to the
growth of the stars in a starless space upon the eye of an intense watcher
in a summer twilight. You knew but a few minutes since a star was not
visible there, and now there is no mistaking its pale beauty. It was so
with these inexpressibly minute sporules; they were not there a short time
since, but they grew large enough for our optical aids to reveal them, and
there they were. Such a field after one hour's watching I present to you.
And here I would remark that these delicate specks were unlike any which
we saw emerge directly from the sac as granules. In that condition they
were always semi-opaque, but here they were transparent, and a brown
yellow, the condition always sequent upon a certain measure of growth.
To follow these without the loss of an instant's vision was pleasure of
the highest kind. In an hour and ten minutes from their first discovery
they had grown to oval points. In one hour more the specks had become
beaked and long. And this pointed end was universally the end from which
the flagellum emerged. With the flagellum comes motion, and with that
abundant pabulum, and therefore rapid growth. But when motion is attained
we are compelled to abandon the mass and follow one in all its impetuous
travels in its little world; and by doing so we are enabled to follow the
developed speck into the parent condition and size, and not to leave it
until it had, like its predecessors, entered on and completed its
wonderful self-division by fission.
It becomes then clearly manifest that these organisms, lowly and little as
they are, arise in fertilized parental products. There is no more caprice
in their mode of origin than in that of a crustacean or a bird. Their
minuteness, enormous abundance, and universal distribution is the
explanation of their rapid and practically ubiquitous appearance in a
germinating and adult condition. The presence of putrefiable or putrescent
matter determines at once the germination of the always-present spore. But
a new question arises. These spores are definite products. In the face of
some experimental facts one was tempted to inquire: Have these spores any
capacity to resist heat greater than the adults? It was not easy to
determine this question. But we at length were enabled to isolate the
germs of seven separate forms, and by means of delicate apparatus, and
some twelve months of research, to place each spore sac in an apparatus so
constructed that it could be raised to successive temperatures, and
without any change of conditions examined on the stage of the microscope.
In this way we reached successive temperatures higher and higher until the
death point--the point beyond which no subsequent germination ever
occurred--was reached in regard to _each_ organism. The result was
striking. The normal death point for the adult was 140° F. One of the
monads emitted from its sac minute mobile specks--evidently living
bodies--which rapidly grew. These we always destroyed at a temperature of
180° F. Three of the sacs emitted spores that germinated at every
temperature under 250° F. Two more only had their power of germination
destroyed at 260° F. And one, the least of all the monad forms, in a heat
partially fluid and partially dry, at all points up to 300° F. But if
wholly in fluid it was destroyed at the point of 290° F. The average being
that the power of heat resistance in the spore was to that of the adult
as 11 to 6. From this it is clear that we dare not infer spontaneous
generation after heat until we know the life-history of the organism.
In proof of this I close with a practical case. A trenchant and resolute
advocate of the origin of living forms _de novo_ has published what he
considers a crucial illustration in support of his case. He took a strong
infusion of common cress, placed it in a flask, boiled it, and, while
boiling, hermetically sealed it. He then heated it up in a digester to
270° F. It was kept for nine weeks and then opened, and, in his own
language, on microscopical examination of the earliest drop "there
appeared more than a dozen very active monads." He has fortunately
measured and roughly drawn these. A facsimile of his drawing is here. He
says that they were possessed of a rapidly moving lash, and that there
were other forms without tails, which he assumed were developmental stages
of the form. This is nothing less than the monad whose life-history I gave
you last. My drawings, magnified 2,500 diams., of the active organism and
the developing sac are here.
Now this experimenter says that he took these monads and heated them to a
temperature of about 140° F., and they were all absolutely killed. This is
accurately our experience. But he says these monads arose in a closed
flask, the fluid of which had been heated up to 270° F. Therefore, since
they are killed at 140° F., and arose in a fluid after being heated to
270° F., they must have arisen _de novo!_ But the truth is that this is
the monad whose spore only loses its power to germinate at a temperature
(in fluid) of 290°, that is to say, 20° F. higher than the heat to which,
in this experiment, they had been subjected. And therefore the facts
compel the deduction that these monads in the cress arose, not by a change
of dead matter into living, but that they germinated naturally from the
parental spore which the heat employed had been incompetent to injure.
Then we conclude with a definite issue, viz., by experiment it is
established that living forms do not now arise in dead matter. And by
study of the forms themselves it is proved that, like all the more complex
forms above them, they arise in parental products. The law is as ever,
only that which is living can give origin to that which lives.
* * * * *
A catalogue, containing brief notices of many important scientific papers
heretofore published in the SUPPLEMENT, may be had gratis at this office.
* * * * *