Philip Henry Gosse.

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to turn aside the force of this circumstance by asserting
that he had cut some raw beef with the knife, and had
omitted to wipe it.

The knife was submitted to an eminent professor of
microscopy, who immediately discovered the following
facts: 1. The stain was certainly blood. 2. It was not
the blood of a piece of dead flesh, but that of a living
body; for it had coagulated where it was found. 3. It was
not the blood of an ox, sheep, or hog. 4. It was human
blood. Besides these facts, however, other important
ones were revealed by the same mode of investigation.

5. Among the blood were found some vegetable fibres.

6. These were proved to be cotton fibres agreeing with those



BLOOD 39

of the murdered man's shirt and neckerchief. 7. There .
were present also numerous tessellated epithelial cells. In
order to understand the meaning and the bearing of this
last fact, I must explain that the whole of the internal sur-
face of the body is lined with a delicate membrane (a con-
tinuation of the external skin), which discharges mucus,
and is hence termed mucous membrane. Now this is com-
posed of loose cells, which very easily separate, called
epithelial cells; they are in fact constantly in process of
being detached (in which state they constitute the mucus),
and of being replaced from the tissues beneath. Now
microscopial anatomists have learned that these epithelial
scales or cells, which are so minute as to be undiscernible
by the unaided eye, differ in appearance and arrangement
in different parts of the body. Thus, those which line the
gullet and the lower part of the throat are tessellated, or re-
semble the stones of a pavement; those that cover the root
of the tongue are arranged in cylinders or tall cones, and are
known as columnar; while those that line some of the vis-
cera of the abdomen carry little waving hairs (cilia) at
their tips, and are known as ciliated epithelium.

The result of the investigation left no doubt remaining
that with that knife the throat of a living human being,
which throat had been protected by some cotton fabric,
had been cut. The accumulation of evidence was fatal to
the prisoner, who without the microscopic testimony might
have escaped.

But what was there in the dried brown stain that de-
termined it to be blood? And, particularly, how was
it proved not to be the blood of an ox, as the prisoner
averred ? To these points we will now give a moment's
attention.



40 EVENINGS AT THE MICROSCOPE

With tliis fine needle I make a minute prick through,
the skin of my hand. A drop of blood oozes out, with
which I smear this slip of glass. The slip is now on the
stage of the instrument, with a power of 600 diameters.
You see an infinite number of small roundish bodies, of a
clear yellowish color, floating in a colorless fluid, but so
numerous that it is only here and there, as near the edges
of the smear, that you can detect any interval in their
continuity.

These bodies are what we frequently call the blood-
globules, or, more correctly, blood- disks; since their form
is not globular, but thin and flat, like a piece of money.
The slightness of their color is dependent on their extreme
tenuity: when a large number lie over each other the ag-
gregated color is very manifest, as it then becomes either
a full dark red, or bright rich scarlet; for to these disks
blood is entirely indebted for its well-known hue. All
vertebrate blood is composed principally of these bodies,
which, when once seen, are easily recognized again: the
microscope then readily determines whether any given red
fluid or dried stain is composed of blood.

The disks in the blood of Mammalia are circular, or
nearly so, and slightly concave on both of the surfaces.
On the other hand, in Birds, Fishes, and Eeptiles their
form is elliptical, and the surfaces are flat, or slightly con-
vex. This distinction, then, will at once enable us to de-
termine Mammalian blood. 1 But to determine the various
tribes of this great class among themselves, we must have
recourse to another criterion that of dimensions.

1 The Camels among Mammalia, and the Lampreys among Fishes, are excep-
tions to the above rule; the former having elliptical and convex blood-disks,
and the latter circular, and slightly concave.



BLOOD 41

The blood-disks of Man nearly agree in size with those-
of the Monkey tribe, of the Seals and Whales, of the Ele-
phant, and of the Kangaroo. Most other quadrupeds have
them smaller than in Man ; the smallest of all being found
in the ruminating animals. The little Musk-deer of Java
has disks not more than one-fourth as large as the human,
but these are remarkably minute; no other known animal
approaches it in this respect: those of the Ox are about
three-fourths, and those of the Sheep little more than half
the human average.

Tables have been made out showing the comparative
size of these corpuscles in various animals, and such tables
are very useful; but we must bear in mind that the aver-
age dimensions only are to be looked for; since in any
given quantity of blood, under examination, we shall not
fail to see that some disks exceed, while others come short
of, the dimensions of the majority.

Generally speaking, the blood-disks in Birds and in
Fishes are about equal in size: their form is, however,
that of a more elongated ellipse in Birds than in Fishes.
They may be set down as averaging in breadth the diam-
eter of the human disks, while their length is about half
as much again, or a little more, in most Birds.

It is in Eeptiles that we meet with the largest disks,
and especially in those naked-skinned species, the Frogs
and Newts. A large species inhabiting the American lakes
Siren lacertina has disks of the extraordinary size of
l-400th of an inch long by 1 -800th broad, or about eight
times as large as those of Man. Our common Newts afford
us the largest examples among British animals, but they
do not reach above half the size just mentioned.

Taking this drop of blood from my finger as a standard



42 EVENINGS AT THE MICROSCOPE

of comparison, we find, on applying the micrometer, that
the disks run from l-2500th to l-5000th of an inch; but
that the great majority are about 1 -3300th in diameter. On
these slides are samples of other kinds. This is the blood
of a Fish the common Blenny or Shanny (Blennius pholis).
Here we see at once the oval form of the disks ; their aver-
age is l-2800th by l-SSOOth of an inch. Here is the blood
of a Frog (Rana temporaries)] these are more than twice
the size of the fish's; for they average l-1250th by 14800th




BLOOD-DISKS.

a, Man. 6, Blenny. c, Frog. d, Newt.

of an inch. And, finally, I can show you a drop of blood
from this Smooth-newt (Lissotriton punctatus). The large
size of the disks is now conspicuous, and so indeed is the
elegance of their form: in this case, as in the last, we see
in each disk a distinct roundish nucleus. These run from
1 -700th to l-950th in length, by 1-llOOth to l-1600th in
breadth; but the average are about 1 -800th. by l-1300th
of an inch.

It may interest you to see these blood-disks in their
proper situation, and to observe the motion which they
possess during the life of their owners. It is, indeed, one
of the most instructive modes of using this wonder-work-



BLOOD 43

ing instrument to look through it at living structures, and
watch the different processes of life as they are carried on
under our eyes. Nor is this at all difficult to accomplish;
for a large number of animals are so small that we can
easily put them upon the stage of the microscope, and
withal so transparent that their integuments and various
tissues offer little or no impediment to our discerning the
forms and movements of the contained viscera. And in
cases where the entire animal is too large to be viewed
microscopically as a whole, it sometimes happens that, by
a little contrivance, we can so secure the creature as to
look, without interruption, on certain parts of the body
which afford the requisite minuteness and transparency.

I have here a living Frog. You perceive that the web
which connects the toes is exceedingly thin and translucent,
yet arteries and veins meander through its delicate tissues,
which are then clothed on both surfaces with the common
skin. But you ask how we can induce the Frog to be so
polite as to hold his paw up and keep it steady for our
scientific investigation. We will manage that without
difficulty.

Most microscopes are furnished (among their accessory
apparatus) with what is called a frog-plate, provided for
this very demonstration. Here is mine. It is a thin plate
of brass, two inches and a half broad and seven long, with
a number of small holes pierced through it along the mar-
gins, and a large orifice near one end, which is covered
with a plate of glass. This is to be Froggy's bed during
the operation, for we must make him as comfortable as
circumstances will admit.

Well, then, we take this strip of linen, damp it, and
proceed to wrap up our unconscious subject. When we



44 EVENINGS AT THE MICROSCOPE

have passed two or three folds round him, we pass a tape
round the whole, with just sufficient tightness to keep him
from struggling. One hind- leg must project from the linen,
and we now pass a needle of thread twice or thrice through
the drapery and round the small of this free leg, so as to
prevent him from retracting it.

Here then he lies, swathed like a mummy, with one
little cold foot protruded. Lay him carefully on the brass
plate, so that the webbed toes shall stretch across the glass.
Now, then, we pass another tape through the marginal
holes, and over the body, to bind it to the brass ; of course
taking care not to cut the animal, but only using just as
much force as is needful to prevent his wrigglings. Now
a bit of thread round each toe, with which we tie it to as
many of the holes, so as to expand the web across the
glass. A drop of cold water now upon the swathes to
keep him cool, and a touch of the same with a feather
upon the toes to prevent them from drying (which must
be repeated at intervals during the examination) and he
is ready.

What a striking spectacle is now presented to us, as
with a power of 300 diameters we gaze on the web of the
foot! There is an area of clear colorless tissue filling the
field, marked all over with delicate angular lines, some-
thing like scales; this is the tessellated epithelium of the
surface. Our attention is caught by a number of black
spots, often taking fantastic forms, but generally somewhat
star-like: these are pigment cells, on which the color of
the animal's skin is dependent. But the most prominent
feature is the blood. Wide rivers, with tortuous course,
roll across the area, with many smaller streams meander-
ing among them; some pursuing an independent course



BLOOD 45

below the larger, and others branching out of them, or
joining them at different angles. The larger rivers are of
a deep orange-red hue, the smaller faintly tinged with red-
dish yellow. In some of these channels the stream rolls
with a majestic evenness; in others it shoots along with
headlong impetuosity; and in some it is almost, or even
quite, stagnant. By looking with a steady gaze, we see
that in all cases the stream is made up of a multitude of
thin reddish disks, of exactly the same dimensions and
appearance as those we* saw
just now in the Frog's blood;
only that here, being in mo-
tion, we see very distinctly,
as they are rolled over each
other, that they are disks,
and not spherules; for they
forcibly remind us of coun-
ters, such as are used for
play, supposing they were
made out of pale red glass.
It is charming to watch

One of these Streams, Select- CIRCULATION^N FROG'S FOOT!

ing one of medium size, where the density is not too great
to see the individual disks, and fixing our eye on the point
where a branch issues from one side of the channel, mark
the disks shoot by one after another, some pursuing their
main course, and others turning aside into the branch,
perhaps so small as to allow of only a single disk to pass
at once.

The streams do not pursue the same uniform direction.
The larger ones do indeed; and their course is from the
extremity of the toes toward the body i these are the




46 EVENINGS AT THE MICROSCOPE

veins; but the smaller streamlets flow in any direction,
and frequently send out side- branches, which presently
return into the stream from which they issued, or unite
with others in a very irregular network. These are the
capillaries, which feed the veins, and which are them-
selves fed by the arteries, whose course is in the opposite
direction; viz., from the body. These, however, are with
difficulty seen: they are more deeply seated in the tissues,
and are less spread over the webs, being generally placed
along the borders of the toes; they are, moreover, fewer
and smaller than the veins ; but the blood in them usually
flows with more impetuous rapidity.

The variations in the impetus of the current which we
observe in the same vessel are probably owing to the men-
tal emotions of the animal; alarm at its unusual position,
and at the confinement which it feels when it endeavors
to move, may suspend the action of the heart, and thus
cause an interruption in the flow; or analogous emotions
may quicken the pulse. We will, however, now release
our little prisoner, who, though glad to be at liberty, is,
as you see, none the worse for his temporary imprison-
ment.

Let us now look at the circulation of the blood in one
of the Invertebrate Animals. In this thin glass cell of
sea- water is a small fragment of sea- weed, and attached to
one of its slender filaments you may see three or four tiny
knobs of jelly, clustered together like a bunch of grapes.
These are animals; each endowed with a distinct life, but
associated together by a common stalk, which maintains
the mutual vital connection of the whole. It is one of the
Social Tunicata, and is named Perophora Listeri.

Though each globose knob is no larger than a small



BLOOD



pin's head, it is full of organs which carry on the various
functions of life; and, because the whole tissues are as
transparent as crystal, they allow us to watch the proc-
esses with perfect ease. Take a peep at it.

It is a gelatinous sac, of a form intermediate between
globular and cubical, flat-
tened on two opposite sides,
with a sort of wart at the
summit and another at the
side, each of which is!
pierced with a pursed ori-
fice. The upper of these
orifices admits water for
respiration and food; the
latter passes through a di-
gestive system, and is dis-
charged through the side
orifice. The digestive or-
gans lie on that flattened side, which is furthest from your
eye, and are therefore dimly seen.

The globose body is enclosed in a coating of loose
shapeless jelly that passes off from one of the lower cor-
ners, and forms a short foot-stalk, which unites with simi-
lar foot-stalks from the sister-globules, and all together are
attached to the sea-weed. Each foot-stalk has an organic
pore, into which a vessel passes upon the body.

Your attention is first arrested by the breathing sac,
with its rows of oblong cells all in wheel-like motion. It
is indeed a wonderful object; but for the present neglect
this, as we will return to it presently, and direct your
consideration to the course of the blood.

It is" true the fluid which I so name is not red, like




48 EVENINGS AT THE MICROSCOPE

that of the Frog which you have just been gazing at, nor
does it carry disks of the same elegantly regular form.
But you have the advantage here of tracing, at one view,
the whole course of the circulation, from its first rush out
of the heart to its return into that organ again.

At the bottom of the interior, below the breathing sac,
there is an oblong cavity, through whose centre there runs
a long transparent vessel, formed of a delicate membrane,
the appearance of which resembles that of a long bag,
pointed (but not closed) at either end, and then twisted
in some unintelligible manner so as to make three turns.
This is the heart; and within it are seen many minute
colorless globules, floating freely in a subtile fluid: this is
the nutrient juice of the body, which we may, without
much violence, designate the blood. Now see the circu-
lation of this fluid. The membranous bag gives a spas-
modic contraction at one end, and drives forward the
globules contained there; the contraction in an instant
passes onward along the three twists of the heart (the
part behind expanding immediately as the action passes
on), and the globules are forcibly expelled through the
narrow but open extremities. Meanwhile, globules from
around the other end have rushed in as soon as that part
resumed its usual width, which in turn are driven forward
by a periodic repetition of the systole and diastole.

The globules, thus periodically driven forth from the
heart, now let us watch and see what becomes of them.
They do not appear to pass into any defined system of
vessels that we may call arteries, but to find their way
through the interstices of the various organs in the gen-
eral cavity of the body.

The greater number of globules pass immediately from



BLOOD 49

the heart through a vessel into the short foot-stalk, where
they accumulate in a large reservoir; but the rest pass up
along the side of the body, which (in the aspect in which
we are looking at it) is the right As they proceed (by
jerks, of course, impelled by the contractions of the heart),
some find their way into the space between the breathing
surfaces, through narrow slits along the edges of the sac,
and wind along between the oval ciliary wheels, which we
will presently consider. Besides these, however, other
globules wind along between the outer surfaces of the
sac and the inner surface of the body-walls.

But to return to the current which passes up the right
side: arriving at the upper angle of the body, the stream
turns off to the left abruptly, principally passing along a
fold or groove in the exterior of the breathing-sac until it
reaches the left side, down which it passes, and along the
bottom, until it arrives at the entrance of the heart, and
rushes in to fill the vacuum produced by the expansion of
its walls after the periodic contraction. This is the per-
fect circle ; but the minor streams that had forked off side-
wise in the course, as those within the sac, for example,
find their way to the entrance of the heart by shorter and
more irregular courses

One or two things connected with this circulatory sys-
tem are worthy of special notice. The first is, that its di-
rection is not constant, but reversible. After we have
watched this course followed with regularity for perhaps
a hundred pulsations or so, all of a sudden the heart
ceases to beat, and all the globules rest in their circling
course that we had supposed incessant. Strange to be-
hold, after a pause of two or three seconds, the pulsation
begins again, but at the opposite end of the heart, and

r-SclENCE 3



50 EVENINGS AT THE MICROSCOPE

proceeds with perfect regularity, just as before, but in the
opposite direction. The globules, of course, obey the new
impulse, enter at their former exit, and pass out at their
former entrance, and perform their circulation in every
respect the same as before, but in the reverse direction.

Those globules that pass through the vessel into the
foot-stalk appear to accumulate there as in a reservoir, un-
til the course is changed, when they crowd into the heart
again and perform their grand tour. Yet there is a meas-
ure of circulation here; for even in the connecting vessel
one stream ascends from the reservoir into the body as the
other (and principal one) descends into it from the heart;
and so, vice versd.

I have spoken of these motions as being performed
with regularity; but, if you look closely, you will see
that this must be understood with some qualification. The
pulsations are not quite uniform, being sometimes more
languid, sometimes more vigorous; perhaps forty beats
in a minute may be the average; but I have counted
sixty, and presently after thirty; I have counted twenty
beats in one-half minute, and only fifteen in the next.
The period during which one course continues is equally
uncertain; but about two minutes may be the usual time.
Sometimes the pulsation intermits for a second or so, and
then goes on in the same direction; and sometimes there
is a curious variation in the heart's action a faint and
then a strong beat, a faint and a strong one, and so alter-
nately for some time.

The phenomena of respiration are so closely connected
with those of circulation that it is not at all malapropos to
turn from the latter to the former; not to say that it would
be high treason against scientific curiosity if I were to re-



BLOOD 51

move this object without explaining to you that marvel-
lous play of wheels that occupies the largest part of the
area that you behold. As you look on the globe, you
observe, hanging down from the upper extremity, and
reaching nearly to the bottom in one direction and almost
from side to side in another, a transparent square veil,
which is indeed a flat membranous bag, having its sides
pretty close together, with small openings along its edges,
and an orifice at the bottom leading into the stomach.

The mouth of this sac is in close connection with the
upper or principal orifice, and therefore receives the water,
which is constantly flowing in, while that aperture is ex-
panded. This fluid then bathes the whole interior of the
sac, but a portion of it escapes by the lateral openings into
the cavity of the body, between the sac and the mantle,
and is discharged through the secondary or side orifice.

The inner surface of this transparent sac is studded with
rings of a long oval figure, set side by side in four rows.
These rings appear to consist of a slight elevation of the
general membranous surface so as to make little shallow
cells, the whole edges of which are fringed with cilia,
whose movements make waves, that follow each other
round the course in regular succession. In truth it is a
beautiful sight to see forty or more of these oblong rings,
all set round their interior with what look like the cogs
on a watch-wheel, dark and distinct, running round and
round with an even, moderately rapid, ceaseless motion.
These black running figures, so like cogs and so well de-
fined as they are, are merely an optical delusion; they do
not represent the cilia, but merely the waves which the
cilia make; the cilia themselves are extremely slender
close-Bet hairs, as may be seen at the ends of the ovals,



52 EVENINGS AT THE MICROSCOPE

where a slight alteration of position prevents the waves
from taking the tooth -like appearance. Sometimes one
here and there of the ovals cease to play, while the rest
continue ; and, now and then, the whole are suddenly
arrested simultaneously as if by magic, and presently all
start together again, which has a most charming effect.
A still more singular circumstance is, that while in general
the ciliary wave runs in the same direction in the different
ovals, there will be one here and there in which the course
is reversed; and I think that the animal has the power of
choosing the direction of the waves, of setting them going
and of stopping them, individually as well as collectively.

The object of these ciliary wheels is to keep up a con-
stant current in the water. This fluid, as I have said,
enters from without, through the upper orifice of the body,
and is hurled over the whole surface of the breathing-sac
by means of the ciliary waves, parting with its oxygen, as
it goes, to the blood, which streams, as we saw, everywhere
between the rows of wheels. But the water has another
function: it carries particles of organic matter with it,
which are suitable for the nourishment of the creature;
these atoms are carried by the currents with the effete
water to the bottom of the sac, and are poured into the
stomach, where they are digested; the innutritive remains,
together with the waste water, being discharged through
the lateral orifice.

Thus we see how closely connected are the three car-
dinal processes of circulation, respiration, and digestion.



MOLLUSC A: THEIR SHELLS 63

CHAPTER III
MOLLUSCA: THEIR SHELLS, TONGUES, EYES, AND BARS

ONE of the most interesting aspects of microscopic
study is that in which it reveals the intimate
structure of objects, which to the unassisted eye



Online LibraryPhilip Henry GosseEvenings at the microscope (Volume 1) → online text (page 3 of 32)