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larger. In all, the extremity is drawn out to a lengthened
fine point, and is occupied with clear yellow cells, except



TIP OF SMALL HAIR OF MOUSE.



the very tip, which is colorless, and imbricated with sinu-
ous whorls, each consisting of a single scale.

But it is in the Bats that the imbricated character at-
tains its greatest development. On this slide is a number
of hairs from the fur of one of our English Bats, in which
it is far more conspicuous than in any example we have
yet seen. In the middle portion of each hair the scales lie
close, embracing their successors to the very edges, or
nearly; but the lower part, which is more slender, resem-
bles a multitude of trumpet-shaped flowers formed into
a chain, each being inserted into the throat of another.
The lip of the "flower" is generally oblique, and. here and
there we can perceive that each is formed of two half-
encircling scales; for one scale occasionally springs from
the level of its fellow, so as to make the imbrication
alternate.



EVENINGS AT THE MICROSCOPE



Even this, however, is far excelled by a species of Bat
from India, of whose hair I have now specimens on the
stage. The trumpet-like cups are here very thin and trans-
parent, but very expansive ; the diameter of the lip being,
in some parts of the hair, fully thrice as great as that of
the stem itself. The margin of each cup appears to be
undivided, but very irregularly notched and cut. In the
middle portion of the hair, the cups are far more crowded
than in the basal part, more brush-like and less elegant; and

this structure is continued to
the very extremity, which is
not drawn out to so attenu-
ated a point as the hair of
the Mouse, though it is of a
needle-like sharpness. The
trumpet-shaped scales are, it
seems, liable to be removed
by accident; for in these doz-
en hairs there are several in
which we see one or more
cups rubbed off, and in one
the stem is destitute of them
for a considerable space. The
stem so denuded closely resembles the basal part of a
Mouse's hair in its normal condition.

This character of being clothed with overlapping scales,
each growing out of its predecessor, is common, then, to
the hairs of the Mammalia, though it exists in different
degrees of development. ' It may be readily detected by the
unaided sense, even when the eye, though assisted by the
microscope, fails to recognize it. Almost every schoolboy
is familiar with the mode by which the tip of any hair may




HAIR OF BAT.



HAIR OP INDIAN BAT.



HAIRS, FEATHERS, AND SCALES 25



be distinguished from its base ; and even of the least
ment, the terminal end from the basal end. The initiated
lad assembles a few younger ones, and says, "Now you
may make a mark with ink on one end of a white horse-
hair, and I'll tell you, by feeling it, which end you have
marked. ' ' He does, infallibly. He rubs it to and fro be-
tween his thumb and finger, and the hair regularly travels
through in the direction of its base: one or two rubs of
course determine this, and the verdict is given oracularly
Now you see the cause of this property lies in the imbri-
cate structure ; the scales may be excessively thin and close,
but still they project sufficiently in any specimen to present
a barrier to motion in the terminal direction when pressed
between two surfaces, such as the fingers, while they very
readily move in the opposite.

But more than the success of a schoolboy's magic de-
pends on the imbricate surface of hairs. England's time-
honored manufacture, that which affords the highest seat
in her most august assembly, depends on it. The hat on
your head, the coat on your back, the flannel waistcoat
that shields your chest, the double hose that comfort your
ankles, the carpet under your feet, and hundreds of other
necessaries of life, are what they are, because mammalian
hairs are covered with sheathing scales.

It is owing to this structure that those hairs which
possess it in an appreciable degree are endowed with the
property of felting; that is, of being, especially under the
combined action of heat, moisture, motion, and pressure,
so interlaced and entangled as to become inseparable, and
of gradually forming a dense and cloth- like texture. The
"body," or substance of the best sort of men's hats, is

made of lamb's wool and rabbit's fur, not interwoven, but

15 SCIENCE 2



26 EVENINGS AT THE MICROSCOPE

simply beaten, pressed, and worked together, between damp
cloths. The same property enables woven woollen tissues
to become close and thick: every one knows that worsted
stockings shrink in their dimensions, but become much
thicker and firmer after they have been worn and washed
a little; and the " stout broadcloth," which has been the
characteristic covering of Englishmen for ages, would be
but a poor open flimsy texture, but for the intimate union
of the felted wool-fibres which accrues from the various
processes to which the fabric has been subjected.

In a commercial view, the excellence of wool is tested
by the closeness of its imbrications. When first the wool-
fibre was submitted to microscopical examination, the ex-
periment was made on a specimen of Merino ; it presented
2,400 serratures in an inch. Then a fibre of Saxon wool,
finer than the former, and known to possess a superior felt-
ing power, was tried: there were 2,720 serratures in an
inch. Next a specimen of South-Down wool, acknowl-
edged to be inferior to either of -the former, was examined,
and gave 2,080 serratures. Finally, the Leicester wool,
whose felting property is feebler still, yielded only 1,850
serratures per inch. And this connection of good felting
quality with the number and sharpness of the sheathing
scales is found to be invariable.

The hairs of many Insects are curious and interesting.
Here you may see the head of the hive-bee, which is mod-
erately clothed with hair; each hair is slender and pointed,
and is beset with a multitude of subordinate short hairs,
which project from the main stem, and stand out at an
angle: these are set on in a spiral order. Here again is
one of the hinder legs of the same bee: the yellow hair,
which you can see with the naked eye, consists of strong,



HAIRS, FEATHERS, AND SCALES 27

horny, curved spines, each of which is scored obliquely,
like a butcher's steel. These legs, are used, as you are well
aware, to brush off the pollen from the anthers of flowers,
wherewith the substance called bee-bread, the food of the
grubs, is made; and in this specimen you may see hun-
dreds of the beautiful oval pollen- grains entangled among
these formidable looking spines.

These rusty hairs are from a large caterpillar (that of
the Oak Egger Moth, I believe); they appear, when highly
magnified, like stout horny rods drawn out to an acute
point, and sending forth alternate short pointed spines,
which scarcely project from the line of the axis.

But there is scarcely any hair more curious than that
of a troublesome grub in museums and cabi-
nets, the larva of Dermestes lardarius, which
lives upon fur-skins, and any dried animal
substances. It has a cylindrical shaft, which
is covered with whorls of large close- set spines,
four or five in each whorl, closely succeeding
each other; the upper part of the shaft is sur-
rounded by a whorl of larger and more knotted
spines, and the extremity is furnished with six
or seven large filaments, which appear to have
a knob-like hinge in the middle, by which they
are bent up on themselves.

The feathers of Birds are essentially hairs. TIP OF HAIR or
That shrivelled membrane which we pull out
of the interior of a quill when we make a pen is the medul-
lary portion dried. There is a beautiful contrivance in
the barbs of most feathers, which I will illustrate by this
feather from the body- plumage of the domestic fowl.
Every one must have observed the regular arrangement




28 EVENINGS AT THE MICROSCOPE

of the vane of a feather, and the exquisite manner in
which the beards of which it is composed are connected
together. This is specially observable in the wing- feathers
a goose- quill, for example; where the vane, though very
light and thin, forms an exceedingly firm resisting me-
dium, the individual beards maintaining their union with
great tenacity, and resuming it immediately, when they
have been violently separated.

Now this property is of high importance in the econ-
omy of the bird. It is essential that with great lightness
and buoyancy for the bird is a flying creature there be
power to strike the air with a broad resisting surface. The
wide vanes of the quill- feathers afford these two requisites,
strength and lightness; the latter depending on the material
employed, which is very cellular, and the former on the
mode in which the individual barbs, set edgewise to the
direction of the stroke, take a firm hold on each other.

Now, in the body-feather which is under the microscope
we see that the central stem carries on each side a row of
barbs, which interlock with each other. The magnifying
power shows us that these barbs are not simple filaments,
but are themselves doubly bearded in the same fashion;
and further, that these barbules of the second series are
furnished with a third series. It is in this third series of
filaments that the tenacity in question resides. If we iso-
late one of the primary beards, by stripping away a few on
each side of it, and again put it on the stage, we see that
the secondary barbules of one side are armed differently
from those of the other side. Those of the lower side carry
short and simple barbulets, whereas those of the side which
looks toward the point of the feather bear much longer
ones; and, moreover, many of them are abruptly hooked



HAIRS, FEATHERS, AND SCALES



29



backward. Now, whenever the primary beards are brought
into contact, some of these hooks catch on the barbule next
above, and, slipping into the angles formed by the barbu-
lets, hold there, and thus the two contiguous beards are
firmly locked together.

In the beard of the goose-quill, the structure is essen-
tially the same, but the barbulets are far more numerous
and more closely set; they are also proportionally much





BARB OF CLOTHING-FEATHER OP FOWL.



BARB FROM GOOSE-QUILL.



larger both those which are hooked and those which are
simple. Indeed, the latter manifest a tendency to the
hooked form, and by all these peculiarities the interlock-
ing power is augmented. It is interesting to observe the
great dilatation of the beard in a direction toward the infe-
rior surface of the feather toward the stroke, as I just now
observed. This is to increase the resisting power, as a thin
board set edgewise will bear a great weight without bending
or breaking, provided it can be kept from yielding laterally,



30 EVENINGS AT THE MICROSCOPE

The barbules are arranged only on the very edge the upper
edge of the beard.

. We will now examine some specimens of scales of Fishes,
all of which are very interesting and beautiful objects under
low powers of the microscope; though higher powers are
requisite to resolve their structure. We will use both.

The scales of almost all the Fishes with which we are
familiar fall under two kinds, which have been named
ctenoid (or comb-like), and cycloid (or roundish). The
Perch affords us good examples of the former kind. On
this slide are three scales from the body of this fish: the
one on the left side is taken from the back (Fig. a);




SCALES OF PERCH.



the middle one from the lateral line (6); and the one on
the right from the belly (c). In order to understand these
objects we must remember that the scales of fishes are horny
or bony plates, developed in the substance of the proper
skin, with a layer of which they are always covered. In
most cases (as, for example, the Perch), the hinder end of
each scale projects, carrying with it the thin layer of skin
with which it is invested; and thus the scales overlay one
another, like the tiles of a house, or like the feathers of a
bird, and that for a like purpose. For as the rain, falling
on the house-top, has a tendency to flow downward, from
gravitation ; and, as the slope of the roof is in that direction,



HAIRS, FEATHERS, AND SCALES 31

the current passing over each tile is deposited from its bot-_
tom edge on the middle of the next one, whence it still flows
down to the free edge of this one, and so in succession. So
the motion of the bird through the air, and of the fish
through the water, produces the very same effect as if these
fluids were in motion and the animals were still; and there-
fore the bodies of the latter are, as it were, tiled with feath-
ers or scales, the free edges of which, looking in the oppo-
site direction to the coming of the current (that is, the same
direction as its flow), deposit the successive particles of the
moving fluid in the midst of the successive feathers or scales.
Thus two results ensue, both essential to the comfort of the
animal: first, the air or water does not run upward between
the feathers or scales to the skin; and, secondly, the stir-
face presents no impediment to free motion. This latter
advantage will be appreciated, if you take hold of a dead
bird by the legs, and push it rapidly through the air tail-
foremost: the feathers will instantly rise and ruffle up,
presenting a powerful resistance to movement in that
direction.

These scales of the Perch have their hinder, or free
edge, set with fine crystalline points, arranged in succes-
sive rows, and overlapping. Their front side is cut with
a scalloped pattern, the extremities of undulations of the
surface that radiate from a common point behind the cen-
tre. These undulations are separated by narrow furrows,
across which, contrary to the ordinary rule, the close-set
concentric lines that follow the sinuosities of the outline
are not visible. Under the microscope they look as if they
had been split in these radiating lines, after the whole num-
ber of layers had been completed, and the fissures had then
been filled with new transparent substance.



32



EVENINGS AT THE MICROSCOPE



The middle scale is, as I have said, from the lateral line.
Along each side, in most fishes, may be observed a line,
known as the lateral line, formed by scales of peculiar form.
They are commonly more bony than the other scales, and
are pierced by a tubular orifice for the escape (as is gener-
ally supposed, though this has been denied) of a mucous
secretion, which is poured out from glands beneath, and
thus flows over the body for the double purpose of pro-




SCALES OF GOLD-FISH.



tecting the skin from the macerating influence of the sur-
rounding water, and of diminishing friction in swimming.
Let us now look at some scales of the cycloid kind. The
great majority of our fishes are clothed with such as are of
this description. This dead Gold-fish shall give us exam-
ples. The three scales in the upper row are from the lateral
line, the left-hand one (a) taken just behind the head, the
second (b) near the middle of the body, and the right-hand
one (c) near the tail. Of the lower row, the first (d) is from
the back, the second (e) from the middle of the belly, and



HAIRS, FEATHERS, AND SCALES 33

the last (/) from the throat. Thus we see there is consid-
erable variety in form presented by the scales even of the
same individual fish. They all, however, differ from those
of the Perch in this respect: that their free overlapping
edges are entire, or destitute of the crystalline points which
we saw in the former examples; while they agree in having
the front edges, by which they are during life imbedded in
the skin, cut into waves or sinuosities. The lower part, as
we now look at them, is the free portion of each, which
alone is visible in the living fish, the other parts being
concealed by the three neighboring scales that overlap it
above, in front, and below.

In those from the lateral line, the tube already referred
to is seen to pervade each, running through it longitudi-
nally, so that it opens posteriorly on the outer surface, and
anteriorly on the inner or under surface of the scale. In
the scales near the front of the line, just behind the head,
the tube is large and prominent (a), while in the scales
at the opposite extremity it becomes slender; diminishing,
in the very last scale viz., at the commencement of the
tail-fin to a mere groove.

The whole surface of each scale, when viewed under a
lens of low power, is seen to be covered with concentric
lines, following the irregular sinuosities of the outline.
These lines are the edges of the successive layers of which
the scale is believed to be composed, each layer being added
in the process of growth to the under surface, and each be-
ing a little larger every way than its predecessor; thus the
scale is a very depressed cone, of which the centre is the
apex. There is a marked difference (indicated in the fig-
ures) between that part of the surface which is exposed,
and that which is covered by the other scales; the concen-



34 EVENINGS AT THE MICROSCOPE

trie marks in the former are much coarser and less regular,
often being interrupted, and seeming to run into each other,
and frequently swelling into oval scars. This may, per-
haps, be owing to the surface having been partially worn
down by rubbing against the gravel of the bottom, or against
other objects in the water. Besides the concentric lines,
there are seen on many o~f the scales, especially those of the
lateral line, radiating lines varying in number from one to
twenty, or more, diverging from the centre toward the cir-
cumference, and frequently connected by cross lines form-
ing a sort of net-work around the centre (see c). Under
the microscope, these lines appear to be elevated ridges,
dividing the concentric lines; but of their use I am ignorant.
What I have just stated is the ordinary explanation
of these fine concentric lines; but a careful examination of
the structure with much higher powers than we have been
using induces me to doubt its correctness. Eeverting to the
scales of the Perch, let us notice the clear diverging bands,

which look as if the whole
scale had been split in sev-
eral places, and the openings
thus made filled with uniform
clear substance. The same
structure is seen in many other
scales, as in this cycloid one
from the Flounder, which, be-
OF FLOUNDER. ing coarsely lined, shows the

a, Natural size. . n

structure well; or in these

from the Green Wrasse. I will now apply to one of these
a power of 600 diameters, concentrating the light thrown
through the scale from the mirror by the achromatic con-
denser, and examine the scale anew. You now see two




HAIRS, FEATHERS, AND SCALES 35

distinct layers; the upper one which bears the concentric
lines, and a lower clear one which not only fills the radiat-
ing bands, but underlies the whole of the lined parts. The
concentric lines of the upper layer do not now appear to
be edges of successive plates, but irregular canals running
through the solid substance. This, however, is illusory:
for, by delicate focusing, we perceive that each portion
marked by these lines is really in a different plane from
the others, that the highest is at the centre of radiation of
the scale, and that each is successively lower till we reach
the margin. But now, if with very sharp scissors we cut
one of these scales longitudinally through the centre, and
examine the cut edge, we find that each of these lines
forms a distinct ridge. On the other hand, the under layer
of clear substance is quite smooth, and always a little ex-
ceeds the margin of the concentrically lined portion. The
clear substance that fills the radiating slits agrees both in
texture and level with this lower layer, and is manifestly
continuous with it.

Hence, I think that, in these slit scales, the upper layer
is formed, as commonly believed, by successive deposits
from beneath; but that, after a few have been deposited,
they begin to slit, probably by contraction in becoming
solid ; that the lower layer is formed after each upper one
is hardened, exceeding its length by a little, and filling up
the slit; that this lower layer becomes the upper layer of
the next course, slitting, and turning up its terminal edge
as it hardens; that then the lower layer is deposited on
this, filling up the slit as before; and that this process
goes on as long as the fish lives.

It is curious that, in the scales of the Pike, the por-
tions thus separated by slitting, instead of expanding and



36 EVENINGS AT THE MICROSCOPE

leaving spaces to be filled up, actually close over each
other, the divided parts overlapping considerably, as you
may see in these specimens. The left-hand scale (a) is
from the back ; the central one (ft), which has only a deep
narrow incision instead of a tube, is from the lateral line;
and the third (c) is from the belly of the fish.

Let us return now to the scales of our Gold-fish, and
examine a highly interesting structure connected with them.
The brilliant golden or silvery reflection that constitutes
the beauty of these lovely fishes depends not on the scales
themselves, but on a soft layer of pigment spread over




SCALES OF PIKE.



their inner surface, and seen through their translucent sub-
stance. On carefully detaching a scale, we see on the un-
der side, opposite to that portion only which was exposed
(all the concealed parts being colorless), a layer of soft
gleaming substance, easily separable, either silvery or
golden, according to the hue of the fish. If now we re-
move a small portion of this substance with a fine needle,
and spread it on a plate of thin glass, we shall find, by
the aid of the microscope, that it consists of two distinct
substances; the one giving the color, the other the metal-
lic lustre. With a power of 300 diameters, the former is
seen to be a layer of loose membranous cells of an orange
color, in what are properly called the Gold-fishes, and




HAIRS, FEATHERS, AND SCALES 37

whitish or pellucid in the Silver-fishes. If we now add
a minute drop of water to the mass, and gently agitate it
with the point of a needle, and again submit it to the mi-
croscope, we shall have a beautiful and interesting spec-
tacle. The water around the mass is seen to
be full of an infinite number of flat spicula
or crystals, varying much in size, but of
very constant form, a flat oblong prism
with angular ends (as represented in the
accompanying engraving). By transmitted
light they are so transparent and filmy as
to be only just discernible; but by reflected
light, and especially under the sun's rays, they flash like
plates of polished steel. But what appears most singular
is that each spiculum is perpetually vibrating and quiver-
ing with a motion apparently quite spontaneous, but prob-
ably to be referred to slight vibrations of the water in
which they float; and each independently of the rest, so
as to convey the impression to the observer that each is
animated with life, though the scale be taken from a fish
some days dead. Owing to this irregular motion, and con-
sequent change of position, each spiculum, as it assumes
or leaves the reflecting angle, is momentarily brightening
or waning, flashing out or retiring into darkness, produc-
ing a magic effect on the admiring observer. To this
property, I suppose, is to be attributed the beautiful
pearly play of light that marks these lovely fishes, as
distinguished from the light reflected by a uniformly pol-
ished surface. I have found the pearly pigment of the
scales to be provided with similar spicula in fishes widely
differing in size, structure, and habits; as the Gudgeon and
Minnow, the Pike and the Marine Bream. The spicula of



38 EVENINGS AT THE MICROSCOPE

these fishes agree in general form with those of the Gold-
fish; and also in size, with the exception of trifling vari-
ations in the comparative length and breadth. The col-
oring matter is lodged in lengthened cylindrical cells,
arranged side by side, and running across the scale; that
is, in a direction at right angles to the lateral line.



CHAPTER II

BLOOD

THE microscope is daily becoming a more and more
important aid to legal investigation. An illustra-
tion of this occurred not long ago, in which a mur-
der was brought home to the criminal by means of this
instrument. Much circumstantial evidence had been ad-
duced against him, among which was the fact, that a knife
in his possession was smeared with blood, which had dried
both on the blade and on the handle. The prisoner strove



Online LibraryPhilip Henry GosseEvenings at the microscope (Volume 1) → online text (page 2 of 32)