[Illustration: Plate I.
_London, John Van Voorst._]
AN
ELEMENTARY TEXT-BOOK
OF
THE MICROSCOPE;
INCLUDING A DESCRIPTION OF THE METHODS OF
PREPARING AND MOUNTING OBJECTS, ETC.
BY
J. W. GRIFFITH, M.D., F.L.S., ETC.,
MEMBER OF THE ROYAL COLLEGE OF PHYSICIANS; CONJOINT AUTHOR OF
THE MICROGRAPHIC DICTIONARY, ETC.
WITH TWELVE COLOURED PLATES,
CONTAINING 451 FIGURES.
[Illustration]
LONDON:
JOHN VAN VOORST, PATERNOSTER ROW.
MDCCCLXIV.
[_The right of translation is reserved._]
PREFACE.
The object of this little work is to furnish an elementary course of
instruction in the use of the Microscope, and on its application to the
examination of the structure of plants and animals. Assuming that the
reader has had no previous acquaintance with the Microscope, or with the
study of natural history, I have attempted to render the descriptions of
the objects as simple as possible. At the same time, the technical terms
have been added and explained, in order gradually to render them
familiar to the reader, and thus facilitate the future study of larger
and more detailed works. The objects figured and described comprise the
principal structures and more minute forms of both the vegetable and the
animal kingdom, those having been selected which are common and readily
procurable.
A chapter has been given upon the optical principles on which the
action of the instrument depends (which will assist the reader to
understand the operation of its constituent parts), including a sketch
of the subject of polarized light. The order in which the subjects are
treated is scientific, and particular directions have been given for the
examination of the objects.
The small size of the work has necessitated the exclusion of figurative
descriptions, so that it is adapted rather for a worker than a reader;
at the same time, the matter forms a course, and must be taken as a
whole for the proper comprehension of the subjects. The technical terms
used are referred to in the Index, so as to furnish to some extent a
glossary of terms; and their derivation is given, to facilitate their
recollection. The figures, with very few exceptions, are drawn from
nature, and are coloured that the objects may be more easily recognized.
The magnifying powers under which they have been drawn are denoted by a
small number placed beneath each figure: and the particular attention of
the reader is requested to this point; otherwise the whole subject will
be utterly confused; so much does the appearance of objects vary under
different powers.
Directions are given for preparing and mounting objects, implying that
the reader will collect specimens for himself, which is to be strongly
recommended as the best method of acquiring a practical and useful
acquaintance with the objects. These will serve to furnish permanent
landmarks in the great ocean of structural forms, will probably recall
in after-years pleasant recollections of early excursions in search of
the beauties of nature, and, surely, deepen the conviction of the
existence of their All-wise Creator.
J. W. G.
CONTENTS.
CHAP. PAGE
I. THE MICROSCOPE 1
II. THE MOUNTING OF OBJECTS 10
III. VEGETABLE ELEMENTS AND TISSUES 19
IV. VEGETABLE ORGANS 31
V. FERNS 49
VI. MOSSES 54
VII. ALGÆ 64
VIII. LICHENS 91
IX. FUNGI 96
X. ANIMAL ELEMENTS AND TISSUES 113
XI. ARTICULATA 127
XII. RADIATA 153
XIII. PROTOZOA 155
XIV. OPTICAL PRINCIPLES 167
PLATE I. [FRONTISPIECE.]
VEGETABLE TISSUES, &c.
Fig.
1. Leaf of Geranium: cells, chlorophyll, and intercellular passages.
2. Cells of Apple.
3. Starch-granules: _a_, of Wheat; _b_, of Arrowroot; _c_, of Potato;
_d_, of Oat; _e_, of Lentil; _f_, of Rice.
4. Cells of Potato, containing Starch.
5. Garden Rhubarb-stalk: _a_, raphides; _b_, reticulated duct; _c_,
spiral vessel; _d_, woody fibre; _e_, annular vessel.
6. Wood-cells from stem of Chrysanthemum.
7. Deal, transverse section: _a_, glandular tissue; _b_, woody fibre.
8. Deal, longitudinal (radial) section of glandular tissue.
9. Deal, longitudinal section of woody fibre.
10. Deal, tangential section.
11. Holly, wood of: _a_, porous cells; _b_, _d_, _e_, wood-cells; _c_,
dotted ducts.
12. Hairs, vegetable: _a_, _b_, of Groundsel; _c_, of London Pride; _d_,
_e_, of Geranium; _f_, of Chrysanthemum.
13. Epidermis of Geranium-leaf.
14. Style of Crocus, with pollen-granule and-tube.
15. Pollen-grain of Crocus, with pollen-tube.
16. Pollen of Primrose.
17. Pollen of Sunflower.
18. Pollen of _Convolvulus major_.
19. Caraway-seed.
20. Needle-point.
21. Sting of Nettle.
22. Hair of Spiderwort.
23. Hair of Spiderwort, single cell.
24. Epidermis of Geranium-petal.
25. Petal of Chickweed.
26. Sepal of Chickweed.
27. Seed of Poppy.
28. Epidermis of _Deutzia_.
29. Seed of Mignonette.
30. Pollen of Chickweed, dry.
31. Pollen of Chickweed, in water.
32. Flower of Chickweed.
33. Epidermis of petal of Chickweed.
34. Hairs of calyx of Chickweed.
35. Hairs of seed of _Collomia_.
36. Stem of Dicotyledon, section of.
37. Stem of Monocotyledon, section of.
38. Seed of Shepherd’s Purse, transverse section.
39. Stamen of Chickweed.
40. Stigma of Chickweed.
41. Ovary of Chickweed.
42. Leaf of Chickweed.
43. Seed of Wallflower, section of.
44. Seed of Wallflower, radicle and cotyledons.
45. Embryo-sac of Chickweed.
46. Embryo-sac of Chickweed.
47. Embryo-sac of Chickweed.
48. Wheat, cotyledon and leaves of, section.
49. Mustard-seed, cotyledons and radicle.
50. Mustard-seed, transverse section.
51. Chickweed, seed of.
52. Seed of _Eccremocarpus scaber_.
53. Grain of Wheat: _a_, cotyledon; _b_, embryo; _c_, radicle; _d_,
albumen.
54. Ovule of Wallflower.
55. Cotyledons of Chickweed.
56. Plum-stone, section of.
A
TEXT-BOOK
OF
THE MICROSCOPE.
CHAPTER I.
THE MICROSCOPE.
The microscope (from μικρὁς, little, and σκοπέω, to see), so called
because it enables us to see objects which are too small to be seen with
the naked eye, consists of several parts, each of which has its special
use. As the proper management of these is of great importance in the
successful application of the instrument to minute investigations, we
shall commence with the consideration of their names and uses, including
those of the more important pieces of accessory apparatus.
_Microscope._--The foot of the microscope is that part which supports
the instrument upon the table; it is connected above with the stand, of
which it is often considered a part. The stand sometimes consists of a
single rod or pillar; but in the best microscopes it is composed of two
upright plates, between which, at the upper part, the rest of the
microscope swings stiffly upon an axle. Arising from this axle,
indirectly through the medium of parts which require no special mention,
is an arm, to which the body is fixed. The body is moveable up and down
by one or two large milled heads, connected with a grooved rod or
pinion, which works in the teeth of a rack fixed to the back of the
body, or of the arm which supports the body. The large milled heads form
the “coarse movement,” as it is called.
On the top of the arm, or on the front and lower part of the body of the
microscope, is placed the “fine movement,” consisting of a small milled
head, with a fine screw, for moving the body through very small
distances.
Next is the “stage,” or flat plate, upon which the objects to be viewed
are placed. This is often so arranged that, by turning two milled heads,
the object can be moved backwards and forwards, or from side to side; it
is then a “moveable stage.”
The eye-piece slides into the upper end of the body; and the
object-glass screws into its lower end.
Beneath the stage is the mirror, which reflects the light through the
object, the object-glass, and eye-piece to the eye.
_Object-glasses._--The object-glasses are the most valuable parts of the
instrument. There are generally three or more of them; and, by means of
an “adapter,” any object-glass can be made to fit any microscope. Great
care is required in their use, especially to avoid scratching the lower
surface of the glass, which is sometimes accidentally done by pressing
the surface against any hard body, or allowing such a body to fall upon
it. When not in use, the object-glasses should either be put away in the
brass boxes or covered with a small bell-glass, to prevent their
receiving any injury.
The object-glasses possess various magnifying powers, according to the
distance at which they require to be placed from the object for distinct
vision: this is not, however, absolutely correct, yet may serve as a
general expression. Thus we have a 1-inch, ½-inch, ¼-inch object-glass,
&c. The object-glasses, for brevity, are often called powers.
As a beginner may at first have some difficulty in distinguishing a high
from a low power, it may be remarked that the size of the lower glass is
larger the lower the power: but, in the case of the better
object-glasses, the focal distance is engraved on the box in which the
object-glass is packed when put away.
As the coarse movement raises or depresses the body and object-glass
through comparatively large distances, it must be used only with the
lower object-glasses, _i. e._ those of low or little magnifying power,
as the 2-inch, 1-inch, or ½-inch, or to bring the object-glass near the
focal distance with the higher powers; whereas the fine movement serves
to adjust the higher powers, as the ¼-inch, &c.
If the object-glasses should become soiled on the lower face, this
should be wiped very gently with an old silk handkerchief or piece of
very soft wash-leather, previously shaken to displace dust. The same
method will answer to cleanse the upper surface of the eye-piece.
Great care must be taken that a slide which has been warmed in any
experiment be not placed near the object-glass until quite cold.
_Mirror._--The mirror has sometimes one silvered face only, at others
two--one flat, the other concave. The flat surface is used to reflect
the light upon the object when the light is too great with the concave
surface.
Beneath the stage, in most microscopes, is a circular moveable
“diaphragm,” perforated with holes of various sizes, to allow more or
less of the light reflected by the mirror to pass through, as may be
required.
When opake objects are viewed, the mirror should be turned aside, so as
not to reflect any light through the stage.
_Eye-pieces._--With all microscopes, two or more eye-pieces are
supplied. These possess different magnifying powers, and are lettered or
numbered accordingly; the lowest power with the earliest letters of the
alphabet, or with the smallest numbers, thus: A, B, C; or 1, 2, 3, &c.
_Forceps._--These are fine pincers, for holding minute bodies to be
viewed as opake objects. In use, they are inserted by a stem connected
with a joint, in an aperture, generally in the stage; and are moveable
in all directions.
_Live-box._--This is a brass slide, perforated in the middle, to the
aperture in which is soldered a short piece of brass tube, closed at the
top with a circular plate of thin glass. A rather wider and longer piece
of brass tube slides over the former; this is also closed at the top by
a thin glass plate, so as to allow of an object being confined or
compressed between the two glass plates. It is used for examining living
objects in water.
_Knife, &c._--For cutting slices or sections of objects, a very sharp
knife with a thin back will be found useful; or a razor may be used for
the same purpose. And for picking minute objects to pieces, or
dissection, fine needles, cut off short with pliers, the blunt ends
being thrust into hair-pencil sticks, will be requisite.
A pair of fine surgical forceps will also be required, for taking up
minute objects. These should be without teeth, and the spring-action so
weak that the points can be very easily approximated.
_Dipping-tubes._--For removing minute objects from water, two or three
narrow glass tubes, of different lengths, are very useful. These are
called “dipping tubes,” and are used thus:--the tube being held upright
between the second finger and the thumb, the fore finger is placed at
the top of the tube to close it; the tube is then put into the water
until the lower end is close to the object, when, on suddenly removing
the fore finger, the water will rise in the tube, carrying the object
with it. The fore finger is then again applied to the tube, and, as thus
held, the water will not run out. The tube is then held over a
watch-glass, or a slide, upon which the water and object will fall on
removing the fore finger.
A small glass spirit-lamp will be found very useful. The spirit for
burning should be methylated alcohol, or wood-naphtha. As these spirits
are inflammable, great care should be taken to keep the stock-bottle
away from a candle or other flame, when filling the lamp.
_Achromatic condenser._--A very important piece of apparatus, when high
powers are used, is the achromatic condenser; it is not, however,
usually supplied with the cheaper microscopes. It consists of a brass
fitting, placed beneath the stage, into which an object-glass is
screwed, in an inverted position, _i. e._ the small end of the
object-glass being placed uppermost. It serves to condense the light to
a focus upon the object, so as to illuminate it more brightly; and as it
can be elevated or depressed by a milled head and rack-work, the object
can be viewed by either converging or diverging rays.
_Simple microscope._--For examining the larger kinds of objects, and for
dissection, a simple microscope is very useful. This consists of a
stand, a stage, and an arm supporting a simple lens or combination of
lenses, but without the body of the compound microscope (as the ordinary
microscope is distinctively called). For most purposes, common
plano-convex or doubly convex lenses are sufficient to form the
object-glasses of a simple microscope. With the best microscopes, an
“erector,” or tube containing a pair of lenses, fitted within the body,
renders the compound microscope capable of answering most of the
purposes of a simple microscope.
_Polariscope._--An expensive but interesting and useful addition to a
microscope is a polarizing apparatus, or polariscope. This consists of a
Nicol’s prism, or a plate of tourmaline, placed beneath the stage, and
another in the body of the microscope or above the eye-piece; both in
brass fittings. The former is called the polarizer, and the latter the
analyzer.
_Rotating disk._--Another most useful piece of apparatus, for moving
opake objects whilst under the microscope, in all directions, is Smith
and Beck’s “rotating disk.”
_Slides._--The slides upon which objects, especially those to be viewed
as transparent objects, are to be placed, should be made of crown or
plate glass. They are usually 3 inches long, and 1 inch wide; but I
prefer them 2½ inches long, and 1 inch wide, simply because they take up
less room in a cabinet, and because they do not project beyond the stage
on either side. They should not be more than 1/20th of an inch thick,
and as colourless and clear as possible. The edges should be ground or
filed, to prevent their scratching the stage.
_Covers._--The covers are square pieces of very thin glass, less in
breadth than the slides, so as not to reach their margins; and of
various thicknesses, the thicker and stronger being used to cover large
objects for examination under the lower powers, and the thinner serving
to cover very delicate objects requiring the higher powers.
_Side condenser._--For illuminating opake objects, a large plano-convex
or doubly convex “bull’s-eye” lens, or side condenser, is used; this is
fixed to an arm, which slides on a stand, so as to be capable of being
raised or lowered to a suitable height. This is placed between the
source of light and the stage, and at such a distance from the latter
that the light may be brought to a focus upon the object. Sometimes a
“Lieberkuhn” or concave silver reflector is used for this purpose.
These are the most important pieces of apparatus required in examining
microscopic bodies. But the beginner will do well, if he have the
achromatic condenser and the polarizing apparatus, to lay these aside
until he has had considerable practice in examining objects simply with
the mirror and the lower powers.
_General method of observation._--In the ordinary use of the microscope,
the object to be examined is laid upon the middle of a slide, which is
placed upon the stage. The object is then brought under the centre of
the object-glass, the mirror inclined half towards the light and half
towards the object, until the object is seen to be illuminated, when,
upon looking through the eye-piece and adjusting the coarse and fine
movements, the object as it comes into focus will be seen, as it were,
drawn upon a white disk, which is called the “field.”
When the object is wet, it cannot be viewed without the application of a
cover, because the water evaporates and condenses upon the under surface
of the object-glass.
To avoid the danger of injuring the object-glass, or crushing the object
by lowering the body and object-glass too much in adjustment to focus,
the best plan is to lower the body by means of the coarse movement until
the object-glass appears near the object to the eye placed on one side
of the stage, and then to apply the eye to the eye-piece, and turn the
milled head so as to raise the body and object-glass until the object is
brought into focus.
In the examination of an object, it is best to begin with a low power,
so as to obtain a view of the general arrangement of its parts, and
then to apply the higher eye-pieces and powers, so that the more minute
structural details may be observed.
_Illumination._--The illumination or proper management of the light in
using the microscope is of very great importance. The best light,
especially with the low powers, is daylight, particularly that reflected
from white clouds; this is least injurious to the eyes. But as daylight
cannot always be used for microscopic investigations, and as cloud-light
is insufficient with the higher powers, some kind of artificial light
must be supplied. That mostly used is the light of a reading oil lamp or
of a gas-burner, a candle being quite useless, on account of the
flickering of the flame with the slightest draught. A moderator lamp has
the defect of too great height; otherwise this would be better than any
other oil lamp. A powerful and excellent light for the highest powers is
afforded by a short paraffine-oil lamp.
As intently looking at strongly illuminated objects is injurious to the
sight, the amount of light allowed to pass the diaphragm should be no
more than is agreeable, and sufficient to show the object distinctly.
In using the higher powers, the field is much less bright with the use
of the same light than in the case of the lower powers; and difficulty
is often found in obtaining sufficient light for the distinct vision of
the object. The achromatic condenser is of most important service here;
but it is sometimes requisite, even when this is used, to condense the
light upon the mirror by a shallow bull’s-eye; or a large common
metallic reflector may be used for the same purpose.
The most convenient manner of proceeding in regard to the use of the
individual eyes is to apply the left eye to the eye-piece, so that the
right eye may be used in finding the stage-movements, or in moving the
slide, without removing the eye from the eye-piece. If this arrangement
be adopted, the light should be placed towards the left-hand side of
the microscope. But the best way to avoid injuring the sight would be to
use both eyes for viewing the objects in turn, although most microscopic
observers make use of one eye only for this purpose.
The structure of many transparent objects can be best seen when the
mirror is turned more or less obliquely to one side, so as to view them
by oblique light, as it is called: we shall refer to this point
hereafter.
As a rule, objects are best seen by transmitted light, or as transparent
objects, although it is well to examine objects under both kinds of
illumination, _i. e._ by transmitted and reflected light.
If during the use of the microscope, after removing the eye from the
instrument, the impression of the light remains perceptible to the
sight, the light used has been too strong, or its action too long
continued; and the instrument should be at once laid aside for a time.