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6
/A
HALF-HOUKS WITH THE MICEOSCOPE.
~-^ ***: *
PI. IX
HALF- HOURS
THE MICROSCOPE;
BEING A POPULAR GUIDE TO THE USE OF THE MICROSCOPE AS
MEANS OF AMUSEMENT AND INSTRUCTION.
BY EDWIN LANKESTER, M.D.
ILLUSTEATED FEOM NATUEE,
BY
TUFFEN WEST.
.A. 3ST IE "W IE X> I T I O IsT.
With Chapter on the Polwriscope by F. Kitton.
NEW YORK :
G. P. PUTNAM'S SONS,
FOUETH AVENUE AND TWENTY-THIED STEEET.
1874.
CONTENTS,
CHAPTER J.
PAGE
A HA.LF-HOI7JI ON THE STRUCTURE OF THE MICROSCOPE 1
CHAPTER II.
A HALF-HOUR WITH THE MICROSCOPE IN THE GARDEN 30
CHAPTER III.
A HALF-HOUR WITH THE MICROSCOPE IN THE COUNTRY 47
CHAPTER IV.
A HALF-HOUR WITH THE MICROSCOPE AT THE POND- SIDE $6 %
CHAPTER Y.
A HALF-HOUR WITH THE MISCROSCOPE AT THE SEA-SIDE 6? ,
CHAPTER VI.
A IIALT-.HOUR WITH THE MICROSCOPE IN-DOORS 78
CHAPTER VII.
A HAIF-HOUR WITH POLARIZED LIGHT
APPENDIX.
THE PREPARATION AND MOUNTING OF OLJECTS
I 2
DESCRIPTION OF PLATES.
In the examination of these Plates the observer is
requested to remember that they are not all drawn to
the same scale. Some objects, adapted for low powers,
are only magnified a few times, whilst smaller objects
are magnified many Jiundred times. All objects, of
course, vary in apparent size, according to the powers
with which they are examined. Descriptions of the
objects will be found in the pages indicated.
PLATE I. to face page 1.
FIO. PAGE
1. Vegetable cells with, nucleus from apple 31
2. 'Cellular tissue from pith of elder 31
3. Stellate cell-tissue from rush 32
4. Flat tabular cell from surface of tongxie 91
5. Ciliated cell from windpipe of calf ?1
€. Human blood corpuscles 91
7. Blood corpuscles from fowl 92
8. Blood corpuscle from frog 92
9. Blood corpuscle from sole , 92
10. Blood corpuscle from beetle 92
11. Filament of a species of Zygnema, a plant 60
a. Portion of a filament of the same, the cell-
contents becoming changed into zoospores.
&, Zoospore more highly magnified.
X THE MICROSCOPE.
FJO, PAGE
12. Filament of a species of OsciUatoria, a plant .... 60
a. Portion more highly magnified.
] 3. Pandorlna Morum, a plant 60
14. Volvox Globator, a plant 60
15. Englena viridis, a plant, showing various forms
which it assumes 61
18o Amoeba, an infusory animalcule 69
a, b, c, show the various forms which thi-3 ani-
malcule assumes
17. Actinoplirys Sol, the sun animalcule 62-60
18. Difflugia, an infusory animalcule 63
19. Arcella, an infusory animalcule , 63
20. Lagena, a species of Foraminifer 69
21. Polystomella crispa, a species of Foraminifer 69
22. Gldbigerina, a species of Foraminifer 69
23. Rosalina, from chalk, a Foraminifer 69
24. Living Rosalina, a Foraminifer C9
25. Texlilaria, a species of Foraminifer QQ
PLATE II. to face page 32.
26. Uha in different stages of development , , ., gj
a. Cells in single series.
J. Commencement of lateral extension.
c. Portion expanded.
27 Cosrnarium, a species of Desmid undergoing self-
division.
28. Eaaslrum, a species cf Desmid 57
29. Closterium, a species of Desmid « . t 57
a. Undergoing self-division.
£0. D&midium, a species of Desmid v ... 57
DESCRIPTION OF PLATE3. xi
FIG. PAGE
31. Pediastrum, a species of Desmid 57
32. Scencdcsmus, a species of Desmid , . . . . 57
S3. Surlrella nobilis, a species of Diatom 59
34. Pinnularia viridis, a species of Diatom 59
35. a. Navicula, a species of Diatom undergoing self-
division
&. Front view of the same.
36. Melosira varians, a species of Diatom 59
37. Melosira nummuloides undergoing self-division . ... 59
38. Coscinodiscus eccentricus, a species of Diatom 58
39. Paramecium Aurelia, an iufusory animalcule 64
40. Vorticella nebulifera, an infusory animalcule 63
41. Rotifer vulgaris, a wheel animalcule 65
42. Stomates on a portion of cuticle of hyacinth leaf .. 32
43. Sinuous walled cells and stomates from under sur-
face of leaf of water-cress 32
44. Cuticle of wheat straw with stomates 33
45. Cuticle from petal of geranium (Pelargonium). ... 33
46. Cuticle from leaf of a species of aloe 33
47. Spiral vessel from leaf-stalk of garden rhubarb .... 35
48. Ditto unrolled 35
49. Annular vessel from wheat root 35
50. Dichotomous spiral vessels 35
51. Dotted duct from common radish * . . . 35
52. Scalariform tissue from fern root 35
53. Woody fibre from eider.. «%... « 35
THE MICROSCOPE.
PLATE III. to face page 40.
FIG. PAGE
54. "Glandular" woody tissue 34
55. Transverse section of glandular woody tissue .... 3-1
56. Transverse section of oak 34
57. Long section of oak 34
58. Oblique section of oak 34
59. Section of cork , 35
60. Transverse section of coal 36
61. Longitudinal section of coal 36
62. Wheat starch 37
63. Oat starch 37
64. Potato starch 37
65. Tous-les-mois starch 37
66. Indian corn starch 38
67. Sago starch -. 37
68. Tapioca starch 37
69. Acicular raphides from garden hyacinth 38
70. Bundle of ditto from leaf of aloe contained in a cell 33
71. Compound raphides from stalk of garden rhubarb. . 39
72. Tabular prismatic raphides from outer coat of onion 39
73. Circular crystalline mass from a cactus 39
74. Simple vegetable hair from leaf of a common grass 40
75. Rudimentary hair from flower of pansy 40
76. Simple club-shaped hair, 40
77. Club-shaped hair from leaf of dock 41
78. Hair from throat of pansy 40
79. a. Hair formed of two cells from flower of white
dead-nettle 41
79, 6. Many-jointed tapering hair with nuclei from
common groundsel ..,-., »... 4]
DESCRIPTION OF PLATES. xiii
PTO, PAGE
SO. Beaded hair of sow-thistle 41
81. Glandular hair from leaf of common tobacco 41
82. Hair from leaf of garden chrysanthemum 41
83. Rosette-shaped glandular hair from flower of verbena 41
84. Stellate hairs from the hollyhock (A Ithasa rosea).. 41
85. a. Stellate hair from leaf of lavender 41
85, 6. Hair from leaf of garden verbena, with warty
surface 45
86. Hair from leaf of white poplar (Populus alba) .... 41
87. Ease of a hair on a mass of cellular tissue 41
88, a. A sting from common nettle 42
88, 6. Portion of a leaf of Valisneria 42
PLATE IV. to face page 48.
89. Palmclla cruenta — gory dew 48
90. Yeast plant 48
91. Portions of vinegar plant 48
92. So-called cholera fungus obtained from the air. ... 48
93. Red rust of wheat 49
94. Puccinia yraminis — mildew 49
95. Pent till him glaucum — common mould 49
96. Boirytis from mouldy grape 49
, 97. Fungus from mouldy bread (Mucor Muccdo] .... 49
98. Fungus from human ear 49
99. Fungus from leaf of bramble (Phragmidium bul-
I'osum) 49
100. Vine blight (Oldium Tuckeri) 50
101. Potato blight (Bolrylis infcslans) 50
102. a. Pea. blight (Erysiplie Pisi) 50
6. Asci and sporidia of pea blight CO
103. Fungus from a decayed Spanish nut 50
XIV THE MICROSCOPE,
FIG. PAGE
104. Curious fungus from oil casks 50
105. Fungus of common ringworm (Achorion Schonlenii) 50
106. Fungus on stem of duckweed 50
a. Another within the cells.
107. a. Branched cells from stem of mushroom 51
I. Branched cells from rootlets of mushroom .... 51
C. Reproductive bodies borne ra fours on the gills
of mushrooms 51
108. Section through a brilliant orange-coloured peziza 52
109. Section through the common yellow lichen of trees
and walls 52
110. Leaf of Sphagnum — bog moss 52
111. Sea weed — Polyslphonia fastiyiata 67
a. Fruit-bearing organs.
&. Spore.
c. Portion of Bispore ; and
d. „ Tetraspore.
e. Antheridia.
112. Eeproductive organs of a moss, a species of Tortula 52
a. The calyptra.
6. The operculum.
c. The peristome.
d. The teeth.
e. The spores.
113. Fructification on back of frond of male fern. ..... 53
114. Fructification on back of frond of common brakes 53
115. Capsules of Scolopendrium — hartstongue. The
sporules seen escaping 53
a. One of the latter more magnified 53
116. Fructification of Equisetum — horsetail .......... 55
a. Shield-like disk of ditto, separated, surrounded
by thecffl 55
DESCRIPTION OF PLATES. XV
FIG.
116, 6. Spore, much magnified, with elastic filaments
coiled closely round ...................... 55
c. Spore expanded .......................... 55
117, a. Fructification of Lycopodium — club moss ...... 54
b. Sporules .................... . .... ....... 54
C. Sporules more highly magnified,
PLATE V. to face page 56.
118. Delicate spiral cells from anthers of furze 44
119. Large well-developed spiral cells from anthers of
hyacinth, with minute raphides in intercellular
spaces 44
120. Irregular deposit in cells of anthers of white dead-
nettle 44
121. Annular ducts from anthers of narcissus 44.
122. Stellate cells from anthers of crown imperial .... 44
123. Ovate pollen cells 44
124. Triangular pollen cells from hazel 44
125. Pollen cells of heath 44
126. Pollen cells of dandelion 44
127. Pollen cells of passion flower 45
128. Pollen cells of mallow 45
129. Eed poppy seed 46
130. Black mustard seed 46
131. Seed with deep and curved furrows • 46
132. Great snapdragon seed * 46
133. Chickweed seed 41
134. Umbelliferous seed or fruit •• 46
135. Zygnema, conjugating 60-
136. Clostenum, conjugating • » 57
XV]' THE MICROSCOPE.
FHJ. PAGE
137. Cosmarlum, conjugating .....,,* 57
138. Epiiheiiiia gibbet, conjugating 43
2 39. Melosira nummuloidcs, conjugating 59
110. Transverse section of common sponge 6}
141. Transverse section of common British sponge .... 63
a. Spicules of the same more magnified.
Calcareous spicules of Grantia ciliufa. 68
142. Pin-like spiculum from Cliona, a boring sponge . . 69
143. Spiculum from Spongilla, a fresh-water sponge . . 69
144. Spiculum from unknown sponge 69
145. Spiculum from Tethea f>9
146. Common Hydra 70
a. Stinging organ from common Hydra
147. A species of Sertularia, a zoophyte 71
148. Campanularia Integra, a zoophyte 71
149. " Cup" of Campanularia volubilis, a zoophyte. ... 71
1 50. Spicula of Gorgonia verrucosa 71
151. Transverse section from base of spine of Echinus
neglectus 72
152. Calcareous rosette from sucker of Echinus 72
153. Pedicellaria from Echinus 72
154. Pedicellaria from star-fish 72
PLATE VI. to face page 72.
155. Lepralia, a polyzoon » 72
156. BoicerbanTcia densa, a polyzoon 73
157. Tobacco-pipe, or bird's-head processes of Notamia 73
a. Bird's-heau process.
158. Bugula avicularia 73
159. Bird 's-head process of Bugula Murrayana . «•«» 73
DESCRIPTION OF PLATES. XVU
FIG. PAGE
160. Scrupularia swuposa, with bird's-head processes
(avicularia) and sweeping bristles (vibracula). . 73
161. Snake-headed zoophyte — Anyuinaria 73
162. Flustra foliacea — sea mat 72
163. Plumatdla repens, a fresh-water polyzoon 74
164. Egg of Cristatella Muccdo, a fresh-water polyzoon 74
165. Transverse section of shell of Pinna, showing
prismatic shell structure 74
166. Longitudinal section of shell of Pinna 75
167. Transverse section from oyster-shell 7 ft
168. Section of shell of Anomia, with tubular borings. . 75
169. Section of mother of pearl 75
170. Prawn-shell viewed as a transparent object 75
171. Teeth of whelk 73
172. Teeth of limpet 75
173. Teeth of periwinkle 73
174. Teeth of Limneus 75
175. Scale of sturgeon — ganoid 7^
176. Prickle from back of skate — placoid 7«
177. Borings by a minute parasite in a fossil fish-scale. . ^7
178. Scale of sole — ctenoid »*
179. Scale-, "whiting — cycloid 77
a. CuL-^eous particles, magnified.
180. Scale of sprat — cycloid 7V
181. Section of egg-shell 90
182. From soft egg.
183. Section of egg-shell of emu 90
PLATE VI I. to face page 80.
184. Human hair , . . , 78
a* Transverse section of human hair.
XV111 THE MICROSCOPE.
FIG. PAGE
185, a. Small mouse-hair......,,., , 79
6. Larger mouse-hair.
c. Plain mouse-hair.
d. Minute hair from ear of mouse.
136. Hair of long-eared bat 50
187. Transverse section of hair of peccary 80
183. Pith-like hair of musk-deer SO
1S9. Hair from tiger caterpillar . , So
190. a. Branched hairs from leg of garden spider
(Epeira diadema) 81
b. Spine, with spiral flutings, from the same.
C. Small brush-Lite hairs from an Australian
spider.
191 . Hair from flabellum of crab 81
192. Portion of four of the barbs of a goose-quill 81
193. Portion of the same more magnified 81
194. Swan's-down 81
195. Head and mouth of a flea 82
196. Head and mouth of a bug 82
197. Mandible of humble bee Si
198. Head and mouth of louse §3
199. Head and mouth of gnat . . 83
200. Extremities of barbs of the sting of common bee. . 34
201. Head of honey bee 83
a. Piece of the tongue more magnified.
202. Mouth of blow-fly 84
203. Head and mouth of butterfly 84
204. One of the fangs of a spider, showing the poison-
bag and duct 85
205. Foot of Empis, a species of fly 87
206. Foot of bee 87
207. Foot of spider 87
DESCRIPTION OF TLATES.
FIG.
208. Head of common spider, showing eight simple eyes.
a. Cornea of one of these more magnified 85
209. Skin of garden spider 85
210. Portion of compound eye of fly 83
211. Portions of the two wings of bee in flight 88
a. Nervule of wing.
212. Spiracle of fly 86
213. Spiracle of Dytiscus 86
214. Threads of garden spider (Epeira diadema) 86
Simple thread of the same.
Thread of a concentric circle with viscous dots.
PLATE VIII. to face page 88.
215. Fore leg of Gyrinus natator, whirligig beetle .... 87
216. Middle leg of the same 87
217. Hind leg of same 87
218. Fore leg of male Dytiscus 87
219. Middle leg of the same.
220. a. Gizzard of cockroach 89
6. Ditto, cut open.
221. a. Gizzard of cricket 89
&. Ditto, cut open.
222. Trachea from caterpillar 86
223. Proleg of caterpillar of common garden white
butterfly, with the membranes in which the
hooks are seated, expanded as in action 83
224. Part of leg of cockroach
225. Battledore scale from blue argus butterfly 88
226. Scale of ordinary shape from same 88
227. Scale from meadow-brown butterfly 88
228. Scaleofgnat .33
XX THE MICROSCOPE.
PIG. PAGE
229. Scale reduced to a hair from clothes-moth 85
230. Hair-like scale from clothes-moth, with three
prongs 89
231. Cartilage from mouse's ear 91
232. Transverse section of human bone 90
233. Striped muscular fibre from meat 92
234. a. Liber fibre of flay, natural state , . . . . 79
b. Ditto, broken across at short intervals
235. Wool from flannel 79
236. Silk ., 79
237. Cotton hair 79
238. Crystal of honey f;l>
239. Thick crystal of ordinary sugar — same angles .... 39
240. Crystals of sugar from adulterated honey 40
241. Cuticle from berry of holly 35
242. Transverse section of whalebone 90
243. Transverse section of plum-stone 31
244. Transverse section of testa of seed of Guelder rose 13
245. Fruit of groundsel — opaque 42
246. One hair of pappus of dandelion 42
247. Cottony hair of burdock 42
248. Portion of pappus of goats-beard 42
249. "Wood of young shoots of vine, the cells containing
starch S3
250. Spiral fibres from testa of wild sage seed 35
PLATE IX. Frontispiece to face title-page.
1. lodo-sulphate of Quinine
2. Salicine
3. Aspartic Acid
4. Sulphate of Copper in Gelatine
5. Grey Hair (human)
6. Scales of Hyppophas rhainnoides
VrWestimp.
Robert Eandwicke ,1860
HALF-HOURS WITH THE MICROSCOPE,
CHAPTER I .
A HALF-HOUE ON THE STEUCTUEE OF THE
MICEOSCOPE.
THE Microscope is often regarded merely as a
toy, capable of affording only a certain amount of
amusement. However much this might have been
the case when its manufacture was less perfectly
understood, it is now an instrument of so much
importance that scarcely any other can vie with
it in the interest we attach to the discoveries made
by its aid. By its means man increases the power
of his vision, so that he thus gains a greater know-
ledge of the nature of all objects by which he is
surrounded. What eyes would be to the man who
is born blind, the Microscope is to the man who
sees only with his naked eye. It opens a new
world to him, and thousands of objects whose form
and shape, and even existence, he could only ima-
gine, can now be observed with accuracy.
Nor is this increase of knowledge without great
advantages. Take for instance the study of plants
and animals. Both are endowed with what we
call life : they grow and perform certain living
functions ; but as to the mode of their growth, and
the way in which their functions were performed,
little or nothing was known till the Microscope
revealed their minute structure, and showed fe^\N v
thei*- Carious parts were related to each other. The
B
2 THE STRUCTURE OF
Microscope has thus become a necessary instrument
in the hands of the botanist, the physiologist, the
zoologist, the anatomist, and the geologist.
Let us. then, endeavour to understand how it is
this little instrument has been of such great service
in helping on the advancement of science. Its use
depends entirely on its assisting the human eye to
see — to see more with its aid than it could possibly
do without it. This it does by enabling the eye to
be brought more closely in contact with an object
than it otherwise could be.
Just in proportion as we bring our eyes close to
objects, do we see more of them. Thus, if we look
at a printed bill from the opposite side of a street,
we can see the larger letters only ; but if we go
nearer we see the smaller letters, till at last we get
to a point when we can see no more by getting
closer. Now suppose there were letters printed on
the bill so small that we could not see them with
the naked eye, yet, by the aid of a lens — a piece of
convex glass — we could bring our eyes nearer to
the letters, and see them distinctly. It would depend
entirely on the form of the lens, as to how close we
could bring our eyes to the print, and see; but this
great fact will be observed, that the nearer we can
get our eyes to the print, the more we shall see.
The most important part of a Microscope, then,
consists of a lens, by means of which the eye can
be brought nearer to any object, and is thus enabled
to see more of it. Magnifying-glasses and Simple
Microscopes consist mainly of this one element.
In order, however, to enable the eye to get as close
as possible to an object, it becomes convenient to
use more than one lens in a glass through which we
look. These lenses, for the sake of convenience,
are fixed in a brass frame, and attached to the
Simple Microscope ; when there are two lenses they
THE MICROSCOPE. 3
are called doublets, and when three they are termed
triplets. The magnify ing-glasses which are made
to be held in the hand, frequently have two or
three lenses, by which their power may be increased
or decreased. Such instruments as these were the
first which were employed by microscopic observers:
and it is a proof of the essential nature of this
part of the Microscope, that many of the greatest
discoveries have been made with the Simple Mi-
croscope.
The nearer the glass or lens is brought to an
object, so as to enable the eye to &ee, the more of
its details will be observed. So that when we use
a glass which enables us to see within one inch of
an object, we see much more than if we could bring
it within only an inch and a half or two inches.
So on, till we come to distances so small as the
eighth, sixteenth, or even twentieth of an inch.
Although a great deal may be seen by a common
hand-glass, such as may be purchased at an optician's
for a few shillings, yet the hand is unsteady ; and
if these glasses were made with a very short focus,
it would be almost impossible to use them. Besides,
it is very desirable, in examining objects, to have
both hands free. On these accounts the glasses,
which in such an arrangement are called object-
glasses (see fig. 3), are attached to a stand, and placed
in an arm, which moves up and down with rack-
work. Tn this way, the distance of the object from
the glass can be regulated with great nicety. Under-
neath the glass, and attached to the same stand, is
a little plate or framework, to hold objects, which
are placed on a slide of glass. This is called the
stage. (Fig. 1, G.) Sometimes rack-work is added to
this stage, by which the objects can be moved upon
it backwards and forwards, without being moved
by the hand. Such an arrangement as this is
B 2
4: THE STRUCTURE OF
called a Simple Microscope. Of course many other
things maybe added to it, to make it more conveni-
ent for observation ; but these are its essential parts.
But, although the Simple Microscope embraces
the essential conditions of all Microscopes, and has,
in the hands of competent observers, done so much
for science, it is, nevertheless, going out of fashion,
and giving way to the Compound Microscope. (Fig. 1,
p. 5.) This instrument, as might be inferred from its
name, is much more complicated than the Simple
Microscope, but it is now constructed with so much
accuracy, that it can be used with as great cer-
tainty and ease as the Simple Microscope itself. In
order to understand the mechanism of the Compound
Microscope we must first of all study the principles
on which it is constructed. If we take a common
convex lens and place any small object on one side
of it, so as to be in its focus, and then place on the
other side a sheet of white paper, we shall find at
a certain point that an enlarged picture of the
object will be produced on the paper ; and this is
the way in which pictures are formed by the
camera of which the photographic artist avails
himself for his portraits and sun-pictures. Now L
we look at this picture with another lens of the
same character but of somewhat less magnifying
power, we shall obtain a second picture larger than
the first, and this is the principle involved in the
Compound Microscope. The superiority of this
instrument over the Simple Microscope consists in
an increase of magnifying power. There is, how-
ever, a limit to the utility of this magnifying power ;
for when objects are greatly magnified they become
indistinct. This is seen in the Oxyhydrogen and
Solar Microscopes, where the images are thrown, by
means of highly magnifying lenses, on a white sheet;
and, although made enormously large, their details
THE MICROSCOPE. 5
are much less clear than when looked at by a lens
magnifying much less. Another advantage of the
Fig. 1 *
Compound Microscope.
Compound Microscope is the distance at which the
eye is placed from the object, and the facility with
* In this little work we have purposely abstained from
mentioning either the names or the Microscopes of our
principal makers, lest we should thereby seem to give a
6 THE STRUCTURE OF
wLich the hands may be used for all purposes of
manipulation.
A brief description, aided by the accompanying
illustration, will, it is hoped, suffice to make the
beginner acquainted with the various parts of this
important instrument.
We have already mentioned that when powerful
lenses are used in the examination of small objects
the hand is not sufficiently steady to give a firm
support to the lens employed, and this is equally
true of the hand that holds the object. It is also
essentially requisite to have both hands free, for
the purpose of manipulation. Hence it becomes
necessary to devise some mechanical means for the
support of both the lens and the object. How
these wants have been supplied by the enterprising
skill and ingenuity of our opticians will be best
seen as we describe the various parts of which the
Compound Microscope consists.
The most important part of the instrument is
undoubtedly that which carries the various lenses
or magnifying powers. These are contained in the
interior of the tube or body, A, which is usually
constructed of brass, and from 8 to 10 inches in
length. At the upper end of the tube is the eye-
piece, B, so named from its proximity to the eye of
the observer. It consists of two plano-convex
lenses, set in a short piece of tubing, with their
flat surfaces turned towards the eye, and at a
distance from each other of half their united focal
lengths. The first of these lenses is the eye-glass,
while that nearest the objective is termed the field
lens. The use of the latter is to alter the course
preference to any. The general excellence of these instru-
ments is so well known and the names of their makers are
so universal that the student will find no difficulty in provid-
ing himself with an efficient instrument at a moderate cost.
THE MICROSCOPE.
of the light's rays in their passage to the eye, in
such manner as to bring the image formed by the
object-glass into a condition to be seen by the eye-
glass. A stop also is placed between the two lenses
in such a position that all the outer rays, which pro-
duce the greatest amount of distortion, arising from
spherical and chromatic aberration, are cut off. The
short tube carrying the lenses (fig. 2) slides freely,
but without looseness, into the upper end of the com-
pound body, A, an arrangement which affords a ready
and convenient method for changing the eye-pieoe.
Compound Microscopes
are generally fitted up
with two eye-pieces, the
one deep and the other
shallow. The last has its
lenses close together, and
magnifies the most, whilst
the other has them far-
ther apart, and magnifies
less. In the use of these
eye-pieces, it should never
be forgotten that the one
which magnifies least is
generally the most trust-
worthy.
Fig. 2. Eye-piece.
At the opposite end of the tube A is the object-
glass C. The use of this lens is to collect and
bring to a point the rays of light that proceed
from any object placed in its focus. At this point
an enlarged image of the object will be formed in
the focus of the eye-glass. We have only to look
through the latter at the picture thus formed in
order to obtain a second image larger than the
first. And this is the way in which minute objects
are made to appear so much larger than when seen
by the unassisted eye. It will at once be seen how
8 THE STRUCTURE OP
much of the utility of a Microscope depends on
good object-glasses. Where they are faulty, the
image they form is also faulty ; and when these
faults in the first image are multiplied by the
power of the eye-piece, they become — like the faults
of our friends when viewed through a similar
medium — of great magnitude.
A good object-glass may be known by its giving
a clear and well-defined view of any object we may
wish to examine ; while a bad lens may be equally
well known by the absence of these qualities. In
short, a badly constructed objective is more apt to
mislead than to guide the student, by the fictitious
appearances it creates — appearances that may be
erroneously taken for realities, which have no exist-
ence in the object itself. The object-glasses of our
best opticians consist of several
lenses arranged in pairs, set in a
small brass tube. A screw at
one end serves to attach them
to the lower extremity of the
compound body, A. (Fig. 3.)
The body of the Microscope is
supported by a stout metal arm,
D, into the free end of which it
screws. The opposite end of the
arm is secured to the stem, E,
by a screw, on which it moves
Fig. 3. Object-Glass. af on a Pivot« B7 this means
the tube of the Microscope can
be turned away from the stage — an arrangement
that gives this form of Microscope an advantage
over those that are not so constructed. To the
stem, J£, which works up and down a hollow pillar
by rack-work and pinion, is attached the stage, G.
This, in its simplest form, consists of a thin flat
plate of brass, for holding objects undergoing ex-
THE MICROSCOPE. 9
animation. In the centre is a circular opening, for
the passage of the light reflected upward by the
mirror, H. There is also a sliding ledge, // against
this the glass slide, on which the object is mounted,
rests, when the Microscope is inclined from the
perpendicular.
In a stage of this kind the various parts of an
object can only be brought under the eye by
shifting the slide with the fingers. But in more
expensive instruments the stage is usually con-
structed of one or two sliding plates, to which
motion is given by rackwork and pinion ; the
whole being brought under the hand of the operator
by two milled heads, a mechanical arrangement
which enables him to move with ease and certainty
the object he may wish to investigate.
Underneath the stage
is the diaphragm, K, a
contrivance for limiting
the amount of light
supplied by the mirror,
H. It consists of a
thin, circular, flat plate
of metal, turning on a
pivot, and perforated
with three or four cir-
cular holes of varying
diameter (fig. ^ 4), the Diaphragm.
largest only being equal
to the aperture in the stage. By turning the plate
round, a succession of smaller openings is brought
into the centre of the stage, and in one position of
the diaphragm the light is totally excluded. By
this small but useful contrivance the Microscopist
can adjust the illumination of the mirror to suit
the character of the object he may be investiga-
ting. In some Microscopes the diaphragm is a fix-
10 THE STRUCTURE OF
ture, but in the better class of instruments it is
simply attached to
the under part of
the stage by a bayo-
net catch, or by a
sliding plate of me-
tal (fig. 5), and can
be readily removed pig. 5. Diaphragm,
therefrom when it
is desirable to employ other methods of illumi-
nation.
In working with the Microscope it is necessary
to adopt some- artificial means for ensuring a larger
supply of light than can be obtained from the
natural diffused light of day, or from a lamp or
candle. For this purpose the Microscope is fur-
nished with a double mirror, H, having two reflect-
ing surfaces, the one plane and the other convex.
The latter is the one usually employed in the illu-
mination of transparent objects ; the rays of light
which are reflected from its concave surface are
made to converge, and thus pass through the object
in a condensed form to the eye. The plane mirror
is used generally in conjunction with an achromatic
condenser, when parallel rays only are required.
The whole apparatus is attached to that portion of
the hollow pillar continued beneath the stage, in
such a manner that it can be moved freely up and
down the stem that supports it. This motion
enables the Microscopist to regulate the intensity
of his light by increasing or decreasing the distance
between the mirror and the stage ; while the
peculiar way in which the mirror itself is suspended
on two points of a crescent-shaped arm, turning on
a pivot, gives an almost universal motion to the
reflecting surfaces. The observer by this means
can secure any degree of oblique illumination ha
THE MICROSCOPE. 11
may require for the elucidation of the structure
undergoing examination.
We next come to the stand, which, though the
most mechanical, is at the same time a very impor-
tant part of the Compound Microscope. On the
solidity and steadiness of this portion of the instru-
ment depends in a great measure its utility. The
form generally adhered to is that represented in our
diagram (fig. 1, p. 5.) It consists of a tripod base, P,
from which rise two flat upright pillars, 0. Between
these, on the two hinge-joints shown at L, is sus-
pended the whole of the apparatus already described :
namely, the body carrying the lenses, the arm to
which it is attached, the stage, and the mirror
underneath it. By this contrivance the Microscope
can be inclined at any angle between a vertical and
horizontal position — an advantage which can be duly
appreciated by those who work with the instrument
for two or three hours at a time. Close to the
points of suspension are the milled heads, M ; these
are connected with a pinion working in a rack cut
in the stem, E. By turning the milled heads the
tube is made to approach or recede from the stage
until the proper focus of the object-glass is found.
This is termed the coarse adjustment, and is gene-
rally used for low powers, where delicate focussing is
not required. But when high magnifying powers
are used, that require a far greater degree of pre-
cision, we have recourse to the fine adjustment, N,
which consists of a screw acting on the end of a
lever. The head of the screw by which motion ic
communicated to the object-glass is divided into ten
equal parts, and when caused to rotate through any
of its divisions slightly raises or depresses the tube,
carrying the objective with it. As the screw itself
contains just 150 threads to an inch one revolution
of its head will cause an alteration of the 150th
12 THE STRUCTURE OF
of an inch in the distance of the lens from the
object. When moved through only one of its
divisions we obtain a result equal to the 1500th of
an inch, and by causing it to rotate through half a
division we secure a movement not exceeding the
3000th part of an inch in extent. Such nicety in
the adjustment of the optical part of the Micro-
scope may seem to the beginner unnecessary, but
when he comes to work with high powers he will
find that he needs the most delicate mechanical
contrivances to enable him to secure the proper
focus of a sensitive object-glass.
But this is not the only use to which we can put the
fine adjustment. The same process that serves to re-
gulate the focus of a lens will also enable us to measure
pretty accurately the thickness of an object or any
of the small prominences or depressions found in its
structure. By observing the number of divisions
through which the head of the screw is made to
pass while changing the focus of the object-glass
from the bottom to the top of any small cavity or
prominence we get a tolerable notion of its depth
or height, &c. Connected with this apparatus is a
special contrivance for protecting the object-glass
to some extent from injury. It will sometimes
happen, even with the most careful, when using
high powers, that the lens is brought down with
some force in contact with the glass cover that
protects the object. This risk is not unfrequently
incurred by admitting to one's study incautious
friends, whose confidence is only equalled by their
ignorance ; who although they may have never seen a
Microscope before, will proceed to turn it up and
down with a force sufficient to crack the lens.
Such friends would have sufficient confidence in
themselves to take the command of a man-of-war,
even though it were the first time in their lives
THE MICROSCOPE, 13
they Lad been on board a ship. Strict injunctions
must be laid on all such not to approach the table
until the instrument is quite ready for them to take
a peep, coupled with a polite request that while
doing so they will keep their hands behind them.
A provision has been made which to some extent
provides for such an emergency. The object-glass
itself is screwed into a short tube, that fits accu-
rately the lower end of the compound body and
slides freely within it, being kept down in its place
by a spiral spring, which presses upon it from
behind. On the application . of a slight force or
resistance to the object-glass the spring tube
immediately yields, within certain limits, to the
pressure, carrying with it the lens, which is thus
often saved from destruction. Object-glasses of
various degrees of magnifying power and excellence
of workmanship are supplied with th-e Microscope,
and may be purchased separately, according to the
wants and resources of the student. It will be
found that for all ordinary purposes the 1-inch and
1-inch objectives are the most useful powers. A
substitute for the intermediate powers may be
obtained by pulling out the draw-tube and using
the higher eye-pieces. This method, though not so
satisfactory in its results as the use of separate
object-glasses, may be resorted to where a series
of objectives are not within the reach of the
observer.
THE BINOCULAR MICROSCOPE.
Since the invention of the Stereoscope attempts
have been made to apply the Binocular principle
in the construction of the Compound Micro-
scope. After some failures this desideratum has
been successfully achieved by Mr. F. H. "Wenham,
a gentleman well known to microscopists by
14: THE STRUCTURE O¥
the fertility of his resources and the ingenuity of
his inventions in connection with the Microscope.
It is to him that we are indebted for a Microscope
that enables us to see objects in a natural manner,
namely, with both eyes at once. Hitherto the
ordinary single-tubed Microscope reduced the ob-
server to the condition of a Cyclops. Although
gifted with a pair of eyes he found it impossible to
avail himself of this plurality of organs. He was
condemned by the very nature of his Microscope
to peer perpetually with a single eye through its
solitary tube ; but thanks to- Mr. Wenham all this
is changed. We have now the satisfaction of using
a double-tubed Microscope that not only gives em-
ployment to both eyes at once, but presents us with
effects unknown and unattainable by the ordinary
instrument. We no longer gaze at a flat surface,
but a stereoscopic image stands out before us with
a boldness and solidity perfectly marvellous to those
who have only been accustomed to the ordinary
single-tubed Microscope.
" No one," says a writer in ' The Popular Science
He view,' " can fail to be struck with the beautiful
appearance of objects viewed under the Binocular
Microscope. Its chief application is to such objects
as require low powers, and can be seen by reflected
light, when the wonderful relief and solidity of the
bodies under observation astonish and delight even
the adept. Foraminifera, always beautiful, have
their beauties increased tenfold ; vegetable struc-
tures, pollen, and a thousand other things, are seen
in their true lights, and even diatoms, we may pre-
dict, will receive elucidation, as to the vexed ques-
tions of the convexity or concavity of their infinitely
minute markings. The importance of the Binocular
principle is especially apparent when applied to
anatomical investigation. Prepared Microscopic
TIIE MICROSCOPE.
injections exhibit under the ordinary Microscope a
mass of interlacing vessels, whose relation, being
all on the same plane, it is not easy to make out
with any degree of satisfaction. But placed under
the Binocular they at once assume their relative
position. Instead of a flat band of vessels, we now
see layer above layer of tissue ; deeper vessels an-
astomosing with those more superficial ; the larger
vessels sending branches, some forward and some
backward, and the whole injection assumes its
natural appearance, instead of being only like a
picture"
Fortunately for the possessors of the ordinary
Microscope, the Bin-
ocular arrangement
can be readily adapted
to this instrument at
a cost of a few-
pounds. The addi-
tional tube and prism
does not interfere
with the use of the
instrument as a mon-
ocular, the withdrawal
of the prism instantly
converts it into that
form of instrument :
this is necessary when
high powers are
used.
The accompanying
diagram (fig. 6) — a
section of the Bin-
ocular — will give *
the reader a correct Fig. 6. Section of
notion of the mecha- Binocular Microscope.
16 THE STRUCTUKE OF
nism of the instrument. Let G represent the body
of the ordinary Microscope and £ the secondary
tube attached to the side of the former, which it
will be seen has a portion of its surface cut away
at the point of junction, F, as a means of commu-
nication between them. The eye-pieces and draw-
tubes are seen at D and E. The object-glass G
is attached to the ordinary tube C in the usual
way. Just above it is the small prism, A,
mounted in a brass box, and so constructed as
to slide into an opening in the tube at the back
of the object-glass. By this arrangement it will
be found that while one half of the light passes up the
tube unobstructed the other half must first pass
through the prism, where,
after undergoing two re-
flections (fig. 7), it es-
capes in the direction of
the additional tube B. The
dotted lines in the diagram
show the direction the
light takes in its passage
to the eyes. At H the rays
are seen to cross each other.
Those from the left side of
the obj ect-glass traverse the
. _ right tube, while those from
Double-reflecting Prism. ^ rigbt'side of the lens
are projected up the left tube.
In using the Binocular it must be remembered
that the eyes of different individuals vary in their
distance from each other. It will thus be seen
that some contrivance is necessary to enable us to
increase or decrease the distance between the eye-
pieces to suit the requirements of all. This is
accomplished by the two draw-tubes, D and E,
which carry the eye-pieces. When drawn out, the
THE MICROSCOPE. IT
latter are made to diverge, and when pushed iu
they converge. In this way any intermediate
distance can be obtained to suit every kind of
vision.
"Where a Binocular Microscope is in daily use it
will sometimes be necessary to withdraw the prism
from the tube, to cleanse it from dust and other
impurities gradually contracted by use. Whenever
this may be necessary great care should be taken
to employ no substance likely to scratch its highly
polished surfaces; for on these being preserved intact
in a great measure depends the efficiency of the in-
strument. We know of nothing better adapted for
removing impurities than a clean silk or cambric
handkerchief, which, when not in use, should be kept
in a closely-fitting drawer, to protect it from dust.
There seems to be little doubt that this lately
improved form of the Compound Microscope will
eventually supersede all others. This opinion also
seems to be entertained by the inventor himself,
whose words we quote : —
" The numerous Microscopes that have been
altered into Binoculars, in accordance with my last
principle, and also the large quantity still in the
course of manufacture, will, I think, justify me in
making the assertion, without presumption, that
henceforth no first-class Microscope will be con-
sidered complete unless adapted with the Binocular
arrangement."
The Compound Microscope is now, undoubtedly,
one of the most perfect instruments invented and
used by man. In the case of all other instruments,
the materials with which they are made and the
defects of construction are drawbacks on their per-
fect working ; but in the Compound Microscope
we have an instrument working up to the theory
of its construction. It does actually all that could
c
18 THE STRUCTURE OF
be expected from it, upon a correct theory of the
principles upon which it is constructed. Neverthe-
less, this instrument did not come perfect from its
inventor's hands. Its principles were understood by
the earlier microscopic observers in the seventeenth
and eighteenth centuries, but there were certain
drawbacks to its use, which were not overcome till
the commencement of the second quarter of the
present century.
These drawbacks depended on the nature of the
lenses used in its construction. The technical term
for the defects alluded to are chromatic and spheri-
cal aberration. Most persons are acquainted with
the fact that, when light passes through irregular
pieces of cut glass — as the drops of a chandelier, —
a variety of colours is produced. These colours,
when formed by a prism, produce a coloured image
called the spectrum. Now, all pieces of glass
with irregular surfaces produce, more or less, the
colours of the spectrum when light passes through
them j and this is the case with the lenses which
are used as object-glasses for Microscopes. In
glasses of defective construction, every object
looked at through them is coloured by the agency
of this property. The greater the number of
lenses used in a Microscope, the greater, of course,
is the liability to this colouring. This is chromatic
aberration ; and the liability to it in the earlier-
made Compound Microscopes was so great that it
destroyed the value of the instrument for purposes
of observation.
Again, the rays of light, when passing through
convex lenses, do not fall — when they form a
picture — all on the same plane; and therefore,
instead of forming the object as presented, pro-
duce a picture of it that is bent and more or less
distorted. This is spherical aberration, and a fault
THE MICROSCOPE. 19
which was liable to be increased by the number of
glasses, in the same way as chromatic aberration.
This defect also is increased in Compound Micro-
scopes ; and formerly, the two things operated so
greatly to the prejudice of this instrument that it
was seldom or never used.
Gradually, however, means of improvement were
discovered. These defects were rectified in tele-
scopes; and at last a solution of all the difficulties
that beset the path of the Microscope-maker was
afforded by the discoveries of Mr. Joseph Jackson
Lister, a gentleman engaged in business in London,
who, in a paper published in the Philosophical
Transactions for 1829, pointed out the way in
which the Compound Microscope could be con-
structed free from chromatic and spherical aberra-
tion. This is done by such an arrangement of the
lenses in the object-glass, that one lens corrects the
defects of the other. Thus, in object-glasses of the
highest power, as many as eight distinct lenses are
combined. We have, first, a triplet, composed of
two plano-convex lenses of crown-glass, with a
plano-concave of flint-glass between them. Above
this is placed a doublet, consisting of a double
convex lens of crown, and a double concave one of
flint-glass. At the back of this is a triplet, which
consists of two double convex lenses of crown-
glass, and a double concave one of flint placed be-
tween them. Such are the combinations necessary
to correct the defects of lenses when employed in
Compound Microscopes.
It is this instrument, then, which is most com-
monly employed at the present day, and to which
we are indebted for most of the recent progress in
microscopic observation.
In using the Microscope, a great variety of acces-
sory apparatus may be employed to facilitate the
c 2
20
THE STRUCTURE OF
various objects which the observer has in vievr.
As this is a book for beginners, w<; shall only
mention a few of these.
Microscopes are generally supplied with small
slips of glass, three inches long and one inch wide.
These are intended to place the objects on which
are to be examined. They are cither used tempo-
rarily or permanently with this object in view,
Fig. 8. Forceps.
and are called slides. When used temporarily, an
object, such as a small insect, or part of an insect,
Fig. 9. Bull's-eye Condenser.
is placed upon the middle of it ; and it may be
either placed immediately upon the stage at the
THE MICROSCOPE, 21
proper distance from the object-glass, or a drop
of water may be placed on the slide, and a piece
of thinner glass placed over the object. This is
the most convenient arrangement, as you may
then tilt your Microscope without the slide or
object falling off.
Objects, when placed under the Microscope, are
of t\vo kinds — either transparent or opaque. When
they are opaque, they may either be placed upon
the slips of glass, or put between a small pair of
forceps (tig. 8), which are fixed to the stage of the
Microscope, and the light of a window or lamp
allowed to fall upon them. This is not, however,
sufficient, generally, to examine things with great
accuracy ; and an instrument called a condenser
(tig. 9) is provided for this purpose. It consists
merely of a large lens, which is sometimes fixed to
the stage, or has a separate stand. Its object is to
allow a concentrated ray of light to be thrown on
the opaque object whilst under the object-glass of
the Microscope. This is called viewing objects by
reflected light.
Transparent objects, *>n the other hand, are
viewed by transmitted light, reflected from the
plane or concave surface of the mirror beneath the
stage. The object of this mirror, which is called
the re/lector, is to caU«h the rays of light and con-
centrate them on the object under the Microscope^
The rays of light thus pass through the object, and
its parts are sesii much more clearly.
Another convenient piece of apparatus is an
animalcule cage. This consists of a little brass box,
inverted, to the bottom of which is attached a
piece of glass. Over this, again, is placed a lid
or cover, with a glass top. The cover can be made
to press on the glass beneath, and an object being
placed between the two glasses, can be submitted
22 THE STRUCTURE OF
to any amount of pressure thought necessary,
(Fig. 10.) This is a very important instrument
for examining minute Crustacea, animalcules,
zoophytes, and other living and moving objects,
especially when they live in water.
Fig. 10. Animalcule Cage or Live Box.
In the use of the cage and the slide, care must
be taken not to break them by turning the object-
glass down upon them. It is sometimes a difficult
thing, when the object-glass has a focus of not
more than a quarter or eighth of an inch, to adjust
it to exactly the point at which the object is best
seen, by means of the coarse handles on the rack-
work. For this reason the Microscope has been
provided with a fine adjustment, by which the
object-glass is moved down on the object in a
much slower and more gradual manner, and the
destruction of an expensive objective glass is often
thus prevented.
The picture of the object brought to the eye in
the Compound Microscope is always the wrong end
upwards. That is, the picture is always the reverse
in the Microscope to what it is with the naked eye.
You need constantly to be aware of this, especially
if you are going to dissect an object under the
Microscope, as your right hand becomes left, and
your left right. The observer, however, soon gets
accustomed to this, and it creates no difficulty ulti-
mately. But science constantly attends on the
THE MICROSCOPE.
23
Microscope, and ministers to its slightest defects.
A little instrument called an erector, composed of
a lens which reverses the picture once more, is
supplied by the optician, and can be had by
those who practise the refinements of microscopic
observation.
It is a good plan to make drawings of all objects
examined, or at any rate those which are new to
the observer. A note-book should be kept for this
purpose, and what cannot at once be identified by
the object, may afterwards be so by the drawing.
All persons, however, have not the gift of drawing,
and for those who need assistance in this way, the
camera lucida has been invented. This instrument
is applied to the tube of the Microscope when placed
at right angles with
the stem, in such a
way that a person
looking into it sees
the object directly
under his eye, so that
he may easily draw
its form on a piece
of paper placed un-
derneath. (Fig. 11.)
Some little practice
is, however, necessary
before the observer
can obtain satisfac-
tory results with this
instrument. It is
absolutely essential
that the eye should
be so placed that,
while one part of the
Fig. II. Camera Lucida.
pupil receives the rays from the reflecting surface
24 THE C'i'AUCTURE OF
of the prism, the other sees the paper below with
the image clearly depicted upon it. Dr. Beale
strongly recommends the neutral lens glass
reflector in preference to the Wollaston camera
lucida. It is also much less costly. (Fig. HA.)
This consists of a short tube falling
upon the eye-piece, with a piece of
neutral lens glass placed at such an
angle that, whilst the image of the
object is reflected upwards, the paper
below can be distinctly seen. (The
price of this form of camera lucida is
about four or five shillings.) Success
in the use of the camera depends very
Fig. HA. much on the arrangement of the light.
If the image is too strongly illuminated,
the paper will hardly be visible ; and, on the
contrary, if the paper and pencil are too bright,
the image is indistinct. A little practice will
enable the observer to overcome both difficulties :
this he will have attained when he can see the
image and paper with equal distinctness.
Another instrument which will be found of con-
siderable service even to the beginner with the
Microscope, is a micrometer' This is an instrument
for measuring the size of objects observed. Exag-
gerated notions about the smallness of objects arc
very prevalent j and as it is almost impossible to
say accurately how small an object is without some
means of measuring, a Micrometer becomes essen-
tial where accuracy is desired. This is effected by
having some object of known size to compare with
the object observed. The most convenient instru-
ment of this kind is a glass slide, on which lines
are drawn the hundredth and thousandth of an
inch apart. If this slide, or stage micrometer as it
is called, is placed on the stage,, the divisions may
THE MICROSCOPE. Z.O
be traced on the paper in the same way as the
outline of an object : the dimensions of the latter can
now be ascertained. Care must, however, be taken
that the magnifying power is the same in both cases.
Amongst the accessory apparatus are various
arrangements for concentrating the light en the
objects which are placed for examination under
the Microscope. One of these combinations is
called the achromatic condenser. This consists of
a series of lenses, which are placed between the
mirror and the stage, and which may consist of
an ordinary object-glass. The stages of the larger
kinds of Microscopes are fitted up with a screw or
slide, by which the condenser can be fastened
beneath and adjusted to the proper focus for
throwing light on the object examined.
The illumination of opaque objects by means of
the bull's-eye condenser is sufficient when only the
lowest powers are used ; but when any objective of
less than inch-and-half focus is used this method of
illumination is not satisfactory, and a form of
reflector called a Lieberkiihn will be found to be a
welcome addition to the Microscope. This instru-
ment consists of a concave silvered speculum with
a central aperture of the diameter of the front lens
of the objective : a short tube is attached to the
convex surface of the reflector, which slides over
the object-glass. The action of the Lieberkiihn will
be easily understood from the following diagram :
a represents the objective with the LielerJcilhn in
situ ; 6, the concave reflector j c, a stop for the
purpose of preventing any direct light entering the
objective (a small disk of black paper attached to
the slide is generally sufficient) ; d, d, rays of light
from the mirror ; e, e, reflected rays converging to
a focus at f (the object). To obtain the full
effect of this mode of illumination the mirror should
THE STRUCTURE OF
be placed a little out of the axis of the tube of the
Microscope. By this method an oblique beam of
light is thrown on the Lieberkuhn, and the light
from it is reflected unequally upon the object ; thus
producing the light and shade so necessary for the
proper definition of an object. (The cost of a
Lieberkuhn varies from 6s. to 15s. ; those for low
powers costing more than those for the higher.)
The details of many
transparent objects
are much more dis-
tinctly seen when
examined by light
transmitted by the
object only. This is
called black ground
illumination, and can
be obtained in several
ways. With a very
low power the light
can be reflected with
sufficient obliquity if
the mirror is thrown
out of the axis ; but
much better effects
Fig. llB. Diagram illustrating are obtained when a
the action of a «• Lieberkiihn." hemispherical lens
a, omect-glasg ; o. a concave -.i 1111
silver 'reflector ; c, a black spot Wlth a cenlral black
("dark well") ; d, d, rays of light; stop, called a " spot
e, e, the same reflected and lens," is placed be-
brought to a focus at/. neath the object. The
accompanying figure will explain its action : —
a is " spot lens " ; b, a brass tube in which
it is mounted (this is fitted into a larger tube
fitted to the short tube attached to the lower
surface of the stage : by sliding this up or down, the
proper distance from the object is obtained) ; c,
THE MICROSCOPE.
parallel lines from mirror ; d, the same rays made
to rapidly converge by passing through the lens,
and come to a focus at e j and if the focal length
of the objective is greater than the distance between
the object and the point e, the object will be illu-
minated, and the field appear perfectly dark.
Kg. lie.
a, " Spot Lens," front view ; c, blackened concavity of
ditto ; a', section of " Spot Lens " in its fitting, b ; c', central
stop ; d d, parallel rays of light converging to a focus at e.
Having said thus much with regard to apparatus,
we will now give some directions for the use of
the Microscope under ordinary circumstances. The
Microscope may be either used by the light of the
sun in the daytime, or at night by some form of
artificial light. It is best used by daylight, as
artificial light is likely to tire the eyes.
Having determined to work by daylight, some
spot should be selected near a window, out of the
28
THE STKUCTCRE OF
direct light of the sun, in which to place a small,
firm, steady table. On this the Microscope should
be placed, and the object-
1 glass should be screwed on
to the tube. The mirror
should be then adjusted so
as to throw a bright ray of
light on to the object-glass.
The eye-piece having been
previously placed at the top
of the tube, the Microscope
is now ready to receive a
transparent object. If the
object to be examined is an
animalcule, it may be con-
veyed to the animalcule-cage
by means of a glass tube,
called a pipette or dipping-
tube (fig. 12), which should
be dipped into the water
where the object is con-
tained, with the finger
covered over the upper orifice,
so that no air can escape.
By taking the finger off
when the tube is in the
water, the fluid will rush
into the tube, and with it
the object to be examined.
The finger is again applied
Fig. 12. Dipping Tubes, to the top of the tube, an 1
the fluid obtained conveyed
to the animalcule-cage. Only such a quantity of
the water should be allowed to fall out of the
tube on to the cage as will enable the observer
to put on the cover of the cage without pressing
THE MICROSCOPE. 29
the fluid out at the sides of the cage. If the
water is thus allowed to overflow, it runs over
the glasses of the cage, and thus obscures vision.
An object or objects having been thus placed
in the cage, it is conveyed to the stage, and
placed in such a position that the ray of light
passing from the mirror to the object-glass may
pass through it. This having been done, the
observer must now place his eye over the eye-piece,
and use the screw in the tube, and move the object-
glass downwards until he gets a clear view, of objects
moving in the water. This is called focussing.
The glass may then be moved up or down, in
order that the best view of the object may be
obtained. When the object-glass is one of high
power, the fine adjustment may be used for this
purpose. When the proper focus is obtained, the
object may be moved up or down, right or left,
with the hand, or by the aid of the screws which
are employed in the various forms of what are called
mechanical stages.
When objects not requiring the live-box or
animalcule - cage are to observed, they may be
transferred to the glass slide by aid of a thin slip
of wood, or a porcupine-quill moistened at the end,
or by a pair of small forceps. (Fig. 8.) Some
transparent objects may be seen without any me-
dium, but generally it, is best to place them 011 the
slide with a drop or two of clean water, which may
be placed on it with a dipping-tube. When water
is used, it will generally be found best to cover the
object with a small piece of thin glass. Small
square pieces of thin glass are sold at all the
opticians' shops for this purpose. The object is
then placed under the object-glass as before.
In order to render objects transparent, so that
30
THE STRUCTURE OF
they may be viewed by transmitted light, very
thin sections of them should be made. This may
be effected by means of a very sharp scalpel, or a
razor.. When objects are too small to be held
in the hand to be cut, they
may be placed between two
pieces of cork, and a section of
them made at the same time
that the cork is cut through.
Sometimes it is found desir-
able to unravel an object under
the Microscope. If this is the
case, only a low power should
be used, and the object may be
placed on a glass slide, without
any glass over, and two needles
with small wooden * handles
employed, — ordinary sewing
needles, with their eyes stuck
in the handle of a hair pencil,
will answer very well. (Fig. 14.)
Even when dissection is not
to be carried on under the
Microscope, a pair of needles
of this sort, for tearing minute
structures in pieces, will be
found very useful.
*&• 14< When opaque objects are
Dissecting Needles. to ^e examined, the light from
the mirror may be shut off, and the aid of the
bull's-eye condenser called in. The object being
secured in the forceps attached to the stage
(fig. 15), or laid upon a slide, the light is allowed
to fall on it through the condenser. (Fig. 9.) The
object-glass must be focussed in the same manner
as for transparent objects, till the best distance is
THE MICROSCOPE.
secured for examining it. The petals of plants,
the wings and other parts of insects, with many
other objects, can only be examined in this way.
Fig. 15. Stage Forceps.
Even the beginner will find it useful to keep by
him some little bottles, containing certain chemical
re-agents. Thus, a solution of iodine is useful to
apply to the tissues of plants, for the purpose of
ascertaining the presence of starch. This solution
may be made by adding five grains of iodine and
five grains of iodide of potassium to an ounce of
distilled water. It turns starch blue and cellulose
brown. Cellulose is the substance that forms the
walls of the cells in plants. Dilute sulphuric acid
(1 to 3) is also useful as a re-agent ; if applied to
cellulose previously stained with iodine, it imparts
a blue or violet tint. Strong nitric acid turns
albuminous matter a deep yellow; and when
diluted (1 to 4) with water is used for separating
the elementary tissues of vegetable substances either
by boiling or maceration.
The strong solution of potash (liquor potassse)
can also be employed with advantage in softening
and making clear opaque animal and vegetable
substances. While using these powerful agents,
great care should be taken to prevent the trans-
parency of the object-glass becoming impaired by
contact with them or by long exposure to their
vapours.
A HALF HOUR WITH THE
CHAPTER II.
A HALF-HOUR WITH THE MICROSCOPE
IN THE GARDEN.
AMOXGST the objects which can be examined by
the Microscope, none are more easily obtained than
plants. All who have a Microscope may not be
fortunate enough to have a garden ; but plants are
easily obtained, and even the Londoner has access
to an unbounded store in Coven t Garden. We
will, then, commence our microscopic studies with
plants. On no department of nature has the
Microscope thrown more light than on the struc-
ture of plants ; and we will endeavour to study
these in such a manner as to show the importance
of the discoveries that have been made by the aid
of this instrument.
If we take, now, a portion of a plant, the thin
section of an apple, or a portion of the coloured
parts of a flower, or a section of a leaf, and place
it, with a little water, on a glass slide under the
Microscope, we shall see that these parts are com-
posed of little roundish hollow bodies, sometimes
pressed closely together, and sometimes loose,
assuming very various shapes. These hollow
bodies are called " cells," jand we shall find that all
parts of plants are built tip of cells. Sometimes,
however, they have so far lost their cellular shape
that we cannot recognize it at all. Nevertheless,
all the parts we see are formed out of cells. Cells
tolerably round, and not pressed on each other,
may be seen in most pulpy fruits. In fact, with
a little care in making a thin section, and placing
PLATE
° XL
TuffeaWest sc adnat.
London. Tbfcert Sardmcte,
MICROSCOPE IN THE GARDEN. 33
it under the Microscope, the cellular structure of
plants may be observed in all their soft parts.
If, now, we take a thin section from an apple, or
other soft fruit, or from a growing bud, or tuberous
root, as the turnip, we shall find that many of the
cells contain in their interior a " nucleus," or
central spot, a representation of which is seen
from the cells of an apple in figure 1 of the first
plate. This nucleus is a* point of great import-
ance in the history of the cell, for it has been
found that the cell originates with it, and that all
cells are either formed from a nucleus of this kind,
or by the division of a thin membrane in the inte-
rior of the cell, which represents the nucleus, and
is called a " primordial utricle."
When the cells of plants have thus originated,
they either remain free or only slightly adherent to
each other, or they press upon each other, assuming
a variety of shapes ; they then form what is called
a " tissue." When cells are equally pressed on all
sides, they form twelve-sided figures, which, when
cut through, present hexagonal spaces. This may
be seen in the pith of most plants, more especially
the common elder, which is seen at figure 2 of
plate 1. Transverse slices of the stems of any
kind of plant from the garden may be made by a
razor, or sharp penknife, and will afford interesting
objects for the Microscope.
Cells, during their growth, assume a variety of
shapes, and the tissues which they form are named
accordingly. Two examples of such cells will be
seen in figures 243 and 244 in plate 8, where the
first represent cells from the hard shell of a plum
stone, and the second the thin cells from the out-
side of the seed of the guelder rose. 'Sometimes the
cells are very much elongated, or they unite together
to form an elongated tube ; the tissue thus formed is
34 A HALF HOUR AVITII THE
called " vascular tissue ;" but where tlie cells retain
their primitive form, it is called " cellular tissue." A
very interesting form of the latter is the " stellate"
tissue found in most water plants, and especially
regularly developed in the common rush, a represen-
tation of which is given in figure 3 plate 1. The
object of this tissue is, evidently, to allow of the
existence of a large quantity of air in the spaces
between the cells j by which means the stem of
the plant is lightened, and it is better adapted for
growth in water.
If the leaf of any plant is examined, it will be
found that on the external surface there is a thin
layer, called, after the thin external membrane in
animals, the " epidermis." This layer is composed
of very minute cells — smaller than those in other
parts of the plant, and when placed under the
Microscope, presents a variety of forms of cellular
tissue. The form of epidermal cells from various
plants is seen in figure 42 and the following
figures in plate 2. There is found in this layer a
peculiar organ which exists on the outside of all
parts of plants, and which demands attention. In
the midst of the tissue, at very varying distances,
are placed little openings, having a semilunar cell
on each side. These openings are called " sto-
mates," and can be well seen in the leaf of the
hyacinth, which is shown in figure 42, where the
cells of the epidermis are transparent ; but the
little cells which form the stomate are filled with
green colouring-matter. The stomates vary very
much in size and in numbers. They are found in
larger numbers on the lower than on the upper
side of leaves. In the common water-cress they
are very small, as seen in figure 43, plate 2, and
the cells of the epidermis are sinuous. The sto-
mates are found on all plants having an epidermis.
MICROSCOPE IN THE GARDEN. 3g
In figures 44 and 46 they are represented from
the wheat and the aloe. In the latter plant the
cells of the cuticle are very much thickened.
They can also be seen on the cuticle of the fruit,
as shown from the holly in figure 241, plate 8,
and also on the organs and petals. These form a
beautiful object under the Microscope. The petal
of the common scarlet geranium (Pelargonium)
affords a beautiful instance of the way in which
the cells of plants become marked, by their pecu-
liar method of growth. This is illustrated in the
cells of the common red-flowered geranium at
figure 45, in plate 2.
The vascular tissue of plants is either plain or
marked in its interior. If we examine the ribs of
leaves, the green stems of plants, or a longitudinal
section of wood, elongated fibres, lying side by side,
are observed, as is seen in the case of the elder, at
figure 53, plate 2. This is what is called "lig-
neous" or "woody" tissue, and the greater part
of the wood and solid parts of plants are com-
posed of this tissue. Such tissue is seen upon
the shoots of the young vine in figure 249,
plate 8. The fibres mostly lie in bundles, and are
divided from each other by cellular tissue. This
latter, in the woody stems of trees, constitutes the
"medullary rays," which are seen in transverse
sections of stems, extending from the pith to the
bark. The difference observable in the distribution
of the woody fibres and the medullary rays renders
the examination of transverse sections of the stems
of plants a subject of much interest ; figure 54
and the following figures in plate 3, present the
appearances of thin sections of various kinds of
wood (figures 54, 55, 56, 57, plate 3). In the
transverse sections of stems of most plants,,
large open tubes are observed. This is seen in
D 2
36 A HALF-HOUR WITH THE
the case of the oak, figured at figure 55, plate 3.
These are called " ducts," Such dacts may be well
observed in the transverse section of the common
radish, as seen at figure 51, plate 2, and in other
roots. These ducts are often marked by pores, or
dots, and are hence called u dotted ducts." These
dots are the result of deposits in the interior of
the tube of which the duct is formed, and a great
variety of such markings are found in the interior
of vascular tissue. One of the most common
forms of marked vascular tissue is that which is
called glandular woody tissue, of which a figure is
given at 54, plate 3. This kind of tissue is found
in all plants belonging to the cone-bearing, or fir
tribe of plants. In order to discover it, recourse
need not be had to the garden for growing plants,
as every piece of furniture made of deal wood will
afford a ready means of obtaining a specimen. All
that is necessary to observe the little round disks
with a black dot in the middle is to make a thin
longitudinal section of a piece of deal, and place it
under a half or quarter-inch object-glass, when
they will be readily apparent. The application of
a drop of water on the slide, or immersing them
in Canada balsam, will bring out their structure
better.
If we take the leaf-stalk of a strawberry, or of
garden rhubarb, and make a transverse section all
round, nearly to the centre of the stalk, the lower
part will at last break off, but be still held to the
upper by very delicate threads. If we examine
these threads, we shall find that they are fibres
which have been left by the breaking of the vessel
in which they were contained : such fibres are seen
at figure 48, plate 2. These vessels are called
" spiral vessels," and are found in the stems and
leaves of many plants. They are seen rolled up aa
MICROSCOPE IN THE GARDEN. 37
found in the garden rhubarb, at figure 47, plate 2.
Sometimes these vessels are found branched, as in
the common chickweed, which is seen at figure 50,
plate 2. This arises from two spires coming in
contact with each other, and adhering. Occasion-
ally the spiral fibre breaks, or is absorbed at certain
points, leaving only a circular portion in the form
of a ring, as seen in a vessel from the root of
wheat at figure 49, plate 2. Such vessels are
called "annular," and may be observed in other
roots besides those of growing wheat, as in the
leaves of the garden rhubarb. A modification of
this kind of tissue is seen in the stems and roots
of ferns, in which the vessel assumes a many-sided
form. This kind of tissue is called " scalariform,"
or ladder-like, and is seen in figure 52, plate 2.
Sometimes the spiral fibre is free. This is repre-
sented at figure 250, plate 8, from the testa of the
seed of the wild sage.
The bark as well as the wood of trees affords the
same appearance under the Microscope. If a piece
of the bark of any plant be examined by means of
a very thin transparent section, and placed upon a
slide, and put under an inch or a half-inch object-
glass, the structure of the bark may be easily seen.
On the outside of all is the cuticle, or epidermis,
and under this lie two layers, composed, like the
cuticle, of cellular tissue ; but the inner layer,
before we come to the wood of the stem, is com-
posed of woody tissue. The cellular layer, next the
woody one, is often developed to a very great extent,
and then constitutes what we know by the name of
cork. The bark from which corks are made is
obtained from an oak tree which grows in the
Levant. If we make a very thin section of a cork,
its cellular structure can be easily made out. The
cells are almost cubical, and when submitted to the
A HALF-HOUR WITH THE
action of a little solution of caustic potash, they
may frequently be seen to be slightly pitted. This
is represented from cork in figure 59, plate 3.
Many of the structures which are described above
may be seen in common coal ; thus proving most
satisfactorily that this substance has been formed
from a decayed vegetation. A transverse and a
longitudinal section of coal is shown at figures 60
and 61, plate 3. The examination of coal, how-
ever, is by no means an easy task, and the hands
and fingers may be made very black, and the
Microscope very dirty, without any evident struc-
ture being made out. Some kinds of coal are
much better adapted for this purpose than others.
Sections may be made by grinding, or coal may be
submitted to the action of nitric acid till it is
sufficiently soft to be cut. The amateur will not
find it easy work to make sections of coal ; but
should he wish to try, he may fasten a piece on to
a slip of glass with Canada balsam, and when it
has become firmly fixed, he may rub it down on a
fine stone till it is sufficiently thin to allow its
structure to be seen under the Microscope. Coal
presents both vascular and cellular tissue. The
vascular tissue is, for the most part, of the glandular
woody kind ; thus leading to the inference that
the greater portion of the vegetation that supplied
the coal-beds belonged to the family of the firs.
The external forms of the tissues of plants
having been examined, we are now prepared to
regard their contents. In the interior of the cells
forming the roots and the growing parts of plants
will be observed a number of minute grains,
generally of a roundish form. If we make a thin
slice of a potato, these granules may be very ob-
viously seen, lying in the interior of the cells of
which the potato is composed, as seen at figure 64,
MICROSCOPE IN TI1E GARDEN. 39
plate 3. If we now take a drop of the solution of
iodine, and apply it to these cells full of granular
contents, we shall find that the granules assume a
deep-blue colour. This is the proof that they are
starch ; and as far as we at present know, no other
substance but starch has the power of assuming
this beautiful blue colour under the influence of
iodine. We have thus a ready means at all times
of distinguishing starch. The grains of starch are
of various sizes and shapes. The starch of the
flour of wheat has a round form, and varies in size ;
that of the oat is characterized by the small
granules of starch adhering together in globular
shapes. When these globules are broken up, the
grains appear very irregular. Grains of wheat
starch and oat starch are seen in figures 62 and 63,
plate 3. In the arrow-root called " Tous les
Mois," the grains of starch are the largest known,
and, like those of the potato, they look as if com-
posed of a series of plates laid one upon the other,
gradually becoming smaller to the top. This is
seen at figure 65, plate 3. These lines do not,
however, indicate a series of plates, but appear
more like a series of contractions of a hollow vesicle
or bag. This vesicular appearance of starch may
be made apparent by gently heating it, after
moistening, over a spirit-lamp on a glass slide, or
by dropping on it a drop of strong sulphuric acid.
This action of the starch-granule appears to be duo
to the fact that the starch is converted into gum by
the action of the heat on the sulphuric acid. Sago
and tapioca are almost entirely composed of starch,
and may be easily examined under the Microscope.
Granules of sago are represented in figure 67, and
those of tapioca at figure 68 ; they are readily
distinguished by their size. The starch granules
are insoluble in water, but they are easily diffused
4-0 A HALF -HOUR WITH THE
through it ; so that by washing any vegetable tissue
containing starch, with water, and pouring it oft'
and allowing it to stand, the starch falls to the
bottom. This may be done by bruising the vege-
table tissue in a mortar, and then throwing it into
cold water. The tissue falls to the bottom, and
the starch is thus suspended in the water. In this
way the various kinds of starches may be procured
for microscopical examination. The granules of
starch have frequently a little black irregular spot
in their centre. In the starch of Indian corn it
assumes the form of a cross, which is seen at
figure 66, plate 3. Starch is a good object for
the use of the polarizing apparatus, which can be
applied to most compound Microscopes. The
grains of starch, under the influence of polarized
light, become coloured in a beautiful and peculiar
manner, permitting of great variation, as in the
case of all polarized objects.
If we take a little of the white juice from the
common dandelion, and put it under the Micro-
scope, we shall often see, besides the globules of
caoutchouc which make the juice milky, crystals
of various forms. Such crystals are called by the
botanist " raphides," — signifying their needle-like
form. They arise from the formation and accu-
mulation of insoluble salts in the fluids of the plant.
They are seen in various plants, and under very
•different circumstances. Beautiful needle-like crys-
tals can be seen in the juice of the common hyacinth,
represented at figure 69 ; the juice may be ob-
tained by pressing. A question has been raised as
to whether they are always formed in the cell. They
are mostly found lying in the cell, as in the leaves
of the common aloe, seen at figure 70, plate 3 :
they may also be found in the tissues of the com-
mon squill, and in the root of the iris. If a thin
PLATE '6.
itj^
MICROSCOPE IN THE GARDEN. 41
nection of the brown outer coat of the common
onion is made, small prismatic crystals are observed.
These are represented at figure 72, plate 3. Some-
times several of these crystals unite together around
a central mass, forming a stellate body. These
bodies have been called " crystal glands," but they
have no glandular properties. They may be seen
in the root and leaf-stalk of common rhubarb, and
may be easily observed in a bit of rhubarb from a
spring tart. From such a source, the drawing was
made at figure 71. These crystals are mostly
formed of oxalate of lime. They are constantly
found in plants producing oxalic acid. The gritty
nature of rhubarb root arises from the presence of
oxalate of lime. Sometimes the oxalate of lime
assumes a round dish-like form. Such forms are
seen in plants belonging to the cactus family. A
circular crystalline mass, as seen in a common
cactus, is represented at figure 73.
Other substances, besides oxalate of lime, are
found crystallized in the interior and on the surface
of plants. Crystals of sulphate of lime have been
found in the interior of cycadaceous plants. Car-
bonate of lime is found in crystals on the surface of
some species of Chara, or stonewort. There is a
shrub not uncommon in gardens, known by the
name of Deutzia scabra, on the under surface of
the leaves of which there are beautiful stellate
crystals of silica. The best way of seeing these is
to put the leaf under the Microscope, and to
examine it by the aid of reflected light.
Sugar and honey assume a crystalline form, and
may be known by the shape of their crystals. At
figure 238, plate 8, a crystal of honey is repre-
sented ; it is thinner and smaller than the crystal
of cane sugar represented at figure 239. Honey
is sometimes adulterated with sugar. Under these
42 A HALF-HOUR WITH THE
circumstances the sugar crystal loses its definite
outline, and assumes the form seen at figure 240.
The external surface of the parts of all plants
•will afford a rich field of amusement and instruc-
tion to the microscopic observer. The cuticle, or
epidermis, of which we have before spoken, has a
very varied structure, arid contains the little open-
ings (stomates) before described. The cuticle, which,
in a large number of cases, is smooth, becomes
elevated in some instances, and forms a series of
projections, which, according to their form, are
called " papillae," " warts," " hairs," " glands," and
" prickles." The papillae are slight elevations, con-
sisting of one, two, or more cells ; the warts are
larger and harder; whilst the hairs are long, the
glands contain a secretion, and the prickles are
hard and sharp. For examining the form and
growth of these hairs, the flowers of the common
pansy (heart's-ease) afford a good object. Some of
the projections are merely papillae, as in the case
of the kind of rudimentary hair represented in
figure 75, plate 3 ; others are found longer, and
more like hairs, as seen in figure 76 j whilst others
are long, and, the sides of the hair having contracted,
they assume the appearance of a knotted stick, as
seen in the hair from the throat of the flower of the
pansy, at figure 78. The family of grasses, wheat,
barley, oats, and other forms, are favourable sub-
jects for the examination of simple hairs, or hairs
composed of a single elongated cell. At figure 74,
a single hair is given from a common grass. All
that is necessary to be done, in order to see these
hairs, is to take any part of the plant where they
are present, and to slice off a small portion with a
sharp penknife or razor, and place it under the
Microscope. They may be either examined dry, or
a little water may be added, and a piece of thin
MICROSCOPE IN THE GARDEN. 43
glass placed over them on the slide. Hairs are
frequently formed of several cells. On the white
dead-nettle the hairs are composed of two cells, as
seen in figure 7 9 a. The nucleus, or cytoblast, is
often seen in these, and is represented in figures
76, 77, and 79, plate 3. On the common groundsel
hairs may be seen, composed of several cells, each
cell containing a nucleus, as at figure 795. Hairs
like a string of beads are found on the pimpernel
and sow-thistle, which last will be found in
figure 80, plate 3. Occasionally hairs become
branched. Thus, on the leaf of the common
chrysanthemum the hairs present the form of the
letter T. This hair is represented at figure 82.
On the under-surface of the leaves of the common
hollyhock hairs are seen with several branches,
giving them a stellated appearance, as seen at
figure 84. The common lavender is covered with
stellate hairs, as seen at figure S5a. These
hairs may be examined as opaque or transparent
objects, when immersed in a little glycerine.
The hair of the tobacco plant presents a peculiar
knobbed appearance. The presence of these hairs
is a test of the purity of tobacco. It is shown
in figure 81. The verbena has rosette -shaped
hairs, as in figure 83. Sometimes hairs are
covered over with little dots, which are supposed
to be deposited after the growth of the cells of
the hair. Such hairs may be seen in the common
verbena, and are represented at figure 856.
Hairs are sometimes loose and long, as in the
white poplar, seen at figure 86. Occasionally an
elevation, consisting of several cells, is formed at
the base of a hair. These are shown in figure 87.
When these cells contain a poisonous secretion,
which is transmitted along the tube of the hair, the
hair is called a glandular hair, or sting. Such are
44 A HALF-HOUR WITH THE
the hairs of the common stinging-nettle, represented
at figure SSa.
The hairs constituting the down or " pappus " of
compositous plants assume a variety of forms. The
seed or fruit of the common groundsel has a beau-
tiful crown, given at figure 245, in plate 8. The
pappus of the dandelion appears notched, as seen
at figure 246. The burdock has a cottony hair,
while the goatsbeard is like a feather, — both of
which are represented respectively in figures 247
and 248.
If a hair is examined in its growing state, with
an object-glass of one quarter of an inch focus, a
movement of the particles in its interior is often
observed. This is easily seen in the hairs around
the stamens of the common Spider wort (Trades-
cantia Virginica). Such movements are very com-
mon in the cells of water plants. One of those
most commonly cultivated in aquavivaria at the
present day, the Valisneria spiralis, affords the best
example of this interesting phenomenon. In order
to observe this movement, a growing leaf of the
valisneria should be taken, and a longitudinal slice
should be removed from its surface, by means of a
sharp penknife or razor. The slice, or the sliced
part left on the leaf, should now be put on a slide,
a drop or two of water added, and covered with a
thin piece of glass, when, after a little time, espe-
cially in a warm room, the movement will be ob-
served. This movement takes place in the little
particles around the sides of the cells represented
in figure 886, plate 3. It may also be seen in
the leaves of the new water- weed (Anacharis
alsinastrum), the frogbit, the rootlets of wheat, in
the family of charas, and in the cells of many other
water plants. In examining some species of Chara,
the external bark, or rind, should be removed from
MICHOSCOPE IX THE GARDEN. 45
the cells, or the movements will not be seen. This
movement seems dependent on the internal proto-
plasmic matter, or " primordial utricle," which is
contained in many cells, and which, in these cases,
is spread over the interior of the cell. It is, how-
ever, capable of contraction, and when the plants
are exposed to cold, the utricles contract and pre-
vent the movement of the contents in the interior.
It is, apparently, the extension of this substance
beyond the walls of the cell which constitutes the
little hairlike organs called " cilia," which are con-
stantly moving, and by the aid of which the spores
of some plants effect rapid movements. Such
organs are found in the Pandorina Morum and
Volvox globator, moveable plants represented at
figures 13 and 14, plate 1. The effect of these
cilia in producing the movements of plants is well
seen in the Volvox globator, which, on account of
its rapid movements, was at one time regarded as
an animalcule, but it is now regarded as a plant.
Cilia are, however, more frequently met with in the
animal kingdom. They are seen in the drawing of
Plumatella repens, at a, in figure 163 of plate 6.
Amongst the parts of plants which can alone
be investigated by the Microscope are the stamens.
These organs are situated in the flower, between
the petals and the pistil, and usually consist of a
filament, or stalk, with a knob or anther at its top.
If the anther is examined, it will usually be found
to consist of two separate valves, or cases, in each
of which is contained a quantity of powder, or dust,
called " pollen." The walls of these valves are
worth careful examination under the Microscope,
on account of the beautifully-marked cellular tissue
of which their inner walls consist. The cells of this
tissue contain in their interior spiral fibres similar
to those which have been described as present in
46 A HALF HOUR WITH THE
certain forms of vascular tissue. In the anthers of
the common furze the fibres are well marked, and
are represented in figure 118, plate 5 ; in the
common hyacinth they are larger, and frequently
present, in their intercellular spaces, bundles of
raphides, as seen at Figure 119. In the white
dead-nettle the fibre is irregularly deposited, as at
figure 120. In the anthers of the narcissus, given
at figure 121, the cells are almost vascular in their
structure, and present the same appearance as
those described under the head of annular ducts.
The reader should compare figure 121, plate 5,
with figure 49, plate 2. In the crown imperial
the fibres of the cells radiate from a central point
in a stellate manner, as at figure 122.
When the anther-cases have been examined, a
little of the dust may be shaken on to a slide, and
examined as an opaque or a transparent object.
Each species of plant produces its own peculiar
form of pollen. These little grains are actual cells.
They are the cells of plants which in their position
in the anther will not grow any further. They are
destined to be carried into the pistil, where, meet-
ing with other cells, they furnish a stimulus to their
growth, and the embryo, or young plant, is pro-
duced. The history cf the development of these
cells, as well as of those in the interior of the pistil,
is a very interesting one, and is one of those sub-
jects of investigation which has been created by
the aid of the Microscope. The pollen grains vary
in size as well as form. They are frequently oval,
as seen in figure 123, plate 5. In the hazel and
many of the grasses they are triangular. Those
from the hazel are represented at figure 124. In
the heath they are tri-lobed, as at figure 125 ; in
the dandelion, and many of the compositous order
of plants, they are beautifully sculptured, as seen
MICROSCOPE IN THE GARDEN. 47
at figure 126. IB the passion-flower, three rings
are observed upon them, as though they had been
formed with a turner's lathe — figured at 127. In
the common mallow, they are covered all over with
little sharp-pointed projections, like a hand-grenade.
These are represented at figure 128. The micro-
scopic observer should make himself acquainted
with the forms of pollen grains, as, on account of
their small size and lightness, they are blown about
in all directions, and may be found on very dif-
ferent objects from those in which they have been
produced. Some absurd mistakes have been com-
mitted by confounding pollen grains with other
forms of organic matter. Thus, pollen grains in
bread were regarded as bodies connected with the
production of cholera.
The pistil, which is the central organ seated in
the midst- of the stamens in the flower of plants,
will afford a great variety of interesting points for
examination with the Microscope. In the earliest
stages of the growth of the pistil, thin sections of
it may be made, and the position of the ovules
observed. In the ovule will be found the embryo
sac, a central cell, which, on being brought in
contact with the pollen grain, grows into the seed.
The seed contains the embryo, or young plant. In
most plants this is sufficiently large to be seen
by the naked eye ; but it may, nevertheless, be
examined with advantage by a low microscopic
power The seed is covered on the outside with
a membrane, which is called the " testa." This
membrane is often curiously marked, and the whole
seed may be examined as an opaque object with
the low powers of the Microscope. In order to do
this, the light must be shut oft" from the mirror,
and, the object being placed on the stage, a pencil
of light should be thrown upon it by the aid of the
43 A nALF-nora WITH TEE
bull's-eye condenser. If a seed of the red poppy
be now examined, it will be found to have a
uniform shape, and to be reticulated on its surface,
as seen at figure 129, plate 5. The seed of the
black mustard exhibits a surface apparently covered
with a delicate network, seen at figure 130. Some
seeds have deep and curved furrows on their sur-
faces, such as exhibited in figure 131. The great
snapdragon has a seed covered with irregular
projecting ridges, having a granuled appearance,
represented at figure 132. The seed of the chick-
weed presents a series of blunt projections, as in
figure 133. In the various forms of umbel-
bearing plants, the seeds adhere to the fruit, and
the fruit is commonly called the " seed." Such
are caraway, coriander, dill, and anise seeds. The
plants of this family are very common weeds in
our gardens and fields, and may be easily procured
for microscopic examination. Some of these fruits
are covered over with little hooks, seen at figure
134, whilst others present variously -formed ridges
and furrows, which are amongst the best means
for distinguishing these plants the one from the
other.
PhAIE 4
London Robert
MICROSCOPE IN THE COUNTRY. 49
CHAPTER III.
A HALF-HOUR WITH THE MICROSCOPE
IN THE COUNTRY.
A COMPOUND Microscope is not easily conveyed and
put up in the fields, but the produce of the roads
and waysides may be easily brought to the Micro-
scope at home. No one who has a Microscope
should walk out into the country without supply-
ing himself with a few small boxes, a hand- net,
and three or four small bottles, in order to bring
home objects for examination. The dry produce,
which may be put into boxes, is of a different
character from that which may be conveyed home
in bottles. We shall, therefore, first direct attention
to the minute forms of mosses, fungi, lichens, and
ferns, which may be collected in boxes ; premising,
however, that many members of these families may
be found without going into the country to seek for
them. The cheese in the pantry, and the decayed
parts of fruits, and objects covered with mould, are
good subjects for microscopic examination.
Amongst the minuter plants and animals whose
true nature can only be detected by the Microscope
many are composed of a single cell, whilst others,
like higher plants and animals, are formed by the
union of a large number of cells. The greater
proportion of the one -celled, or unicellular plants,
as they are called, are found in water : but some
are found on moist rocks, stones, and old walls.
Amongst these there is one of exceedingly simple
structure, called gory dew (Palmdla cruenta). This
•50 A HALF-HOUB WITII THE
plant appears as a red stain upon the surface of
damp objects. If a little of this red matter is
scraped off the object to which it is attached, and
placed under the Microscope, it will be found to
consist of a number of separate minute cells, as
represented at figure 89, plate 4. This plant
belongs to the same family as the red-snow plant,
ard there are a number of forms of these minute
organisms, which, on account of their rapid growth
and red colour, have given rise to alarming appre-
hensions, in former times, when their true nature
was imperfectly understood. One of them attacks
bread, and gives to it the appearance of having
been dipped in blood. They also attack potatoes.
Of the same simple structure, but not having a red
colour, is the yeast-plant, or fungus, shown at
figure 90, plate 4. This plant abounds in yeast,
and may also be found in porter and ale. If
vinegar is allowed to stand for some time, a
minute plant is developed, called the vinegar-
plant. In its earlier stages of growth it exhibits
elongated cells, looking like broken pieces of
thread, seen at figure 91. Threads more fully
developed are often seen in decomposing fluids,
and upon the surface of decomposing animal and
vegetable substances ; such is the so-called cholera-
fungus, which may be obtained by exposing damp
slides to the air. They are shown at figure 92.
Such plant-like threads can be collected from the
air in clamp and unwholesome cellars and rooms,
and were at one time supposed to be connected
with the production of that fearful disease, the
cholera. It has been rendered, however, exceed-
ingly probable that all these appearances are but
different forms of the fungus which produces
common mould, and which is known by the name
of Penicillium glaucum. This fungus is represented
MICROSCOPE IN THE COUNTRY. 51
at figure 95. It may be found on the surface of
preserves and jellies, and consists of a mass of fila-
ments or threads serving as its base, from the
surface of which individual filaments rise up, bear-
ing a number of minute cells, which are the
spores, or reproductive organs. These are seen at
figure 96.
Plants such as these, and belonging to the family
of fungi, are found everywhere on the leaves of
plants in the summer and autumn, forming irre-
gular spots, of a yellow, red, or black colour. If
such leaves are brought home and placed under the
Microscope, they present a never-failing source of
interest. The red appearance on the leaves of
wheat, called the rust, is due to one of these fungi,
seen at figure 93, plate 4. This appears to be an
early stage of the fungus, which produces what is
called mildew, and is represented at figure 94.
These fungi are so common on the wheat-plant
that their spores mingle with the seeds when
ground into flour, and can be found, when care-
fully sought for, in almost every piece of bread
that is examined under the Microscope. Mouldy
grapes, pears, apples, and other fruits, present fungi,
having the same general form as that of common
mould. Such a fungus is the Botrytis of mouldy
grapes seen at figure 96. Mouldy bread also pre-
sents a fungus of this kind. This species is called
Mucor mucedo, and is represented at figure 97. Its
spores are arranged in a globular form. A fungus
not unlike the last has been described as growing
in the human ear, and is figured at 98. The
leaves of the common bramble present a fungus
in which the spores are arranged on a more dense
and elongated head. This is called Phragmidium
bulbosum, and is represented at figure 99. The
Outturn which attends the blight of the vine, seen
E 2
52 A HALF-HOUR WITH THE
at figure 100, and the Botrytis which accompanies
the potato disease, figure 101, are other and in-
teresting forms of these minute parasites. The
common pea is subject to a blight which is ac-
companied by a peculiar fungus, seen at figure 102a,
which, when examined by a low power, presents a
globular mass, surrounded by minute filaments.
Under a high power the central ball is resolved
into a series of little cases, containing in their
interior the minute spores. These are seen at
figure 1026. Seeds, as well as fruits, are liable to
the attacks of fungi during their decay. Figure 103.
Plate 4, represents a fungus found in a mould upon
a common Spanish nut. This fungus looks like a
red powder spread over the surface of the nut. A
fungus has been described as attacking the oil-
casks in the London docks : its fibres resemble
threads of black silk. It is represented at
figure 104. The spores are found scattered about
the fibres. As we have already seen, fungi are
found on the human body, and accompany certain
forms of disease of the skin, more especially those
of the head. In these cases the fungi insert them-
selves into the follicle of the hair, and introduce
themselves into its structure, so that it either falls
off or becomes disorganized. The fungus of ring-
worm, called Achorion Schonlenii, is given at
figuie 105. If the seed of wheat is allowed to
germinate in a damp place, the little rootlet which
it sends down will be found covered over with a
minute fungus. A fungus of some interest, on
account of its unusual place of growth, may
be found, in autumn, attached to the roots of
the common duck-weed (Lemna minor), seen at
figure 106 — plate 4. In the same figure, at «,
is represented a fungus of a different kind, it is
parasitic within the cells, and has a bead-liko
MICROSCOPE IN THE COUNTRY. 53
appearance. It may be an earlier stage of the
growth of the former.
The microscopic structure of the higher forms of
fungi is not without its interest. In the fungi a
very elongated form of cellular tissue frequently
occurs, and in the stem of the common mushroom
it will be seen to be branched, as at figure 103.
The looser portions of the fibres of the mushroom,
which are found in the earth at the bottom of the
stem, afford even a better illustration of this struc-
ture, and is given at figure 107. The gills of the
mushroom, when put under the Microscope, display
a number of small projections surmounted with
four round cells ; these are the spores arranged in
fours, and which, on that account, are called tetra-
S2)ores. They are seen at c, figure 107.
In the woods, in winter time, fungi abound, and
their parts may be examined under the Microscope
with great interest. Amongst the winter beauties
of the forest, none are more attractive than the
various forms of peziza, or cup-moulds. If a section
be made through one of the cups of these beautiful
fungi, they will present the appearance drawn in
figure 108, plate 4. A series of hollow elongated
cases will be found lying between compressed elon-
gated tissue. In these cases a series of rather oval
minute cells will be found, which are the spores of
the peziza. If these are magnified with a higher
power, they will be seen to be covered over with
minute spines, as seen at a.
Amongst the objects which more especially
attract the attention of observers in the country,
in winter time, are the various forms of lichens,
which grow parasitic upon the bark of trees. There
is one of a yellow colour, which spreads on palings
and the barks of trees, like dried pieces of yellow-
paper. At the surface of the membranous scales of
54 A HALF-HOUR WITH THE
which the plant is composed will be found deeper
yellow spots. If one of these is cut through, and a
thin section placed under the Microscope, it will be
found to possess very similar organs to the peziza.
A series of cases will be found, containing the
minute spores by means of which the plant is
reproduced. These cases, called asci, are figured
at. 109.
A walk across a damp uncultivated piece of ground
will not fail to reveal some spots which are boggy,
Here the bog-moss (Sphagnum} must be looked for,
and when found, it may be regarded as a good
illustration of the family of mosses, and portions
preserved for microscopic examination. The leaves
afford interesting examples of fibro-cellular tissue,
as seen at figure 110; and this tissue may be
examined from day to day, as affording an illus-
tration of the process of development in vegetable
tissue. Other forms of mosses may be found on
banks, old walls, rocks, and crevices. The organs
which produce the spores, or seeds, are well de-
serving the attention of the microscopic observer.
These represent the pistils in the higher plants.
The organs which represent the stamens are also
very interesting, but they are not so easily pro-
cured. We therefore proceed to describe the
spore-bearing organ. This may be easily seen with
the naked eye, although its beauties cannot be
brought fully out without the aid of the Micro-
scope. The part which contains the spores is
seated on a little stalk, and is called the " urn,"
and is represented in figure 112. Covering the
urn, and fitting on to it like a nightcap, is the
calyptra, marked a. On slipping off the calyptra,
a conical body fitting into the urn is observed, and
this is called the "operculum" (b). If the operculum
is now lifted offt there is revealed, below, a series of
MICROSCOPE IN THE COUNTRY.
twisted hair-like threads (c), which are called the
" peristome." These processes are held together by
minute teeth (d). The spores (e) are found in the
interior of the urn. All these parts are subject to
great varieties in different kinds of mosses.
.From the mosses we may pass on to the feins.
Like the mosses, they have no regular flowers, and
the parts which correspond to the urns of the
mosses are the small brown scaly-looking bodies
seated on the back of the fronds, or leaves. In the
male fern the little brown bodies which contain
the spores are round, as seen in figure 113, and in
the common brakes they are placed on the edge of
the fronds, as at figure 114. These organs, which
are called " sori," may be easily seen as opaque
objects, under the lower powers of the Microscope.
In the common hart's-tongue, or scolopendrium,
the sori are arranged in elongated bands. In this
case the sori are covered with a membrane called
an " indusium." On opening this, the sori are
found lying close together. Each one of these sori
is found to be made up of a number of cases called
capsules, or " thecae," attached to a stalk by which
they are fixed to the frond. This organ is seen at
figure 115. These thecse are beautiful objects
under the Microscope. Springing from the top of
the stalk is a series of cells which surround the
case, forming what is called the rt annulus." This
ring possesses an elastic power ; so that when it
breaks, the capsule is torn open, and the spores
in the inside escape. The spores are covered over
with little spines, as at a, in the same figure. The
spores of ferns are often called seeds, but they are
more like buds than seeds. If one of these spores
is watched during its growth, it will be found that
it grows into a little green membranous expansion,
on the surface of which the two sets of organs
56 A HALF-HOUR WITH THE
resembling the pollen grains and ovules of the
higher plants are developed. The representatives
of the pollen grains are little moving bodies, re-
sembling animalcules, which pass over the surface
of the membranous expansion till they reach the
ovules, or true spores of the fern, which they fer-
tilize, and the young plant then shoots forth. The
ferns, of which so many species may be found in a
walk in the country, or cultivated in a Ward's
case in town, are worthy the minute attention of
the possessor of a Microscope, on account of the
great variety of forms which their organs of fructi-
fication present.
The club-mosses are found on boggy moors and
open places, and present a variety in the forms of
their fructification. The reproductive organs are
formed out of a transformed branch, and are found
lying at the base of scale-like bodies, resembling
the scales which form the fruit of firs and pine-
trees, as seen at figure 115, a. The spores of the
club-mosses are of two kinds, large and small ;
hence they are called " megaspores " and " micro-
spores." The last are very minute, and when
highly magnified, they present a reticulated ap-
pearance. The spores are seen at b and c in
figure 117. In the interior of these spores is a
minute worm-like body, which acts the part of the
pollen in higher plants. The megaspores are much
larger. They represent the spores of ferns, and
produce an expanded membrane, on which grow
the true representatives of the ovules, which
coming in contact with the microspores, new plants
are produced.
Another family of these flowerless plants, which
has yielded highly interesting results to the micro-
scopic observer is the group of horsetails. If these
are gathered in the spring of the year, they will
I
London : Hbbert Ha.rcJmcke,1860/,
MICROSCOPE IN THE COUNTRY. 57
present two forms ; one showing the leaves and
green parts of the fruit ; the other, the leaves
changed into reproductive organs. These may be
very easily examined as opaque objects under the
Microscope. The spores are seated on round shield-
like disks, represented in plate 4, at figure 116, a.
When the spores are examined by a higher power,
they present four spiral filaments, which are twisted
round the body of the spore, and seen at b. If the
spore is breathed upon whilst under the Microscope,
the spiral filaments gradually relax their grasp, and
they become expanded and attached to the spore
only at one end, as represented at c. The cuticles
of the Equisetums are strongly siliceous, and are
very curious and interesting objects, and will repay
the trouble taken in preparing them. This may
be done by boiling a piece of the stem, in nitric
acid and chlorate of potash, and, after washing the
detached cuticle, transferring it to absolute alcohol,
from thence to oil of cloves, and afterwards
mounting in Canada balsam.
The study of the flowerless plants is one of
never-ceasing interest. Within the last few yeare
much has been done by the aid of the Microscope
to clear away the mystery which surrounded the
functions performed by certain organs they possess.
Much more, however, remains to be done ; and an
interesting field is still open to the inquiries of the
microscopist. We will now, however, take our
Microscope to the pond-side, where we shall still
find many plants to interest us, belonging to the
lower, or flowerless groups together with animals,
the companions of their aqaatic life, and the repre-
sentatives of their simpler mode of existence.
58 A HALF-HOUR WITH THE
CHAPTER IT.
A HALF-HOUR WITH THE MICROSCOPE
AT THE POND-SIDE.
CISTERNS, ditches, ponds, and rivers, contain nume-
rous objects to interest the microscopic observer.
Some of these objects float on the surface of the
water ; others are found swimming about in the
midst of the water ; whilst the greater number
are found at the bottom. In collecting objects
from fresh water, little bottles may be used, and a
common spoon or small net employed for collecting
them. Where the objects are only few, large
quantities of the water should be allowed to stand,
and the whole poured off, with the exception of a
table-spoonful or two, which may be then placed
in a wine-glass. A little of the sediment may be
taken up in a pipette or clipping-tube, and con-
veyed to the animalcule-cage, and the cover having
been put on, it may be placed under the Micro-
scope. If the objects are moving about too rapidly,
the cover may be pressed down till they are secured.
They may be first sought out with a low power,
and when it is wished to examine them more
closely, a higher power may be put on.
Of all the forms of microscopic plants which
are found in fresh water, those belonging to the
families of desmids and diatoms are most interest-
ing. We have already spoken ot plants consisting
of one cell, and these also consist of one cell ; but
they have this peculiarity, that their cells are
divided into two equal parts, each part having the
same form as the other. The desmids are dis-
MICROSCOPE AT THE POND-SIDE. 59
tinguished from the diatoms by their bright-green
colour, and by their cells not depositing silex, or
flinty matter, as is the case with the latter. The
siliceous nature of the shells of diatoms is made
apparent by their not being acted on by strong
acids, as nitric and hydrochloric.
The desmids sometimes abound in ditches and
small pieces of standing water. Amongst other
objects in a drop of water they are easily recog-
nized by their beautiful bilateral forms and dark-
green colour. One o-f the most charming of these
is named Euastrum, and consists of two notched
halves of a bright-green colour, with darker green
spots. It is represented at figure 28, plate 2.
The green matter is composed of a waxy substance,
called chlorophyle, and is the same matter as that
which produces the green colour of leaves. Some
of the desmids assume a lunate form, and are
named Closterium, a species of which is figured
at 29, plate 2. There are various species of Clo-
sterium, all of the same general form, and occa-
sionally occurring in very great abundance. Some-
times several of the cells are attached together,
forming a long chain, as in the genus Desmidium,
seen at figure 30, from which the family takes its
name. These break up and go on growing. When
they grow, the new cells are formed between the
two halves of the parent cells. This is represented
at figures 136 and 137, plate 5. In a genus
called Scenedesmus, several cells are united, and
the two last halves are furnished with horns, as
seen at figure 32 ; at other times several cells
unite, forming a globular mass, as in Pediastrum,
represented at figure 31. In this case each cell
presents two projections, forming objects of singular
beauty.
The diatoms are more numerous and widely
60 A HALF-HOUK WITH THE
diffused than the desmids. The lattei are decom-
posed, and their bodies perish when they die ; but
from the fact that the diatoms deposit silex in
their structure, they are almost imperishable. They
are found in great abundance in the mud of rivers,
ponds, and lakes. They are also present in those
deposits of clay which once formed the bed of
rivers and lakes, and which are now dry. In
order to procure the diatoms from these deposits,
ihe clay or earth should be well washed with pure
water, and the deposit allowed to subside, and the
water poured off. This may be repeated several
times. The deposit is then to be washed with
hydrochloric acid, and when the effervescence is
over, the acid is poured off, and a fresh portion is
added. This may be repeated several times, and
when the hydrochloric acid ceases to act, nitric
acid may be employed in the same manner. When
no action occurs by its use cold, the deposit may
be transferred to a watch-glass, and kept over a
spirit-lamp, at a temperature of about 200°, for
three or four hours. The deposit must then be
well washed with pure water, to remove all the
acid. The deposit will be found now to consist
almost entirely of diatoms. If anything else be
found, it will be grains of sand. By casting the
deposit into a small quantity of water, and allow-
ing the heaviest particles alone to subside, these
will be generally found to contain the sand and
larger diatoms. By repeating this process suc-
cessively, the deposits consist gradually of smaller
and smaller diatoms, which may be examined with
gradually higher powers, in proportion to their
minuteness. Some are perfectly round, as in the
case of the genus Coscinodiscus, a species of which
is figured at 38, plate 2. It is marked beautifully
over their surface ; others are triangular : some are
MICROSCOPE AT THE POND-SIDE. 61
square, and attached together. The last form is
seen in Melosira, species of which are figured
at 36 and 37, plate 2, and 139, plate 5. The
most common forms are those which are oval, or
boat-shaped, and represented by species of Pin-
nularia and Navicula in figures 34 and 35 a, in
plate 2. Some of these are again larger at one
end than the other, as in Surirella, figure 33.
The markings upon the surface are very various.
In some forms the markings are exceedingly
minute : so small are they, that certain species
of diatoms have been used as test objects, for
testing the highest powers of the Microscope.
Whilst living, the diatoms possess the power of
moving about, and in some of them, as well as the
desinids, a movement has been observed of the
small particles in their interior. The diatoms are
generally of a brownish or brownish-yellow colour,
which seems to be due to a small quantity of iron
in their composition. They are increased in the
yame way as the desmids, by the production of new
cells between the parent frustules. This process
is seen in figure 3o, a and &, in plate 2. The
continuance of the species in these organisms is
secured by the process of conjugation and the sub-
sequent formation of the spores. This process is
exhibited in figures 13o and 136, plate 5. In some
cases, however, the spore is found without the union
of two cells, as in Melosira represented at figure 137,
plate 5.
Sometimes, attached to the bottom of a pond or
river, or growing from immersed objects, or floating
about in the water, will be found long green fila-
ments. These are the fronds of confervse. All
forms of these — and they are very numerous — will
be found most beautiful objects for examination.
They may be laid on a slip of glass in water, and
€ A HALF-HOUR WITH THE
covered over with a piece of thin glass ; or they
may be placed in the animalcule-cage. They con-
sist of a series of cells growing end to end, and
their partition- walls can be easily seen. They are
of a green colour, from the chlorophyle contained
in their interior. In the case of the yoke-threads,
the chlorophyle is frequently arranged in a spiral
manner along the interior of the filament, as in the
Zyynema represented at figure 11, plate 1. These
yoke-threads may be often seen to unite with each
other, and the contents of one cell are emptied into
the other, forming the spore of the plant, as seen
at figure 135, plate o. The cell contents some-
times break up into smaller portions, called
zoospores, which, when they escape from the cell in
which they are contained, move about with great
rapidity. This is seen in figure 11, plate 1, at
a and b. The moving power of the lower plants
is well seen in the division of these confervse, called
Osdtiatorias, which are sometimes found in semi-
putrid water. A species is figured at 12, plate 1.
As they lie upon the glass slide they will be seen
to move over each other in all directions : hence
their name.
Some of the spores formed by the confervse move
about by the agency of little organs called cilia.
These are extensions of the motile matter of the
cell, and are found very commonly in the animal
kingdom. Occasionally, a number of these ciliated
spores are aggregated together, forming a rapidly-
moving sphere. Of this the Pandorina Moruni
affords a good example, seen at figure 13, plate 1,
in which each spore possesses two cilia. But the
most remarkable of this kind of moving plant is the
Volvox globator, represented in figure 14 of the
same plate. This beautiful moving plant was at
one time thought to be an animalcule, but it is now
MICROSCOPE AT THE POND-SIDE. 63
regarded as a true plant. It consists of a large
number of spores, or cells, each having two cilia,
and connected together by a delicate network of
threads. In the interior of this moving sphere are
seen smaller globular masses, of a dark-green colour,
which are the young of the volvox, which have not
yet developed the network, by means of which their
spores are separated, and their ciliated ends pre-
sented to the water, and by means of which their
movements are effected.
Another form which is now regarded as a loco-
motive plant is the Euglena viridis, seen at figure
15, plate 1. It is often found in prodigious num-
bers, giving to "water the appearance of green-pea
soup. When placed under the Microscope, it fre-
quently presents a red speck, or point, at one end,
and an elongated tail at the other. The red spot
has been regarded as an eye ; but if it is watched,
it will be found the red colour will often extend
from the red spot to the rest of the body ; and it
is probable that the red colour is only a change in
the condition of the chlorophyle contained in its
interior. Amongst this class of plants it is not
unfrequent for the chlorophyle to assume a red
colour at certain stages of its growth.
The transition from the filamentous to the mem-
branous form of these plants is well seen in the
species of Viva. These are found in both fresh and
sea water. In the early stages of its growth, the
ulva presents the filamentous form of a conferva,
as seen at a, in figure 26, plate 2. Gradually the
cells of the filament split up into two or three
seams (b) j and this goes on till at last a broad flat
membrane is produced (c).
If the plants of our fresh waters are interesting,
not less so are the animalcules ; for, just as we
have one -celled plants so we have one-celled ani-
64 A HALF-HOUR WITH THE
mals, and it was only by the aid of the Microscope
that they were discovered and can be examined.
Wherever the above plants are found, there will
also be discovered animals to feed upon them. The
animal is distinguished from the plant by its feed-
ing on plants, whilst the latter feed on inorganic
substances.
There is considerable difficulty in at once dis-
tinguishing between the lowest forms of animals
and plants. Although the animal generally pos-
sesses a mouth, and a stomach in which to digest
its vegetable food, there are some forms of animal
life so simple as not to possess either of these
organs. In the sediment from ponds and rivers
there will frequently be found small irregular
masses of living, moving matter. If these are
watched, they will be found to move about and
change their form constantly. As they press them-
selves slowly along, small portions of vegetable
matter, or occasionally a diatom, mix, apparently,
with their substance. Cells are produced in their
interior, which bud off from the parent, and lead
the same life. These creatures are called amsebas,
and are represented in our first plate, figure 16.
Although they have no mouth or stomach, they are
referred to the animal kingdom. They appear to
consist entirely of the formative matter found in
the interior of all cells called moto planes or
sarcode without any cell-wall. If we suppose an
amoeba to assume the form of a disk, and to send
forth tentacles, or minute elongated processes from
all sides, v:e should have the sun animalcule
(ActinopJirys Sol), which is represented at figure
17, plate 1. This curious creature has the power,
apparently, of suddenly contracting its tentacles,
and thus leaping about in the water. It can also
contract its tentacles over particles of starch and
MICROSCOPE AT THE POND -SIDE. 65
animalcules, and press them into the fleshy sub-
stance in its centre. This is undoubtedly an animal,
but it has no mouth or stomach. A large number
of such forms present themselves under the Micro-
scope. Some of them are covered with an external
envelope, which they make artificially, by attaching
small stones and other substances to their external
surface, as in the case of the Difflugiae, seen at
figure 18, plate 1 ; or they may form a regular
case, or carapace, consisting of a hairy membrane,
as in Arcella, represented at figure 19. We shall
meet again with forms resembling these when wo
take our Microscope to the sea- side.
One of the most common animalcules met with
in fresh water, and whose presence can easily be
insured by steeping a few stalks of hay in a glass
of water, is the bell-shaped animalcule. These
animalcules, which are called Vorticetta, are of
various sizes. Some are so large that their presence
can easily be detected by the naked eye, whilst
others require the highest powers of the Micro-
scope. They are all distinguished by having a
little cup-shaped body, which is placed upon a long
stalk, figured at 40, in our second plate. The stalk
has the peculiar power of contracting in a spiral
manner, which the creature does when anything
disturbs it in the slightest manner. In some species
these stalks are branched, so that hundreds of these
creatures are found on a single stem, forming an
exceedingly beautiful object with the Microscope.
The stalks of these compound vorticellse are con-
tracted together, so that a large mass, expanding
over the whole field of the Microscope, suddenly
disappears, and, " like the baseless fabric of a vision,
leave not a wrack behind." A little patience,
however, and the fearful creatures will once more
be seen to expand themselves in all their beauty.
66 A HALF-HOUR WITH THE
The mouth of their little cup is surrounded by cilia,
which are in constant movement j and when ex-
amined minutely, they will be found to possess two
apertures, through one of which currents of water
pass into the body, and from the other pass out.
Not unfrequently the cup breaks off its stalk. It
then contracts its mouth, and proceeds to roll about
free in the water. Many other curious changes in
form and condition have been observed in these
wonderful bell-shaped animalcules.
If, now, we go to a very dirty pond indeed, into
which cesspools are emptied, and dead dogs and
cats are thrown, we shall find abundant employ-
ment for our Microscope in the beautiful forms of
animalcules which are placed by the Creator in
these positions to clear away the dirt and filth, and
prevent its destroying the life of higher animals.
In such waters, amongst a host of minor forms, we
are almost sure to meet with the magnificent Para-
mcecium Aurelia, figured at 39, plate 2. He moves
about the water a king amongst the smaller prey,
on whom he feeds without ceasing. He is of an
oblong form, covered all over with cilia, and very
rapid and active in his movements, as able to dart
backwards as forwards, and turning round with the
greatest facility. In his inside several spots are
observed. If a little indigo or carmine is intro-
duced into the water in which he lives, these spots
become coloured by his taking up these substances.
From this, Ehrenberg concluded that these spots
were stomachs, and as such spots are very common
amongst these animalcules, he called them many-
stomached (Polygastrica). There is, however,
reason to doubt the correctness of this conclusion
of the great microscopist, as, although these spots
exist in the body, they are not necessarily stomachs.
They are, in fact, empty spaces, or vacuoles in the
MICEOSCOPE AT THE ?OND-SIDE, 67
interior of the little fleshy lump of which the ani-
mal is composed. They are found in the vorticella,
and in most of the true animalcules.
All animalcules have been called infusory, be-
cause they seem so abundant in many kinds of
vegetable infusions. Ehrenberg divided them into
Polygastric and RotifeTous. The last are also called
wheel-animalcules, as, when looked at through the
Microscope, they appear to be supplied with little
wheels on the upper part of their body. The most
common form of these creatures is the Rotifer
vulgaris, represented at figure 41, plate 2. The
branches or leaves of any of our common water-
plants can scarcely be examined without some of
those pretty little creatures being found nestling
among them. The structure of these creatures is
highly complicated, and the family to which it
belongs is far removed from the poly gastric ani-
malcules with which it is associated by Ehrenberg.
On examination, the wheels will be found to
consist of two extended lobes, the edges of which
are covered with cilia. These cilia are in a con-
stant state of movement, and produce the appear-
ance of wheels moving on an axis. Between the
wheels is the entrance to the mouth, which, in
many species of wheel-animalcules, is furnished with
a strong pair of jaws. This leads to an oesophagus,
a stomach, and an intestinal tube. Two little spots
on the neck seem to indicate the existence of eyes ;
whilst a projecting organ, believed to be analogous
to the antennae, or feelers of insects, is seen
directly below them. The tail is finished off with
a pair of little nippers, by which the creature has
the power of attaching itself to objects. When
moving, its whole body is extended, but it has the
power of drawing itself up like a telescope in its
case, and appearing almost round.
P 2
68 A HALF-HOUR WITH THE
The wheel-animalcules abound in our ponds and
rivers, and sometimes occur in great numbers in
the aquarium. The common wheel-animalcule,
Rotifer vulgaris, is most frequently found in lead
gutters and the drinking-fountains used for birds.
If a little of the deposit which usually accumu-
lates in the former is placed in a test-tube with
water, and exposed to the light, in a short time the
rotifers will be found swimming about in great
numbers, and may be transferred to a live-box by
means of a dipping-tube : if allowed to dry, they
can be afterwards revived by adding a little water.
Several of the wheel-animalcules are fixed, forming
on the outside of their bodies a little case or tube
in which they dwelh These forms are beautifully
seen when illuminated by the spot lens.
MICROSCOPE AT THE SEA-SIDF. 69
CHAPTER V.
A HALF-HOUB WITH THE MICEOSCOPE
AT THE SEA-SIDE.
ON a visit to the sea-side, the Microscope is an
essential instrument to all who would wish to
study the wonders of the ocean. It is a curious
fact, that the few grains of common salt in the
gallon of sea-water seem to determine the exist-
ence of thousands of plants and animals. We shall
therefore find living in the sea-water, plants and
animals belonging to the same families as those
in fresh water, but belonging to entirely different
species.
The sea-weeds present strikingly different forms.
Although many of them are microsopic, and belong
to the families of Diatomacece and Confervacece, all
the larger forms present interesting objects for
examination in the structure of their fruit-bearing
organs. No better subject for the latter purpose
can be procured than the common bladder-wrack,
which is so abundant on all our shores. If a frond
of this fucus is examined, there will be found at
certain parts a swollen mass, dotted over with
round yellowish bodies. If one of these is taken
and carefully pressed between two pieces of glass,
it will present the spores surrounded with hairs
of the most delicate and various structure. Some of
the spores are divided into four parts, and on this
account are called tetraspores. These are seen at
d, figure 111, plate 4. The bladder-wrack is fre-
quently covered with minute parasites ; one of the
most common of these is Polysiphonia fastigialcl,
70 A HALF-HOUR WITH THE
which is represented at figure 111, plate 4. As
seen in the drawing, this little plant is branched,
and the stems present a series of flattened cells.
On the branches are placed the fruit-bearing
organs, in the form of little capsules, seen at a.
These capsules contain tetraspores (d). At the
ends of the branches are organs of another kind,
representing the stamens, and which are called
antheridia. These are seen at e in the same figure.
The sea-weeds present a great variety in the form
of these organs, and may be easily preserved for
investigation in small glasses of sea-water.
The animal structures of the sea-water must
now, however, claim our attention. Amongst the
lowest form of animal life are the sponges. They
are frequently cast on the shore with sea-weeds,
and afford interesting objects for the Microscope.
They are composed of animal matter, which lies
upon a structure of horny, calcareous, or sili-
ceous matter. The common sponge which is used
for domestic purposes may be taken as a type of the
whole group. If a thin section of the common
sponge is made with a pair of sharp scissors and
placed under a low power, it will be seen to be
composed of a network of horny matter, repre-
sented in figure 140, plate 5. If now we take one
of the common forms from our own sea-shore, we
shall find that the network is composed of sili-
ceous spicules lying one over the other, as repre-
sented in figure 141 of plate 5. If one of these
spicules is examined (a) and compared with a
spicule from another sponge, it will be found to
differ in form and size ; and the species of sponges
can actually be made out by the shape of their
spicules. Some of our British sponges have cal-
careous spicules. This is the case with Grantia
ciliata. There is a little boring sponge, called
MICROSCOPE AT THE SEA-SIDE. 71
Cliona, found in the shells of old oysters, which
has its spicules pin-shaped, as seen at figure 142.
The fresh-water sponge has very peculiar-shaped
spicula, and is represented at figure 143. In some
the siliceous bodies are round, with projections,
as in Tetliea, seen in the drawing, figure 145.
Sometimes the spicula assume a stellate form,
and are even branched, as in the spicula of an
unknown sponge given at figure 144.
Amongst the lowest forms of animal life, none
are more interesting to the microscopic observer
than those belonging to the family of Foramini-
fera (Hole-bearers). They are thus called on
account of the minute holes which cover their
shells. If we suppose a creature as simple in
structure as the amoeba, or sun animalcule, of which
we have previously spoken, and which are figured
in 16 and 17, plate 1, with the power of forming
a little calcareous shell, we should have a foramini-
fer. Some of these shells have the form of a
nautilus, and when first observed they were sup-
posed to belong to this group of shell-fishes. In
form they certainly resemble the higher forms of
mollusca, as may be observed in figures 21 and 24,
in plate 1. Sometimes, however, they are elon-
gated or cone-shaped, as in figure 25. Other forms
are seen in figures 20 and 22. They may often
be found alive -at the sea-side, nestling in the roots
of the gfgantic tayles which are so often thrown
on the shore after a storm. If the roots of these
plants (Laminarice) are washed, and the deposit
examined carefully, the foraniinifera will be seen
at the bottom of the vessel, and may be picked
out one by one. When this is done, they will be
found to have the power of protruding through the
little holes in their shells their soft bodies, in the
form of long tentacles, as seen at figure 24, in the
? 2 A HALF-HOUR WITH THE
first plate. With these they seem to have the
power of moving, as well as of taking up the
matters by which they are nourished. The shells
of these creatures are not so small but they may
be seen with the naked eye, and they need only a
low power to observe all their structure. They are
found at great depths in the ocean, and have been
brought up by the dredge from the deepest parts of
the Atlantic. They are very abundant in some
rocks, especially in the chalk : they may be ob-
tained from the latter substance by rubbing a piece
of chalk with a brush in water. The water must
be first decanted from the coarser particles of chalk,
and in subsequent deposits the foraminifera will be
found. They may be obtained from dry sand in
which they are contained, by throwing the sand
into water, when the sand will si'nk and the
foraminifera will swim on the surface, and may be
skimmed off. They are best examined as opaque
objects.
The family of polyps will next command atten-
tion. One of the most simple forms of this family
is found in ponds and rivers, and is called the
fresh-water polyp or hydra. It is figured at 146,
plate 5. It may be easily observed, adhering to
plants, with the naked eye, and needs only a low
power with transmitted light to observe it accu-
rately. Its body is cup-shaped, surmounted with
eight long tentacles, which it has the power of re-
tracting. It produces young ones by the process of
budding, and the buds may be often seen protrud-
ing from the side of their parents. It is very
tenacious of life, and may be cut into several pieces,
and each part will grow into a new hydra. These,
with many other polyps and the jelly-fish, have their
flesh filled with little hair-like bodies, which, from
their property of stinging in some species, have
PLATE 6.
MICROSCOPE AT THE SEA-SIDE. 73
been called stinging hairs, as seen at a, figure 14G.
If we suppose several of these hydras placed in
little cups upon a common branch or stem, we
should have a Sertularia, or such an animal as is
represented at Figure 147, Plate 5. These polyps
are very common on all our sea-shores j and the
branches and cups are often cast up on the shore,
and regarded by the uninstructed as sea-weeds.
The branches and cups are called the polypidoms of
the animal, and assume a great variety of forms.
When the cups are fixed on ringed stalks, they
constitute the genus Campanularia, seen at figure
148, plate 5. These cups are often objects of great
beauty, as in those of Campanularia volubilis,
figured in 149. It is the polypidom which consti-
tutes the coral in the family of polyps, producing
the masses of carbonate of lime which sometimes
cover the bottom of the ocean and form reefs in the
sea. In one family of polyps, known as sea-fans
(Gforgoniai), which are calcareous, the fleshy mass
covering the horny polypidom contains spicula of
various forms, which are beautiful objects under the
Microscope. These spicula are seen at figure 150,
plate 5. The red coral of commerce is another
interesting form of these polypidoms. In some
families of these polyps, as in the campanularidse
and the corynidse, the young, before they arrive
at their mature stage, assume the forms of minute
medusae or jelly-fishes. These are exceedingly
beautiful objects for microscopic observation.
Another family of animals common enough in
the sea, are the star-fishes and sea-eggs (Echinoder-
mata). Although not themselves microscopic,
certain parts of their structure present very in-
teresting objects for examination. If a section is
made of one of the spines of the common echinus,
or sea- egg, it presents under a low power a beau-
74 A HALF-HOUR WITH THE
tifully radiated structure. This is seen at figure
151, plate 5. The suckers, also, of the same animal
present little rosettes, surrounded by a very delicate
hyaline disk, represented at figure 152. Upon the
surfaces of both star-fishes and sea-eggs will be
found little inoveable bodies which are called pedi-
cettarice. In the sea-egg they pos&ess three moveable
nipper-like limbs, whilst in the common star-fish
they present only two. These are represented at
figures 153 and 154, plate 5. A controversy has
been raised on the question as to whether these
bodies are parasitic animals, or part and parcel of
the structure of the creature on which they are
found. As they are so constantly present, they are
undoubtedly parts of the animal on which they are
found. The movements of the nippers are very
active, and they frequently lay hold of objects
which pass near them.
As common on the shore as the polypidoms of
the polyps, are the animal skeletons called, in some
parts of the country, sea-mats (Flustra foliaceci).
"When placed under a low power, and viewed by
reflected light, the sea-mat is composed of little
cavities or cells, seen at figure 162, plate 6. In
each one of these is seated a creature of much more
complicated organization than the polyps just ex-
amined. It has, it is true, a ring of tentacles ; but
if these are examined, the tentacles are found to be
covered with cilia, as seen at a, in figure 163,
plate 0. This family of creatures are called Polyzoa,
or Eryozoa, and form a group of animals which are
classed with the Mollusca, or shell-fish. Sometimes
these creatures attach themselves to sea- weeds,
oysters, stones, and other objects at the bottom of
the sea, forming a kind of cellular membranous
expansion. Such are the species of Lepralia,
figured at 155. Sometimes the cells are elongated
MICROSCOPE AT THE SEA-S1DF. 75
and elevated above the surface of the object on
which they are placed, as in the case of Bowerbankia,
seen at 156. A beautiful form of these creatures
is the shepherd's-purse coral (Notamia bursarici),
represented at figure 157. This creature belongs
to a group of the polyzoa, remarkable for possess-
ing little processes on the margins of their cells, in
shape resembling the bowls of tobacco-pipes, birds'
bills, and bristle-like organs. On examining them
with the Microscope, they present a very compli-
cated organization. The birds' bills possess two
jaw-like processes, which open and shut like a bird's
beak, and from this fact they have been called avicu-
laria, or bird's-head processes (a). The tobacco-pipe
form in Notamia is peculiar to that genus. In
other species, as in Eugula, avicularia, seen in
figure 158, these creatures possess not only the
bird's-head process, but a second, consisting of a
long bristle or seta, attached by a joint to a process
below (a). These bodies are called vibracula, and
the bristle-like extremity is kept constantly in
action, and the form of avicularia is seen in Bugula
Murrayana, at figure 159. Both processes are seen
in Scrupularia scruposa, at figure 160. Few objects
are more curious under the Microscope than these
avicularia and vibracula in a state of action.
Whilst the function of the vibracula, seen at a,
figure 160, seems to be to sweep away objects
that would interfere with the life of the animal in
the cell, it has been suggested by some that the
avicularia secure by their jaws the food necessary for
its sustenance : it seems probable, however; that
they serve the purpose of a protective police. Of
the various forms which the cup itself assumes,
none are more interesting than those of the snake-
head zoophyte, shown at figure 161, plate 6, in
which it assumes the form of a snake's head, with
76 A HALF-HOUR WITH THE
the tentacula projecting like a many-parted tongue.
The polyzoa are also inhabitants of the fresh water.
Of these the most common form is the Plumatella
repens, figured at 163. The eggs of a fresh-water
species, Cristatella inuced<o, seen in figure 164, are
covered with projecting spines with double hooks
at their extremities, perhaps for the purpose of
catching hold of objects. Such eggs may be often
found upon portions of water-lily, bulrush, and
other aquatic plants which float about in our rivers,
lakes, and ponds.
Although but few of the shell-fish belonging to
the large class of mollusca are microscopic, yet the
structure of their shells can only be investigated
by the aid of the Microscope.
If any common shell be picked up on the sea-
shore, it will be found to possess a rough outside,
generally of a darker colour, and sometimes beauti-
fully ornamented, whilst on the inside it is smooth,
and frequently of a rose-colour. This inner smooth
layer is called the nacre of the shell ; and it is
from this substance that pearls are formed in the
interior of many shells. Both the outer and the
inner layers present different kinds of structure in
different species of shells. The outer layer can be
well examined in the shell of the mollusc called the
Pinna. The outer layer in this shell projects be-
yond the inner, and may be easily submitted to
examination by reflected light under a low power,
when it will exhibit the appearance represented at
figure 166, plate 6. The external surface presents
the appearance of hexagonal cellular tissue. If a
portion of the shell is ground down, so as to form
a very thin layer, it may be examined with trans-
mitted light, and its hexagonal structure will be
much more apparent. If a portion be examined
lengthwise, it will be seen that the hexagons result
MICROSCOPE AT THE SEA-SIDE. 77
from the shell being composed of a series of hex-
agonal prisms, as seen in the view of a longitudinal
section given at figure 166, plate 6.
All bivalve shells partake, more or less, of this
character ; and if a portion of the outer coating of
the shell of the oyster be examined, it will be
found to present a general resemblance to that of
the shell of the pinna, as seen at figure 167. In
many shells the inner layer is almost structureless,
but in those cases where the smooth white appear-
ance is presented which is called mother-of-pearl, it
consists of a series of waved laminae lying irre-
gularly one on the top of the other ; represented at
figure 169. In other shells this membranous in-
ternal layer is traversed by minute tubes, as is seen
in the genus Anomia, seen at figure 168. This
structure has been considered clue to the natural
form of the shell ; but late investigations lead to
the conclusion that these tubules are the borings of
some parasitic animal.
The shells of the Crustacea also present a series
of very interesting structural differences. The shell
of the common prawn, when mounted in Canada
balsam, or examined in water or glycerine, presents
a series of bodies looking like nucleated cells.
These are seen in figure 170, plate 6. Many
shells present this appearance, and it was at one
time supposed to indicate clearly that the shell
originates in cell-growth as well as other parts of
the structure of an animal. It has been, however,
recently shown, that such appearances as that pre-
sented by the prawn-shell may be produced by the
crystallization of inorganic salts in contact with
organic substances in solution, independent of a
living organism.
Surprising as it may seem to some persons, the
teeth of mollusca afford beautiful objects for mi-
78 A HALF-HOUR WITH THE
croscopic examination. All that is necessary to
examine these organs is, to take the palate, or
tongue, as it is called, of any of our common mol-
luscs, and to stretch it on a glass slide, when it may
be seen by transmitted or reflected light. In the
common whelk, the teeth are placed in rows, and
are composed of a broad base with four projecting
points, the two outer of which are larger than
the inner, as seen in figure 171, plate 6. In the
limpet, the teeth present four projections, which
are all of the same size ; seen in figure 172. In
the common periwinkle another kind of arrange-
ment is observed, and is figured at 173.
When sea-side specimens have been observed and
put up, the fresh-water mollusca may be next
investigated. Here other forms will be observed.
The species of the genus Limneus are found
in every pond, and kept in every aquarium.
The tongues of these creatures, represented at
figure 174, will give a lively idea of the nature
of the scavengering processes they carry on .
The scales of fishes are interesting microscopic
objects. The structure of these organs indicates
the family of fishes to. which they belong. It is in
this way that a single scale found in a rock will
throw a light on the nature of the fishes which
inhabited the seas or rivers from which the rock
was deposited.
Fishes' scales have been called ganoid, placoid,
cycloid, and ctenoid, according to the families to
\vhich they belong. The sturgeon has ganoid
scales. They are shiny, and have a structure
like bone, and are represented at figure 175,
plate 6.
The sharks, rays, and skates have placoid scales.
They are frequently terminated with a prickle, as
in the scales of the skate ; seen at; figure 1 76.
MICROSCOPE AT THE SEA-SIDE. < W
This structure resembles the tubular structure in
the teeth of the higher animals.
Fish-scales are frequently permeated with minute
tubes, drawn in figure 177, plate 6. These appear-
to be the work of some minute parasite, such as
that producing the tubules in shells, and which has
hitherto evaded the scrutinizing investigation of
the microscopic observer.
The fishes of the earlier rocks belong to the
ganoid and placoid groups. The great majority of
recent fishes belong to the remaining groups. The
common sole affords an instance of the ctenoid, or
comb-like scale, seen at figure 178.
The cycloid, or circular scales, are found in such
fish as the whiting, and represented at figure 179.
It is not uncommon to find in these scales cal-
careous particles, shown at a. In the sprat the
cycloid scale assumes a form almost as broad as it
is long, and is seen in figure 180.
The examination of these hard structures in the
marine creatures is a good preparation for the
further study of those hard parts in the higher
animals to which the name of bone and ivory i&
given. Such things may, however, be procured in
the house ; and when the rain is falling, the sea-
side forsaken, or the country miserable -looking, we
can still enjoy the long winter evenings with our
Microscope in the house.
80 A HALF HOUR WITH THE
CHAPTER VI.
A HALF-HOUR WITH THE MICROSCOPE
IN-DOORS.
FOB amusement and instruction with the Micro-
scope, we need scarcely stir out of our rooms. The
very hairs on our head may be made objects of
interesting investigation, and especially if we com-
pare them with the hairs of other animals, and the
appendages generally of the skin. The fine outer
coating of the skin is composed of minute scales,
which are flattened cells, and may be easily ob-
served by scraping a portion of the skin on to
a glass slide with a drop of water on it. The nails,
the hairs, and other appendages of the skin, are
composed of the same kind of scales, or cells.
These cells are developed in little pits, or follicles,
from which the hair is projected, as it were, by
their growth from below. Under a low power the
cells of the human hair cannot be observed. It pre-
sents, however, a well-marked distinction between
the outside, or cortical layer, and the interior, or
pulp. The latter, by a high power, especially if
the hair has been first submitted to the action of
sulphuric acid, will be found to contain cells more or
less spherical, whilst the former contains cells more
or less flattened. These project a little beyond the
edge of the hair, so that its sides are not quite
smooth, as seen at figure 184 in plate 7. By
placing a hair between two pieces of cork, fine
transverse sections of it may be made by means of
a sharp razor. If these are put under the Micro-
London. "Robert Hardwicke, 1860.
MICROSCOPE IN-DOORS, 81
scope, the pulpy portions will present a dark ap-
pearance in the centre, as seen at a. The hairs of
animals offer a great variety in the disposition of
the cells of which they are composed. The hairs
of the mouse present a series of dark partitions
running across the hair between the cells. In the
younger hairs, these partitions are single, as repre-
sented at a in figure 185, plate 7 ; whilst in the
older ones they appear double, as seen at b. The
hairs from the ear of the mouse present these dark
partitions very distinctly, shown at d. Such hairs
stand intermediate between true hair, a section of
which is seen at c, and wool. A -piece of flannel or
blanket will afford a good illustration of the latter.
This is figured at 235 in the 8th plate. In this
case it will be seen that the scales, or cells, of the
cortical part, project beyond the surface, and render
the wool rough. This roughness of the outside is
supposed to render such hairs fitted to be used in
the process of felting ; the rough sides of the hairs
adhering together. The chemical composition of
the hair has also something to do with this pro-
cess. Human and other smooth hairs, will not
felt.
The fibres of plants used in weaving may be
conveniently compared with hairs derived from the
animal kingdom. The woody fibre of the flax may
be obtained from a linen handkerchief. A linen
fibre is represented at 6 in figure 234, plate 8.
The apparent knots in the fibre arise from injury
in the uses to which the fabric has been applied.
The original fibres have no such fractures, as shown
at a, and are perfectly smooth. So are the fibres
of silk, represented at figure 236. Cotton-wool ia
produced from the inner surface of the pod, or fruit
of the cotton-plant, and is figured at figure 237. It
becomes twisted during its growth, and although
82 A HALF-HOUR WITH THE
not so strong as linen or silk, its irregular surfaces
permit its being spun into a strong yarn, from
which all cotton fabrics are made. The young
microscopist should make himself acquainted with
the forms of these various fibres ; as, from their
being so constantly present in rooms where the
Microscope is used, and occasionally employed in
cleaning the apparatus, they often present them-
selves as foreign substances, among other objects
that are being examined.
It is also interesting, and sometimes of import-
ance, to be able to ascertain of what material a
fabric may be composed. Thus by means of the
Microscope, and that alone, we know certainly that
the cere-cloths in which Egyptian mummies ara
wrapped is a linen fabric, whilst the similar invest-
ment of Peruvian mummies is cotton. The hair of
the bat, represented at figure 186, plate 7, presents a
singular instance of the projection of the scales, or
cells, in a regular form. Hairs are not often perfectly
round ; — in the peccary they are oval, as seen in
figure 187, plate 7. If a transverse section of this
hair is examined, it will be found that the cortical
substance projects completely into the pulpy part
of the hair in several places, so as to break up the
pulp into several separate sections.
In some cases it is not easy to distinguish
between outside and inside structure, as seen in
the hair of the musk-deer, in which the whole is
found to consist of a mass of hexagonal cellular
tissue, similar to that seen in the pith of plants.
This hair is shown in plate 7, figure 188.
Insects are frequently covered with hairs, espe-
cially in their larva, or caterpillar state. These
hairs when stiff and sharp, penetrate the skin,
and produce irritation there. This is the case with
the large tiger caterpillar. The hairs of this cater-
MICROSCOPE IN-DOORS. 83
pillar are furnished with a series of barbs, which,
when they once penetrate the skin, are not easily
removed, as seen in figure 189, plate 7.
Spiders are frequently covered with hairs, some
of which are branched, as at a in figure 190;
others present a spiral appearance, seen at b ;
whilst, again, others offer a series of small bristle-
like hairs running down each side of the primitive
hair, which will be seen at c.
Many of the Crustacea have hairs upon their
shells. Those upon the flabellum of the common
crab have minute bristles on one side of the parent
stalk, so as to form a little comb, with which to
brush off the impurities from its branchiae. This
structure is seen at figure 191 in plate 7. A live
crab from the aquarium may be watched for the
purpose of observing these cleanly movements.
The study of the uses of the epidermal ap-
pendages is one full of interest, as in no one
set of structures do we find a greater variety of
adaptations of a common plan to the wants of the
creatures in which they ,are found. The feathers
of birds belong to the same type of structure as
the hairs of animals. If the pinnae of a common
goose-quill, used for a pen, are examined, the
pinnules will be found to be covered with minute
hooks, drawn in figures 192 and 193, plate 7. These
hooks on the upper surface are so arranged that they
catch the nearly plain and slightly toothed pinnules
on the lower side.
The down from the feathers of the swan, with
which pillows and beds are stuffed, is also a beau-
tiful object, and its microscopic structure will at
once reveal the cause of its lightness, softness, and
warmth. This is seen at figure 194, in the 7th
plate.
Amongst the creatures which domesticate with
G 2
84 A HALF HOUR WITH THE
us are certain insects which are more frequentiv
discovered than acknowledged. However dis-
agreeable their presence may be, they become
interesting objects for microscopic investigations,
and are not less calculated to excite our admira-
tion than creatures more ceremoniously treated.
"We first call attention to the common flea (Pulex
irritans). This beautiful insect belongs to a large
family, each species of which has its peculiar habitat
in the epidermal appendages of some of the higher
animals. The head of the human flea may be taken
as the type of the family. This is represented with
great accuracy at figure 19o, in plate 7. It is
furnished with antennae, mandibles, and a pair of
lancet-shaped jaws, with which it makes little
wounds in the skin, and into which it pours the
irritating secretion which renders its bite a source
of annoyance. Its eye, large hind legs, and orna-
mental saddle on its back, are all deserving of
attention.
Let us now seek another too common inhabitant
of London houses, the bed-bug (Gimex lectulwiua),
and, having decapitated 'him, submit his head to a
low power. He, too, is a biting creature ; and you
will observe, as drawn in figure 19G, that his jaws
are finer than those of the flea, and are like a pair
of excessively fine sharp hairs ; they are inclosed in
a sheath, from whence they are projected when
used. In the same sheath is the tongue, which
performs the double office of depositing in the
wound an acrid and irritating secretion and suck-
ing up the blood of its victim. The antennae and
eyes of the bug are also worthy of examination.
From the latter will be found projecting minute
hairs.
A still more despised animal may now be sought
(PedicuZus). It also belongs to a large family, and
MICROSCOPE 1K-DOOBS. 85
each mammal and bird seems to be attended with
its peculiar louse. Two species are found in dirty
and diseased conditions of the human body. Dis-
gusting as connected with want of cleanliness, they
are, nevertheless, perfectly harmless. The head and
mouth, drawn in figure 198, indicate that these
creatures are adapted to live on the secretions of
the skin. The above animals all belong to the
much larger group of creatures adapted to live as
parasites upon other animals.
The head of the common gnat, figured at 199,
in plate 7, may be now examined for the sake of
comparison. In this creature, the eye of the insect
may be studied. It is what is called a compound
eye, and is composed of innumerable small lenses ;
each one of which is connected with a twig of the
optic nerve, and capable of receiving impressions
from external objects. The little lenses terminate
on the convex surface of the eye, presenting an
immense number of hexagonal facets. These are
seen at figure 210, plate 7. In the common
house-fly, there are said to be 4,000 of these facets;
and in the cabbage-butterfly 17,000. The antennae
of the gnat are very beautiful ; and, in fact, these
organs in insects afford an endless variety of forms.
At their base, in the gnat, is seen a round process
on which these are seated, and it has been supposed
that they are organs of hearing. Whether they
are organs of hearing or not, it is very certain that
they are organs of touch, and the creature is very
susceptible of the slightest stimulus applied to
them.
The head of the honey-bee may be now examined ;
and if a careful dissection is made of its mouth, a
marvellous apparatus is unfolded to view, which is
exhibited in figure 201, plate 7, At the base is
seated the so-called mentum, and on each side aro
86 A HALF-HOUR WITH THE
placed the mandibles ; above these, and longer, are
the maxillce, and on each side of the prolonged
central organ, called the tongue, are placed the labial
palpi. The tongue can be retracted between the
palpi as into a sheath. It is marked by a series of
annular divisions, and, by a high power, will be
seen to be covered over with hairs. This is the
organ by means of which the bee " gathers honey
all the day."
Whilst examining the bee, its sting may be
taken out and placed under a low power, when it
will be found to present the appearance of a pair
of spears set with recurved barbs, which run part
of the way down one side of each half of the sting.
This is seen in the 7th plate, figure 200. Each of
these spears is grooved on the opposite side, the
two, when united, forming a canal, down which are
poured the contents of the poison-bag, producing
the painful effects of wounds from these instru-
ments.
To return to the head and mouth of insects : —
The tongue of the bee may now be compared with
the same organ in the butterflies, which in them
assumes the form of a proboscis, and is called the
hausteHum, seen at figure 203, plate 7. This
instrument is coiled up when the insect is at rest,
and is the organ by means of which the creature
sucks up its nutriment from the flower. It has a
series of lines running across it.
If the head of the common blowfly be now
examined, it will be seen that the tongue, instead
of being elongated as in the latter instances, is
expanded laterally. This is represented in figure
202, plate 7. It is a very beautiful object, and
when viewed by transmitted light, a series of spiral
bands are observed to wind across each half of the
tongue.
MICROSCOPE IN-DOORS. 87
The head of the common garden spider (Eperia
diadema) presents an interesting development of
the mandibles. These organs are in pairs ; each
mandible consists of two joints : one is small,
sharp, and hooked ; whilst the other is large and
short, and contains within it a bag, or poison-
gland ; so that when the creature seizes its prey,
the bag is pressed on, and a drop of the poison
exudes. This organ is represented in figure 204,
plate 7. This structure is similar to what is met
with in the poisonous serpents, where a poison-bag
is seated at the base of a tubular tooth.
The description above given is the generally
received one ; but Mr. John Blackwall, our greatest
authority on spiders, considers the use of the term
" mandibles " to parts entirely without the mouth
objectionable ; he has accordingly bestowed the
name of "falees" upon them. Some carefully-
conducted and interesting experiments of his on
their so-called poisonous secretion seem to throw
great doubts on the propriety of regarding them in
this light, and he has been led to consider that the
purposes of it may rather be to deaden pain and
still the struggles of a captured animal, as chloro-
form is given previous to and during operations on
human beings.
The head of the spider affords also a good
example of what are called simple eyes. Besides
the compound ones before mentioned, insects have
also these simple eyes — drawn at figure 208,
plate 7. They consist of a single lens, as seen at
a, and are placed in various positions in the heads
of spiders.
The skin of the common garden spider is covered
with hairs. These appear to surmount a series of
concentric plates, seen at figure 209, plate 7.
They vary in form in. different species of spider ;
88 A HALF- HOUR WITH THE
and the skin of all should be examined for tlio
purpose of observing these differences. The web
of the spider should also be examined. The cords
of these beautiful structures, which run from the
centre to the circumference of the web, are plain,
as seen at figure 214 ; whilst those which form
the concentric lines are beaded with drops of a
glutinous substance. It is by means of this adhe-
sive matter that the webs are held together. Nor
should the rnicroscopist neglect examining the
spinnarets of the spider, by which these beautiful
threads are elaborated.
The breathing organs of insects are well de-
serving attention. Their bodies are perforated at
the sides, and the openings thus formed, called
apirades, lead into tubes which are branched, and
are called trachece. These air-tubes are composed
of a delicate membrane, which is supported on a
series of delicate rings, which are easily traced into
the more minute branches. They are well seen in
the larvse of most of the lepidopterous insects, and
represented from a caterpillar in figure 222,
plate 8. The spiracle is not an open hole. In the
common house-fly, seen at figure 212, plate 7, and
the water-beetle (Dyticus], in figure 213, it is
covered over with irregular branched processes
from the sides of the opening. The object of this
obstruction is probably to prevent particles of dust,
and other foreign substances, from entering the air-
passages, and thus choking the animal.
The legs of insects \vill afford an almost un-
limited supply of objects for examination. The
spoilt specimens of a summer's capture may well
supply materials for a winter's examination. The
legs of insects are composed generally of five parts,
jointed together. The lowest of these is called the
tarsus, or foot. It is variously formed to adapt it
m
London : "Robert Eardwi&kB, i860-.
MICROSCOPE IK-DOORS. 89
to the locomotive habits of the insect. In the
common fly it is terminated with a pair of disks,
which are covered with suckers, called pulvilli.
Those of the Empis, a species of fly, are drawn at
figure 205, plate 7. By means of these suckers the
animal is enabled to lay hold of smooth surfaces, and
thus to crawl up them. They also exude a glutinous
matter, which assists in this process. The same
kind of arrangement is observed in the common
bee, represented in figure 20G. The feet are also
covered with hairs, and are frequently suppMcd with
hooked joints, which assist the animals in laying
hold of rough objects where their suckers would be
of no use. In the spicier there are no suckers, but
the hooked joints and hairs enable the creature to
crawl with facility. These hooks are seen in the
foot of the spider in figure 207, plate 7. In the
Dyticus the fore leg is supplied with two large
suckers, which are seen in figure 218, plate 8,
besides a number of smaller ones, and a hook ;
whilst the foot of the middle leg is destitute of the
largo suckers, as seen at figure 219.
The legs of beetles are often covered with little
cushion-like bodies, which undoubtedly act as
suckers. These are seen at figures 215, 216, 217.
The three legs often differ very much from each other,
and probably perform modified functions, according
to their structure. This is well seen in the legs of
the whirligig-beetle (Gyrinus natator\ in which the
first leg, in figure 215, is very much elongated,
whilst the third is broad and short, as at figure 217.
and adapted for swimming, from its oar-like form.
The second leg, seen at figure 216, is intermediate
in form and size.
As a contrast to these legs, adapted for the
varied functions of the perfect insect, the leg of
any common caterpillar may be examined ; when it
90 A HALF- HOUR WITH THE
will be found to consist, at its extremity, of a little
sac surmounted with hooks. These hooks are
represented in figure 223, plate 8.
The wings of insects, too, are beautiful objects \
easily investigated by a low power. The nerves
which run through them are supplied with tracheae,
and they thus become organs of respiration. The
under wing of the bee is supplied with a series of
hooks, seen at figure 211, plate 7, which slide on
a thickened nerve on the upper wing, marked a,
and keep the wings steady during flight.
The lepidopterous insects, including the butter-
flies and moths, have got their name from the scales
on their wings. These scales assume a wonderful
variety of form, and claim a large amount of atten-
tion from the microscopic observer, and cannot be
neglected by the entomologist.
The little blue argus butterfly has scales in the
shape of a battledore, drawn at figure 225, plate 8,
the handle being the part attached to the wing.
All the scales have handles of this sort, whatever
be their shape. At figure 226, a scale of ordinary
shape is represented. Sometimes the scale is broad
at the base, and pointed at top. In the meadow-
brown butterfly, the point is surmounted with little
clubbed projections, drawn at figure 227. Scales
are found on other insects besides moths and butter-
flies : thus they are found on the common gnat.
These are shown at figure 228. Besides their
curious forms, the scales are marked with lines
which are exceedingly delicate, and require the
highest powers of the Microscope to bring them
out. Some of the scales are thus used as tests for
the powers of the Microscope.
Just as we have seen in the tongues and legs of
insects, the same parts expanded or compressed
according to the wants of the animal, so we find the
MICROSCOPE IN-DOORS. 91
scales assuming various forms. The scales stand in
exactly the same relation to the hairs in insects,
that the scales of fishes and reptiles do to the
feathers of birds and the hairs of mammals. Hair-
like scales are therefore not uncommon. At figures
229 and 230, such scales are represented, and may
be found on the common clothes-moth.
The young microscopist, for whom our book is
written, and with which we hope to make him
dissatisfied, in order to facilitate his progress in
natural history inquiries, will not spend much time
in making dissections. Should he wish to do so, he
well find the structure of insects full of interest.
He has only to open a cockroach to see how
curiously their digestive apparatus is constructed.
This insect has a gizzard, and at the upper part it
is beset with six conical teeth, as seen at #, in
figure 220, plate 8; these teeth, working together,
reduce its food to a pultaceous mass previous to
digestion. When cut open, their position and re-
lations can be easily seen, as figured at b. The
gizzard of the cricket is also supplied with teeth,
seen at a, figure 221 ; it has three longitudinal
series of teeth, and each row in each series contains
seven teeth. The family of insects to which the
cricket belongs (Orthopt&ra) affords several other
instances of the same kind of structure in the
gizzard. It will be interesting to compare these
teeth of the insects with those of the mollusca and
the wheel animalcules.
We must satisfy ourselves with having shown
the student the way to cultivate a large field of
interesting and instructive phenomena in the insect
world, without going further into detail.
The tissues or textures of which animals are
built up or made may be easily procured in-doors.
We have spoken of the hard parts which form the
02 A HALF-HOUR WITH THE
outer skeleton of the lower animals, as the mol-
luscs, crabs, and fishes ; the internal skeleton of
the higher animals affords a not less interesting
field of research. If we take a piece of bone, and
having ground it so fine that we may examine it
with transmitted light under the Microscope, we
shall find it composed of a number of minute
insect-shaped cells, surrounding an open canal, as
seen at figure 232, plate 8. These cells, which are
called lacunas, and their little branches canaliculi,
are modifications, of the cells found in fishes' scales,
and figured at 175, plate 6.
These curiously-shaped cells differ in size and
form in the various classes of animals belonging to
the sub-kingdom Vertebrata, and thus a small por-
tion of a bone will frequently serve to indicate
whether an animal belonged to fishes, reptiles, birds,
or mammals. This is a matter of importance to
the geologist in determining the character of the
inhabitants of the earth at former periods of its
history. A section of whalebone is figured at 242,
plate 8.
The shells of eggs seems to be formed on the
same general principles as other hard parts, and the
tendency to the formation of cells with canaliculi
may be easily observed, as in the section of a com-
mon egg-shell, represented at figure 181, plate 6.
The young egg-shell should be examined, a section
of which is seen at 182, if the object is to study the
history of the development of the shell ; and this
may be compared on the one hand with the shells
of the Mollusca and the Crustacea,, and on the other
hand with those of the scales, teeth, and bones of
the vertebrate animals. Egg-shells present very
different appearances. The shell of the emu, for
instance, exhibits a series of dark triangular spots,
and is represented at figure 183, plate 6.
MICROSCOPE IN-DOORS. 03
As one of the hard parts of animals, the struc-
ture of cartilage is very interesting. A slice may
be obtained from the gristle of any young animal
Its structure is best seen in the mouse's ear, repre-
sented at figure 231, plate 8. No one who looks
at this object can but be struck with its resemblance
to vegetable tissue ; and it was this resemblance
which led to the application of the cell theory of
development, which had been made out in vegetable
structures, to those of animals.
Many of the soft parts of animal tissues afford
instructive objects under the Microscope. If the
tongue is scraped, and a drop of the saliva thus
procured placed under the Microscope, it will be
found to contain many flat, irregular, scale-like
bodies with a nucleus in the centre, such as are seen
at figure 4, plate 1. These scales are flattened cells,
and closely resemble those found on the surface of
the skin. Cells of a different kind line the air-
passages. If a snip be taken from inside the
nostril of a recently killed ox or sheep, it will be
found to be composed of cells which are fringed
with cilia at the top. These are seen at Figure 5,
Plate 1. These cilia are constantly moving, and
produce the motion of the mucus on the surface of
these passages which is essential to their healthy
action.
The blood of animals presents us with objects of
high interest. The human blood consists of a liquid
in which float two kinds of cells. They are discoid
bodies, from the three- thousandth to the three-
thousand-five -hundredth of an inch in diameter
(___!__ to 3-¥Vo)? and about a fourth of that size in
thickness. They are represented at figure 6,
plate 1. They are of two sorts — pale and red ; the
latter are rather smaller, but are by far the most
abundant. They present a little spot in the centre,
34 A HALF-HOUR WITH THE
which is called a nucleus, and this again another
little spot, which is called a nudeolus. The red
globules vary much in size and form in different
animals.- Thus, in birds, reptiles, and fishes, they
are oval instead of round ; and, mostly, in these
three classes much larger than in mammals. This
is especially the case in the batrachian reptiles, to
which the frog -and toad belong. Those from the
frog are shown at figure 8, plate 1. In the fowl,
shown at figure 7, and in the sole, seen at figure 9,
they are nearly twice as large as in man. In the
insects they are also frequently of large size, as in
the cockchafer, seen at figure 10.
The proof that blood-stains have been produced
by human blood on articles of dress and other
things, is frequently important in medico-legal in-
vestigations. Although it cannot be distinguished
from all other kinds of blood, it may be from some ;
and the Microscope has been employed as an adjunct
in such cases.
The structure of the skin, and other organs of
the body, are very interesting subjects for micro-
scopical investigation ; and volumes have been
written upon their diversified details. The struc-
ture of voluntary and involuntary muscular tissue
may be easily examined, especially the former, by
taking a portion of the flesh of any animal usually
eaten as food. The striated fibrillae of voluntary
muscle may be best seen in flesh cooked as food.
A muscle consists of bundles of fibres, and each of
these fibres consists of several fibrillse lying close
together. Each of these fibrils is seen to be crossed
with lines, represented in figure 233, plate 8.
These lines indicate the point of union of the
string of cells which form the ultimate parts of the
muscular tissue.
The structure of nervous tissue is also one of
MICROSCOPE 1N-DOORS. 95
high interest to the physiologist, bub it requires
the highest powers of the Microscope, and great
skill in manipulation, to make out.
96 A HALF-HOUR WITH
CHAPTER VII.
A HALF-HOUR WITH POLARIZED LIGHT.
WHAT is polarized light, and in what does it
differ from ordinary light 1 This question is often
asked, and, like many other questions in physical
and natural science, more easily asked than an-
swered.
To enable the young microscopist to form some
conception of the difference between common or
ordinary light and that known as polarized light,
it will be necessary to form some definite idea of
light itself.
Light, according to the modern theory, is pro-
duced by the vibrations or undulations of an ima-
ginary fluid called ether ; this is supposed to be a
rare and highly elastic fluid, occupying all space
and pervading all bodies : the vibrations of this
medium produce light, just as the vibrations of
air produce sound.
The length of these vibrations is inconceivably
minute, and their rapidity is represented by num-
bers which the human mind can scarcely compre-
hend. Upon the relative lengths of these vibra-
tions depend the differences of colour, red being
produced by the longest, and violet by the shortest
waves or vibrations.
For the production of the red ray, 37,640, and
for the violet ray 59,750 undulations in an inch
are requisite. In the production of the red ray
458 millions of millions, and in the violet ray
727 millions of millions of undulations take place
POLARIZED LIGHT. 97
in. a second of time. White light is produced
when the undulations are 44,440 in an inch, and
their number in a second of time amounts to 541
millions of millions. These vibrations are com-
municated to the retina and optic nerve, and from
thence to the brain. The rapidity with which
these undulations are communicated from their
source to the eye may be imagined when it is
stated that the light from the sun (a distance of
about 90 millions of miles) reaches us in 8 minutes
and 13 seconds; a railway train travelling at the
speed of 60 miles an hour would require 180 years
to accomplish the same distance. The light from
remotest nebula (according to Sir W. Herschel)
would, however, require 2,000,000 years to reach
the earth.
A ray of common light is supposed to have at
least two sets of vibrations ; viz., one vertical (or
up and down), and the other horizontal (or from
side to side).
These vibrations aro capable of being separated
either by reflection or by passing the ray through
certain transparent substances. The light is then
said to be polarized. The name is not, perhaps,
the best that could have been chosen, but as it
has been in use for many years, any alteration
would be attended with inconvenience.
The terms poles and polarity are usually em-
ployed to describe the contrary properties pos-
sessed by the opposite ends of bodies. Thus, we
have the north and south poles of a magnet, one
of which attracts what the other repels \ and when
it was found that the sides of a beam of light,
when reflected or transmitted under certain con-
ditions, possessed opposite properties, the ray
was said to be polarized from a fancied resem-
blance to the poles of a magnet or galvanic battery,
it
A HALF-HOUR WITH
An imaginary section of a beam
of common light is usually repre-
sented thus : and, of a beam
of polarized light .
In the following or
diagrams we shall represent the ordinary beam
by three, the ordinary polarized ray by two
parallel lines, and the extraordinary polarized ray
by a single line.
If a ray of light (Fig. 16) b impinges on a bundle
of glass plates, a, placed at the polarizing angle of
glass (56° 45') the ray is in part reflected and in
part transmitted, and both become polarized j c is
termed the ordinary, and d the extraordinary ray.
Fig. 16.
a, bundle of plates of thin glass ; 5, ray of ordinary light ;
<;, ray polarized by reflection ; d, ray polarized by refraction.
A polarized ray may be obtained by reflection
POLARIZED LIGHT. 99
from most polished surfaces, such as a mahogany
table, a tea-tray, a piece of japanned leather, &c.
During the earlier and later periods of the day,
the light reflected from that portion of the sky
opposite the sun is always polarized.
It will thus be seen that polarized light is of
common occurrence, but the unassisted eye is un-
able to detect it, although one-half of the ordinary
beam is lost. "We may here remark that the loss
of light caused by various optical contrivances is
not usually detected by the eye. This is well
illustrated by the Binocular Microscope. Let an
object be examined with the tube directly over
the prism with the prism in position ; if we re-
move the eye for an instant, and withdraw the
prism, no difference will be detected, although in
the latter case double the amount of light has
been transmitted through the tube.
This non-appreciation of an increase or diminu-
tion of light to the extent of 50 per cent, is per-
haps owing to the dilation and contraction of the
pupil of the eye.
If the reflected and refracted beams of polar-
ized light are thrown simultaneously on a white
ceiling and a white screen, the spectator will
observe two spots of light of equal intensity.
A polarized ray may be obtained —
1. By reflection.
2. „ simple refraction.
3. „ double refraction.
4. „ transmission through a plate of tour
maline or crystal of herapathite.
The diagram (fig. 16) on page 98 represents
the two first, c being the reflected, and d the
refracted ray.
The polarization of a ray of ordinary light by
H 2
100
A HALF-HOUR WITH
double refraction is shown in fig. 17 ; a is a rhom-
boidal crystal of Iceland spar. These crystals have
Fig. 17.
a, rhomb of Iceland spar ; b, ray of common light ; c, or-
dinary ray of polarized light ; d, extraordinary ray of
polarized light.
the property of splitting the impinging ray into two ;
thus, if a small hole is made in a card, and viewed
through a rhomb of Iceland spar, two discs of light
will be seen ; or, if a black line is drawn on a
piece of paper, two images of it will appear.
b is the ray of common light which becomes
divided as it passes through the crystal. These
rays are both polarized.
Certain varieties of tourmaline, when cut into
plates parallel to the axis of the crystal, possess
the property of polarizing common light. Fig. 18
represents such a plate.
Having seen how a polarized ray can be ob-
tained, the reader will ask, How am I to recognize
this condition of light ; fur you have already told
POLARIZED LIGHT.
101
me that it is not to be detected bv the unassisted
eye]
Fig., 18.
a, plate of tourmaline ; &, ray of common light ; c, ray of
polarized light.
In order to distinguish the difference between
ordinary light and that which has become polar-
ized, special means are required for that purpose.
It is an axiom that the medium capable of pro-
ducing polarized light is also capable of analyzing
it. Thus, if the reflected ray c (Fig. 16, page 9G)
is reflected on a mirror whose surface coincides
with that of the polarizer, the ray will be reflected
in the same manner as an ordinary ray j but if we
gradually revolve it until it stands at right angles
CL
of
d
Fig. 19.
a a, two slices of tourmaline -with angles coincident ;
I, beam of common light ; c, polarized ray ; d, ditto trans-
mitted.
to the polarized, the ray is intercepted and de-
stroyed.
102
A HALF-HOUR WITH
Let a a' represent two plates of tourmaline
with their angles coincident, a is the polarizer and
of the analyzer ; with the plates in this position,
the polarized ray c passes through to d (Fig. 19).
Fig. 20.
6 &', two slices of tourmaline crossed ; 6, beam of common
light ; c, polarized ray stopped by &'.
If we now cross the plates, the ray c is no longer
transmitted. If the analyzer is now revolved
another 90°, the ray is again transmitted. Re-
volve it 90° more, the ray is stopped ; and, on the
completion of the circle, the ray again becomes
visible.
The following diagram illustrates the effect of
the various positions of the analyzer. At a the
ray is visible, at 6 invisible, at c visible, at d in-
POLARIZED LIGHT.
103
visible ; as the analyzer passes from a to 6, the
brightness of the image gradually diminishes ; from
6 to c the brightness increases. The positions
marked 1, 2, 3, 4, are called the neutral axes, only
half the amount of light being transmitted.
In order to analyze a polarized beam it is not
necessary that the analyzer should be of the same
material as the polarizer ; a reflected ray may be
examined by a tourmaline or crystal of Iceland
spar, and a refracted or transmitted ray can be
reflected from the surface of a mirror.
The student will have gathered from what wo
have stated in the preceding pages, that the effect
of an analyzer on a polarized ray is the alternate
transmission and stoppage of that ray. The most
gorgeous effects are, however, obtained when a
doubly refracting film is interposed between the
polarized ray and the analyzer, producing what is
termed " chromatic polarization."
This doubly refracting film receives the polar-
ized ray, and doubly refracts it ; in other words,
the series of undulations of which the ray is com-
posed on entering the film (sometimes called the
depolarizer) is broken into two systems within it,
forming the ordinary and extraordinary rays.
Fig. 22.
If a polarized ray is allowed to enter a film of
selenite, it becomes refracted, and forms two dis-
104
A HALF-HOUR WITH
tinct rays, a is a polarized ray, b the film of
selenite, " c is the extraordinary ray, d the ordi-
nary ray; but one of these rays is retarded. If
they are analyzed by a double-image prism, the
ordinary and extraordinary rays will again bo
divided into c d, c c and d d, d c ; and if the
original ray be passed through a circular aperture,
two coloured discs will be observed, the colour
depending upon the thickness of the selenite film. If
one disc is red, the other will be green, the colours
being complementary to each other.
When a plate of tourmaline or a Nichol's prism
is used, one of these rays is alternately suppressed.
If the analyzer is revolved, we shall find that
when the angles of the polarizer and analyzer
coincide, and supposing a red and green selenite is
used, the colours will appear in the following
order : —
Fig. 23.
At a the ray would be green, at b red, at c
green, at d red ; as the analyzer approached 1, the
colour fades ; when it reaches that position the
colour will disappear ; as it approaches 5, the red
increases in brilliancy until it reaches b, when it
will have reached its maximum brightness. In
the positions 2, 3, and 4, no colour will be found.
POLARIZED LIGHT. 105
Having endeavoured to describe as plainly as
possible the nature of polarized light, we will now
proceed to describe the methods usually adopted
for the purpose of applying polarized light to the
examination of microscopic objects.
The micro-polariscope usually consists of two
Nichol's prisms, mounted in appropriate fittings.
A Nichol's prism is composed of a crystal of Ice-
land spar. It will be remembered that a beam
of light, in passing through a rhomb of Iceland
spar, becomes doubly refracted, and both polarized
beams are visible ; for polarizing purposes this is
not by any means desirable, but the difficulty lias
been overcome in the following manner. A
rhomb is divided, as shown in fig. 24, and the two
halves cemented with Canada balsam ; the re-
fractive power of the film of balsam being different
to that of the spar, throws the second image out
of the field.
Fig. 24.
a, section of Nichol's prism ; &, film of balsam ; c, ray of
light; d, ditto passing out parallel to that of incident ray ;
€, refracted ray.
a represents a section of a Nichol's prism, b the
cementing film of Canada balsam, c a ray passing
into the prism, d the same passing out parallel
to the incident ray, e the refracted ray.
One of these prisms is mounted, as shown in
fig. 25, and is made to slide in the short tube
attached to the under side of the stage ; a is a
10G
A HALF-HOUR WITH
revolving collar connected with the tube into
which tho prism is fitted. By this contrivance
Fig. 25.
the surface of the prism can be placed at any
angle with the analyzer.
The prism used as the analyzer is sometimes
mounted in a brass cap, fitted over the eye-piece,
as in fig. 26 j or in an adapter screwed on to the
Fig. 26.
nose-piece of the Microscope into which the object-
glass is screwed.
By the first method the brightness of the field
and the definition of the object under examination
is not impaired, but the diameter of the field is
seriously diminished. By the latter plan the field
remains the same size, but a certain amount of
POLARIZED LIGHT.
107
definition is sacrificed (this, however, is scarcely
perceptible if the prism is of good quality).
Having fixed the polarizing apparatus to the Micro-
scope, we may now proceed to test its effects on
various objects. Some will be tinted with all the
colours of the spectrum, whilst others are either
not affected by the altered condition of the light,
or are merely black on a white ground, or white
on a black ground. The last-named objects are
best seen with a film of selenite placed beneath.
This is sometimes mounted between two ordinary
glass slides and placed below the object. The
selenite should, however, be mounted in such a
way that it can be revolved independently of the
object. This is done in several ways; the best
contrivance is perhaps the revolving selenite stage.
The following diagram represents one of the
simplest forms of revolving stage.
Fig. 27.
With these stages a set of selenites is usually
supplied ; these separately give the blue, purple,
and red, with their respective complementaries
orange, yellow, and green.
These discs generally have engraved upon
them the amount of the retardation of the
108 A HALF-HOUR WITH
undulations of white light thus — J, f , and -f- ;
and if these are placed so that their positive
axes (marked P A) coincide, they give the sum of
Fig. 28.
their combined retardations. If any be turned
until its P A is at 90° to the P A of the othei-s,
the lesser number is subtracted from the greater.
For instance, when the P A of the f is placed at
-right angles to the P A of the -£ the sum of the
difference is obtained = f; if the -J is now added
with its P A coinciding with the P A of the -»-, %
are obtained ; but if placed to coincide with the
P A of the f , | is the result.
Therefore by subtracting by 90°, or adding by
the P A, any number from J to L3, undulations
may be retarded which includes all the colours of
the spectrum.
To those who may wish to try the effect of
polarized light at a small cost, the following plan,
suggested by Professor Reinicke* will be found
useful.
Procure from twenty to twenty-five pieces of
thin covering glass flat and free from veins. The
size most convenient for the purpose is 18x12
mm. Fig. 29 represents the exact size. These are
to be fixed on a tube at an angle to the tube of
* Tfie Professor gays 50 to 60, but with that number the
loss of light is considerable.
POLARIZED LIGHT.
109-
35° 25". This tube may be made of cardboard, as
shown, in Fig. 30 (also the exact dimensions). The
Fig, 29.
width from a to I, and c to d = 12mm., that from
b to c, and d to e, equal to the length of the thin
gliLss, when placed at the proper angle. It will be
found convenient to cut the cardboard partially
9
Firj. 30.
through with a sharp knife from 6 to/, c to g, and
d to h ; near the bottom of the first division on
the other side paste a strip of card i ; carefully
paste the two edges of the card together; drop
110 A HALF-HOUR WITH
the pieces of glass into the tube, taking care that
the lower edge of the first piece rests on the card-
board lodge L When all the pieces are in posi-
tion a similar strip of card must be pasted on the
upper part of the opposite side of the tube. The
analyzer can of course be constructed the same
way. These square tubes can be fitted into cylin-
drical ones, and adapted to the fittings of the
Microscope.
Although with this form of polariscope the
young student will be able to examine many
objects by polarized light, the Nichol prisms are
far superior for the purpose, and most of the
opticians supply the polarizing apparatus for stu-
dents' Microscopes at a moderate cost (from 30s.
to 35s.).
Having now described the Micro-polariscope,
and the mode of using it, we will proceed to de-
scribe a few of those objects to which polarized
light may be effectively applied. Matter pos-
sessing a crystalline structure as a rule affords
the greatest variety of form and colour. The
following list of salts, &c., most of which are
easily procured, give a brilliant display of colour
when polarized : —
Chloride of Barium.*
Chlorate of Potash.*
Sulphate of Copper,*
NipVpl *
,, „ -LNlCKei.
„ „ Iron.*
„ „ Zinc.*
„ „ Lime.
Tartrate of Soda,*
Salicine.
lodo-sulphate of Quinine.
Asparagine.
POLARIZED LIGHT. Ill
Succinic acid.
Stearine.
Picrate of Aniline.
Chlorate of Cinchoniiie.
Borate of Soda.
Margarine.
Quinidine.
Santonine.
Sugar.
Uric acid.
Chromate of Potash.
Paraffine.
Platino-cyanide of Magnesium.
The beginner need not make use of a large
quantity of the material he is about to experiment
with, and the only apparatus he requires is a small
test-tube about 4 inches long and half an inch in
diameter. Fill about 1 inch of this with distilled
water (if the crystals are soluble in water), add
two or three crystals, and dissolve with heat if
necessary ; take up a small quantity with a dip-
ping tube and drop it on a perfectly clean slide or
cover. It is as well to prepare several slides,
allowing some to dry slowly, and others to be
evaporated over a spirit-lamp.
One of the most beautiful examples of crystalli-
zation is that of Salicine,and as merely recrystallizing
it from its solution will only result in disappoint-
ment, we will give explicit directions for the pro-
duction of the rosette form of crystals as in Fig. 2,
plate 9. A saturated solution of the alkaloid must
be prepared, a drop of the solution placed on a
glass cover, and held over a spirit-lamp until it
not only evaporates the water, but melts the re-
siduum. The cover must now be put in a cool
place, and protected from dust. If the cover is
112 A HALF-HOUR WITH
examined after the lapse of a short time, small
circular, semi-transparent spots will be found scat-
tered over the surface. Further crystallization
may be prevented by warming it and mounting in
Canada balsam or Dammar.
The iodo-sulphate of Quinine (Fig. 1, plato 9),
also requires special preparation.
These crystals were first prepared, and their
optical properties described by Dr. Herapath, of
Bristol. The following are his own directions for
making them : —
Mix 3 drachms of pure acetic acid with 1
drachm of alcohol ; add to these 6 drops of diluted
sulphuric acid (1 to 9).
One drop of this fluid is to be placed on a glass
slide, and the merest atom of quinine added,
time given for solution to take place; then, upon
the tip of a very fine glass rod, a very minute
drop of tincture of iodine is to be added. The
first effect is the production of the yellow or
cinnamon-brown coloured, composed of iodine and
quinine, which shows itself as a small circular
spot ; while the alcohol separates in little drops,
which, by a sort of repulsive movement, drive the
fluid away. After a time the acid liquid again
ilows over the spot, and the polarizing crystals of
iodo-sulphate of quinine are slowly produced with-
out the aid of heat.
Dr. Herapath also succeeded in producing these
crystals in large plates, which could be used in
place of tourmalines, and they are called artificial
tourmalines or Herapathite.
Santonine is an alkaloid prepared from the
so-called Semen Cynce, or worm seed. It is soluble
in alcohol, chloroform, and water. Each solvent
alters the character of crystal. With chloroform
the crystals assume a lace-like appearance; crystal-
POLARIZED LIGHT. 113
lized from water, they arrange themselves in tufts,
composed of small oblong plates, arranged round
a nucleus. Santonine may also be crystallized on
a hot slide, when crystals radiating from a centre
will be formed.
Asparagine, an alkaloid obtained from asparagus,
crystallizes in diamonds similar to the crystals of
Aspartic acid, shown in fig. 3, plate 9. This acic-
is obtained from asparagine, but is difficult to pro-
cure ; a specimen had therefore better be procured
from the dealers in microscopic objects.
Succinic acid is obtained by the distillation of
amber.
The preparation of slides of paraffine, stearine,
margarine, and wax offer no difficulties to the
beginner ; all that is necessary is to place a small
piece of the material on a warm slide ; then place
a thin cover over it, heat the slide until the
substance melts, press down the cover, continuing
the pressure until the slide is cold; or the slide
can be placed at once on the stage of the micro-
scope, and the gradual crystallization observed as
the slide becomes cold.
The medium in which a salt is dissolved affects
the form and arrangement of the crystals when
it is recrystallized. The media affording the best
results are gelatine, gum, and albumen.
The following method will enable the young
student to add many beautiful slides to his collec-
tion of polariscope objects. Dissolve, with heat, a
small piece of gelatine in the test-tube before de-
scribed, using a similar quantity of distilled water.
In another test-tube make a saturated solution
of the salt (sulphate of copper, for example), add a
few drops to the gelatine (mix thoroughly, but
avoid forming bubbles, stirring it with a glass rod
or piece of platinum wire) ; spread a drop on a
I
114 A HALF-HOUR WITH
glass cover, set aside in a cool place to dry ; this
will usually take about half an hour. If the
experiment has been successful, the crystals will
appear like fern fronds. (See fig. 4, plate 9.)
This figure will give some idea of the elegance of
form and beauty of colour ; but it is beyond the
skill of any artist to do justice to the beauty of
a good slide. The sulphates of nickel and iron are
also very good when crystallized out of gelatine.
"With chlorate of potash, a totally different form
of crystallization is produced, the crystals being
tabular and large. A very remarkable effect is
produced when a small quantity of a solution
of barium is added ; the barium will be found
to have crystallized in small moss-like tufts at
the angles. Chloride of barium mixed with
the gelatine solution assumes a dendritic form,
somewhat resembling sulphate of copper, but
polarizes differently. Gum arabic may be substi-
tuted for gelatine ; the modus operand* is, how-
ever, similar ; albumen (white of egg) requires to
be dried before it is added to the distilled water,
which must be only slightly warmed. The stu-
dent cannot do better than try the effect of the
different media ; some salts do better with gela-
tine, others with gum ; for example, he will be
able to produce more effective slides of tartrate of
soda with gum than gelatine.
Platino-cyanide of Magnesium must be prepared
without heat, as warmth alters the colour of the
crystals. "We have obtained the best results by
adding a few crystals to a drop of the gelatine solu-
tion previously placed on the slide, stirring them
with a stout bristle until dissolved, and then allow-
ing them to slowly recrystallize. These crystals,
like the iodo-sulphate of Quinine, will analyze a
polarized ray. They are best mounted in dammar.
POLARIZED LIGHT. 115
Very beautiful results may be obtained "by a
mixture of two or more salts. Mr. Davies, in the
Quarterly Microscopical Journal, Vol. II., N.S.,
gives the following directions for crystallizing the
double sulphate of copper and magnesia. Make
nearly a saturated solution of the two salts, place
a drop on a slide and dry rapidly, allowing the
slide to become hot enough to fuse the salt,
which will now appear as an amorphous film on
the slide. On slowly cooling, the salt will absorb
moisture from the surrounding air, and crystalli-
zation will commence from various points, assum-
ing the appearance of flowers. As soon as these
" flowers " are perfected the slide should be
slightly warmed and a little of pure Canada balsam
dropped upon it, and covered with the usual thin
glass cover.
Sugar requires a somewhat different treatment
to any of the crystals previously described, and
the tyro's first attempts will probably result in
disappointment. The best for the purpose is the
white " stone sugar." Dissolve this in water,
using enough to form a thick syrup ; spread a
drop on a cover, drying it quietly over a spirit-
lamp ; when dry place it in a damp cellar cr
cupboard. In the course of twenty-four hours
crystallization will have taken place. The cover
should now be mounted in balsam.
Passing from the inorganic to organic we pro-
ceed to give a few hints on the preparation of
specimens from vegetable and animal kingdoms.
The following are a few of the objects from the
former which the student will have little difficulty
in obtaining : —
Potato starch.
Tous les mois ditto.
i2
116 A HALF-HOUR WITH
Cotton fibre.
Hairs and scales from leaves.
Longitudinal sections of wood.
The first-named on our list can be very easily
procured by scraping a potato, and then shaking
the pulp in a test-tube with water, to which ;i
small quantity of soda has been added. The
starch will rapidly subside, and the fibrous matter,
&c., can be poured off. The washing should be
repeated until the starch is left perfectly pure.
Starch for polarizing purposes requires to be
mounted in Canada balsam. The hairs and scales
of plants require no preparation for mounting.
The scales of Eleagnus or ffippophce rhamnoides
(sea buckthorn) (Fig. 6, pi. 9), are easily procured,
and offer no difficulty to the young manipulator,
merely requiring to be detached from the cuticle
of the leaf with the point of a knife or lancet, and
afterwards transferred to a drop of water, to
which a minute quantity of gum has been pre-
viously added, when dry, mount in balsam.
The following list contains a few of the objects
from the animal kingdom : —
Fish scales.
Palates of Mollusca.
Hairs.
Quill.
Horn.
Whalebone.
Fish scales are so well known that no difficulty
can arise in obtaining specimens, with the excep-
tion of those from the eel, which do not occur on
the surface, but will be found imbedded in the
skin ; they may be obtained by picking the skit
with the point of a needle, previously scraping off
the mucus.
POLARIZED LIGHT. 117
The palates of mollusca, as polariscope objects,
are not as a rule very effective, that of the common
Whelk excepted.
Hairs are worthy of notice for polarizing pur-
poses, as they usually display a considerable amount
of colour. While horsehair and grey human hair
(Fig. 5, pi. 9) are perhaps the best for the student's
purpose.
The structure of Rhinoceros horn and whale-
bone is well displayed when polarized, but they
are difficult to prepare, and it would be better to
purchase them of the dealers in microscopic pre-
parations.
The mineral kingdom affords but few objects
that can be prepared by the amateur, although no
collection of polariscope objects would be com-
plete without one or more sections of agate and
chalcedony; and, like the objects previously
named, must be obtained from the dealer. The
young microscopist should, however, obtain from
some optician a piece of the so-called Brazilian
pebble (really transparent quartz), and break it
up into small fragments : many of these, when
mounted, display very beautiful coloured rings.
A few words may perhaps be necessary as to the
mode of procedure in mounting specimens of
crystal. We have in several instances directed
the solution to be placed on the cover ; our reason
for doing so is, in order to avoid the application
of any great degree of heat, and at the same time
using tolerably hard balsam.
The plan we adopt is as follows. Place a drop
of pure balsam on the centre of a slide, harden
over the lamp (it will be sufficiently so if the
nail slightly indents it when cold) ; now drop a
little turpentine on the prepared cover, holding it
as close as possible to the edge with the forceps,
118 A HALF-HOUK WITH POLARIZED LIGHT.
rewarm the slide, and apply the opposite edge of
the cover to the edge of the balsam, and allow
the cover to fall gradually down ; when the
glass disc is covered by the balsam, press care-
fully until all the superfluous balsam is squeezed
out.
We must now, however, draw our last half-hour
to a close. All we have attempted has been in the
"way of introduction. We have only described those
things which are most easily obtained,- and we have
sought rather to create a desire for further know-
ledge, than to impart an exhaustive amount of
information on any one subject.
Those who have properly apprehended our re-
marks will see that there is not a distinct science
of microscopic objects, but that these objects belong
to various departments of science, whose great facts
and principles must be studied from works devoted
to them. The Microscope is in fact an instrument
to assist the eyes in the investigation of the facts
of structure and function, wherever they may occur
in the great field of nature; and that inquirer
must have a very limited view of the nature of
science, who supposes either that the Microscope is
the only instrument of research, or that any in-
vestigation, where its aid reveals new facts, can be
successfully carried on without it.
APPENDIX.
BY THOMAS KETTERINGHAM.
THE PREPARATION AND MOUNTING OP
OBJECTS.
THE majority of objects exhibited by the Microscope require
some kind of preparation before they can be satisfactorily
shown, or their form and structure properly made out. To
convince the beginner of this, let him take the leg of any
insect, and, without previous preparation, place it under his
Microscope, and what does he see ? A dark opaque body,
fringed with hair, and exceedingly indistinct. But let him
view the same object prepared and permanently mounted,
and he will then regard it with delight. That beautiful limb,
rendered transparent by the process it has undergone, now
lies before him, rich in colour, wonderful in the delicate
articulation of its joints, exquisite in its finish, armed at
its extremities with two sharp claws equally serviceable for
progression or aggression, and furnished, in many instances,
with pads (pulvilli) (see plate 7, figures 205, 206), which
enable the insect to walk with ease and safety on the
smoothest surface. If the beginner has a true love for the
study of the Microscope, he will be glad of information
respecting the method pursued in dissecting and preserving
microscopic objects, nor will he rest satisfied until he has
acquired some knowledge of the art. We will briefly point
out a few of the advantages possessed by those who are able
to prepare specimens for themselves.
Objects well mounted will remain uninjured for years, and
will continue to retain their colour and structure in all their
original freshness.
They can be exhibited at all times to one's friends, and
may be studied with advantage whenever an opportunity
120 APPENDIX.
By the practice of dissection such a knowledge is gained
of the varied forms and internal organization of minute
creatures as can be obtained in no other way.
There are doubtless many who, possessing a small Micro-
scope, are unable by reason of their limited means to expend
money in the purchase of ready-prepared specimens. To
such, a few plain directions, if followed, will be of service,
and will enable them to prepare their own.
The materials necessary for the beginner are few, and not
expensive. In fact, the fewer the better ; for a multiplicity
is apt only to cause confusion. The following will be found
sufficient for all ordinary purposes, and may be obtained at
any optician's.
Bottle of new Canada balsam.
Bottle of gold-size.
Bottle of Brunswick black.
Spirits of turpentine — small quantity.
Spirits of wine — small quantity.
Solution of caustic potash (liquor potas$afy.
Ether— a small bottle.
Empty pomatum-pots, with covers, for holding objects
•while in pickle.
Half a dozen needles mounted in handles of camel-hair
brushes.
Pair of brass forceps.
Two small scalpels.
Pair of fine-pointed scissors.
Camel-hair pencils — half a dozen.
Slips of plate-glass, one inch by three inches — two dozen.
Thin glass covers, cut into squares and circles — half au
ounce.
We will suppose that the beginner, having purchased the
necessary materials, is about to make his first attempt. Let
him attend to the following advice, and he will escape many
failures.
He must bring to his work a mind cool and collected ;
hands clean and free from grease. Let him place everything
he may require close at hand, or within his reach. A stock
of clean slides and covers must always be ready for use. He
must keep his needles, scissors, and scalpels scrupulously
clean. An ingenious youth will readily construct for himself
a box to contain all his tools. Cleanliness is so essential to
success, that too much stress cannot be laid upon it. All
fluids should be filtered and kept in well-corked phials. A
bell-glass, which may be purchased for a few pence, will be
found exceedingly useful in covering an object when any delay
APPENDIX. 121
takes place in the mounting. For want of it, many specimens-
have been spoilt by the intrusion of particles of dust, soot,
and other foreign substances. Let the table on which the
operator is at work be steady, and placed in a good light,
and, if possible, in a room free from intrusion.
WINGS OF INSECTS. — Perhaps these are the easiest objects
upon. which the beginner can try his "'prentice hand." Here
little skill is required. Select a bee, or wasp, and with your
fine scissors sever the wing from its body ; wash it with a
camel-hair brush in some warm water, and place it between
two slips of glass, previously cleaned, which may be pressed
together by a letter-clip, or an American clothes- peg ; place
it in a warm corner for a few days ; when quite dry, remove
it from between the slides, and soak it for a short time in
spirits of turpentine. This fluid renders the object more
transparent, frees it from air-bubbles, and prepares the way
for a readier access of the balsam to the various portions of
its structure.
Having selected from your stock a clean slide of the re-
quisite size, and a thin glass cover somewhat larger than the-
object about to be mounted, hold them both up to the light,
when any slight impurities will appear, and may be speedily
removed by rubbing the surfaces of the glass with a fine
cambric handkerchief, or a piece of soft wash-leather.
Should, however, a speck or flaw in the glass itself be
found in the centre of the slide, at once reject it and choose
another. Remove the wing with a pair of forceps from the
turpentine, and place it in the exact centre of the slide :
this may be accomplished by cutting a stiff piece of card-
board, tin, or zinc, the size of the slide, and punching a
hole, the edge of which should be equally distant from each
end and each side ; lay the slide upon it, and place the
object in the circular space ; you will thus get it properly
centred.
Before dropping the balsam (which should have been
previously warmed) upon the specimen, place it under the
Microscope : you may possibly detect some foreign substance,
in the shape of a particle of soot or a fibre from your hand-
kerchief, in contact with it ; remove it with the point of a
needle. Take up a small quantity of the balsam on the end
of a small glass rod, and let it fall upon the object ; hold the
slide for a few minutes over the flame of a candle or spirit-
lamp at a distance sufficient to make it warm, but not hot ;
the balsam will gradually spread itself over and around the
object: should air-bubbles arise, they may be broken by
touching them with the point of a needle ; they will, how-
122 APPENDIX.
<ver, frequently dlspeise of themselves as the balsam dries.
The thin glass cover, being warmed, should DOW be placed
upon the object, and a slight pressure applied to get rid of
the superfluous balsam. Place the slide in some warm spot
to dry ; an oven will do very well, if the fire has been some
time removed and there is not sufficient heat to make the
balsam boil.
In a short time the balsam round the edges of the cover
will be hard enough to admit of the greater part being
scraped olF with a knife ; the remainder may be got rid of
by wiping the slide with a rag dipped in turpentine or ether.
The finishing touch consists in labelling the object with its
proper name. It will be found advantageous to place the
common name of the specimen at one end of the slide, and
its scientific name at the other.
Some persons prefer covering their slides with ornamental
paper, which may be obtained of almost any optician.
Others prefer the glass without any covering at all. In the
latter case the edges of the slide should be ground, the
round thin glass covers used, and the name scratched upon
the slide with a writing diamond. In the former, the edges .
of the slide, being covered with paper, need not be ground,
but square thin covers should be used instead of round ones,
and the name written with pen and ink in the square places
allotted at each end of the slide.
LEGS OP INSECTS (plate 7, figures 205, 206, 207 ; plate 8,
figures 215 to 219, 223, 224.— These require a little more
preparation than wings ; and as they possess some thick-
ness, and are mostly opaque, besides being of a hard, horny
character, they should be placed for a fortnight, or even
longer, in liquor potasses; this will soften the tissue and
dissolve the muscles and other matter contained within
them, so that by gently pressing the limb between two
slips of glass, the interior substance will gradually escape,
and may be removed by repeated washings. The squeezing
process, however, must be conducted gently, to prevent
any rupture : perhaps the best plan is to plunge the slips
of glass into a basin of clean water, when all impurities
oozing out from the pressure will sink to the bottom.
Should the leg not be sufficiently softened to be squeezed
quite flat, it must be again placed in the solution for
a longer period, until this result be obtained. On re-
moving it from the potash, it should be well washed with
a camel-hair pencil in clean \\ater, placed between two slips,
held together by an American clothes-peg \\ ith a good stiff
Al'l'ENDIX. 123
spriug. If placed in a warm corner, a few days will le
sufficient to dry it thoroughly : afterwards soak it in spirits
of turpentine ; the time of immersion to be regulated by the
opacity of the object.
The directions for mounting in balsam are precisely
the same as those given for the wings of insects. Care
should be taken not to heat the balsam too hot, as it will
invariably destroy delicate specimens by curling them up.
I n tough horny structures, such as the wing-cases of beetles,
&c., heat is sometimes an advantage, and there are a few
structures that show to advantage when the balsam has been
heated to a boiling pitch ; but for the majority of objects, a
gentle warmth is all that is required.
OVIPOSITORS AND STINGS (plate 7, figure 200) are more
difficult to prepare, and require some amount of dissection
before they can be properly displayed. To do this, some
degree of skill is necessary, and a knowledge of insect
anatomy, which can be acquired only by study and practice.
As a rule, all dissections should be carried on as far as
possible with the naked eye ; when this has been accom-
plished, we must then seek the aid of lenses.
The object-glasses of one's Microscope are the best that
can be used for the purpose. An inch lens will be found
especially fitted for the work. A simple Microscope, pro-
vided with a broad stage, and an arm movable by rack and
pinion, for carrying the lenses, is the kind of instrument
usually employed. It should be strongly made, and capable
of bearing a good deal of rough usage.
Dissections may be carried on under the compound Micro-
scope ; but we do not think the beginner would succeed, aa
objects become inverted and motion reversed when seen
through this instrument. If, however, it be provided with
an erector, this difficulty is overcome by the object being
brought into the same position that it occupies when seen by
the n;xked eye.
As most dissections are carried on under water, some kind
of shallow trough is necessary to contain it : watch-glasses
answer the purpose remarkably well. The small white
dishes and covers used for rubbing up colours will be found
very useful ; also some cork bungs on which to pin the
object ; and these last should have their under sides loaded
with lead to sink them in fluid. A great many delicate
dissections may, however, be made in a drop of water placed,
on a slip of glass ; but for all objects of large size, the trcugh,
or some similar contrivance, will be necessary.
121
APPENDIX.
All insects that have been killed a long iime, nnd whose
bodies are hard and brittle, may be softened by immersing
them in the solution already mentioned.
The sting of the bee, wasp, hornet, and the ovipositors of
many flie.s, especially the ichneumons, are very similar in
their structure, and are generally found at the termination
of the abdomen, from which they may be obtained by first
slitting open the body of the insect with the fine scissors,
and afterwards removing the sting by using the scalpel and
needles. One or two of the latter should have their points
curved, which may easily be accomplished by heating the
ends red-hot in the flame of a candle, and bending them
with a pair of small pincers. At first sight the sting pre-
sents nothing to the eye but a horny sheath, tapering to a
point, with a slit broadest at its base and running down the
entire length ; within this sheath, on each side, lies a barbed,
sharp-pointed spear, in large insects capable of inflicting a
severe wound, while the tube in which they are lodged
acts as a steadying rod, and as a channel to conduct a
virulent poison to the wound. The bag containing the
poison is placed at the root of the sting, and is connected
by a narrow neck with the sheath. The difficulty in the
dissection of the sting lies in getting the barbed points out
of the sheath and placing them on each side of it. The
following is the method employed by the writer. The sting
is placed in potash until it loses some of its rigidity ; it is
then transferred to a slip of glass or earthenware trough.
The curved needle-points are essential here. With one, hold
the object firmly on the stage of the Microscope, insert the
point of the other into the opening at the base of the sheath
where it is largest, and gradually draw the point down the
tube ; this will make the opening wider, and dislodge the
barbs ; arrange them on each side of the sheath, place the
sting between two glass slips subject to pressure. When
dry, soak it for a few days in turpentine, and mount in
balsam in the usual manner. A good specimen ought
to show the barbs very distinctly on each side of the
sheath.
It will be found useful to the student to prepare three
specimens of this organ : —
1st. The whole abdomen, showing the position the sting
occupies within it.
2nd. The sting with the barbs lying within the sheath.
3rd. The barbs pulled out of the sheath and placed on
each side of it.
Three such specimens well mounted will enable the student
APPENDIX. 125
to study the structure of this curious organ with advan-
tage.
SPIRACLES (plate 7, figures 212, 213). — These do not re-
quire much dissection. They are generally found on each
side of the abdomen, almost every segment of which possesses
a pair. Excellent specimens are furnished by the dytiscus,
bee, blowfly, cockchafer, and silkworm. To prepare them,
separate from the thorax the abdominal portion of the
insect, and slit it down the centre with the fine-pointed
scissors, draw out the viscera, &c., with the curved needles.
The air-tubes adhering to the spiracles may be detached by
cutting them away with the scissors. Thoroughly cleanse
the horny cuticle by repeated washings, spread it out flat
between two slips of glass ; when dry, immerse it in spirits
of wine or turpentine for a few days, and mount it in balsam.
In this manner the whole of the spiracles of an insect, run-
ning down each side of the abdomen, will be displayed.
TRACHEAE (plate 8, figure 222). — The best method we are
a-cquainted with for obtaining the air-tubes of insects is that
recommended by Professor Quekett : —
"By far the most simple method of procuring a perfect
system of tracheal tubes from the larva of an insect, is to
make a small opening in its body, and then to place it in
strong acetic acid : this will soften or decompose all the
viscera, and the trachea? may then be well washed with the
syringe, and removed from the body with the greatest facility,
by cutting away the connections of the main tubes with the
spiracles by means of the fine-pointed scissors. In order to
get them upon the slide, this must be put into the fluid and
the trachea? floated upon it, after which they may be laid
•out in their proper position, then dried, and mounted in
balsam."
The best specimens are found in the larva of the dytiscua
And cockchafer, and in the blowfly, goat-moth, silkworm, and
house-cricket.
GIZZARDS (plate 8, figures 220, a, b ; 221, a, 6). — Most of
^the insects from which these organs are procured being of
large size, it will be necessary to secure them to one of the
loaded corks by small pins. The dissection should be made
in one of the shallow troughs, filled with weak spirits and
water. Cut the insect open ; the stomach will float out
with the gizzard attached to it, in the shape of a small
bulbous expansion of the size of a pea. Insert the fine
point of the scissors, and cut it open ; the interior will be
found full of food in process of trituration. Empty the
contents of the gizzard, and wash it out well; place it for
12 3 APPENDIX.
a few days in the solution of potash : and, finally, cleanse
it with some warm \\ater and a camel-hair brush. Spread
it out flat between slips of glass ; when dry, place it in
turpentine for a week, and afterwards mount it in
balsam.
The best specimens for displaying the horny teetli with
which the gizzard is furnished are obtained from crickets,
grasshoppers, and cockroaches.
PALATES (plate 6, figures 171, 172, 173, 174). —These,
consist of a narrow kind of tongue, armed with a series of
horny teeth, placed in regular rows. The whelk, limpet^
periwinkle, garden-snail, and the snails found in our cellais
and aquariums, are all furnished with this peculiar appara-
tus, which may be obtained by laying open the body with
the scalpel or scissors. It will generally be found curled up-
near the head, and may be distinguished by its ribbon-like
appearance : patience and skill are necessary to extract it
from the surrounding mass. When properly cleaned, it may
be at once pressed flat and dried between slips of glass.
Many palates polarize well when mounted in balsam ; but
if not intended for polarization, they shculd be mounted in
a preservative fluid, composed of five grains of salt to one
ounce of water.
TONGUES, PROBOSCES, MANDIBLES, AND ANTENNAE
(plate 7, figures 197, 199, 202 to 204) are amongst the most
beautiful objects exhibited by the Microscope. Many of
these, besides the ligula, possess several sharp lancets for
puncturing the skin of animals from whom they derive their
sustenance. To arrange these organs so that each part
may be clearly seen, requires a good deal of delicate mani-
pulation. It is generally more satisfactory to mount the
whole head of the insect. To accomplish this, it must be
softened by immersion in liquor potassce for some time, and
the interior substance got rid of by pressure. To dry it
flat, place it between two slips of glass, which should be held
together by a spring-clip ; soak it for a fortnight or longer
in turpentine, until it becomes transparent, and then mount
it in balsam.
The head of the bee, wasp, dronefly, blowfly, and gadfly,
are all excellent examples of the varied structures of these
suctorial organs.
EYES (plate 7, figures 208, 208«, 210). — The compound
eyes of insects, for the display of their numerous facets,
should be dissected from the head, and macerated in fluid.
The black pigment lining the interior may be got rid of by
washing it away with a camel-hair brush. When quite
APPENDIX. 1
clean, the cornea may be dried and flattened between two
slips of glass. In practice, however, the cornea, from its
sphericity, will be found to have a tendency to fold in plaits,
or to split in halves. To remedy this, cut with the fine
scissors a few notches round its edges ; it may then be
flattened without danger of its either wrinkling or splitting.
When the cornea is very transparent it should be mounted
in a cell with some kind of preservative fluid (spirit and
water will do very well), otherwise the structure will be lost
if mounted in balsam, the tendency of that substance being
to add transparency to every object with which it comes in
contact. But there are many insects in whose eyes the
hexagonal facets are strongly marked : all such will show-
best when mounted in balsam.
HAIKS (plate 7, figures 184 to 191).— These may be
mounted either in fluid or balsam, first taking the precaution
to cleanse them from fatty matter by placing them in ether.
If the hair be coarse and opaque, mount it in balsam ; if
fine and transparent, it should be mounted in a cell, with
some weak spirit.
Sections of hair are made by gluing hairs into a bundle,
and placing it in a machine for making sections. By means
of a sharp knife which traverses the surface, the thinnest
slices may be cut, and each individual section afterwards ean
be separated in fluid. To select the thinnest and best, place
them under the Microscope. The point of a camel-hair
pencil will be found the best instrument for transferring
them to a clean slide. When dry, mount them in balsam, as
usual. Some very good sections of the hairs of the beard
may be obtained by passing the razor over the face a few-
minutes after having shaved.
SCALES OP FISH (plate 6, figures 178 to 180). — These
dermal appendages may be detached' from the skin by a
knife ; and if to be viewed as opaque objects, may be dried
and mounted with no other preparation than cementing over
them a thin glass cover. If intended to be viewed as trans-
parent objects, the scales should be properly cleaned, dried,
and mounted in balsam ; but the most satisfactory way of
exhibiting their structure is to mount them in a cell with
some preservative fluid.
SCALES OF BUTTERFLIES, MOTHS, &c. (plate 8, figures 225
to 229). — Select the wing of a living or recently-killed insect,
gently press it on the centre of a clean glass slide. On re-
moving the wing, numerous scales will be seen adhering to
the slide ; place over them one of the thin glass covers, and
cement it down by tipping lightly the edges with gold size.
128 APPENDIX.
Specimens should be taken from various parts of the wings
-of the same insect, as the form of the scales vary according
to the position they occupy in the wing.
SECTIONS or BONE (plate 8, figure 232). — All hard and
brittle substances from which thin slices cannot be made by
a sharp knife, must be reduced to a transparent thinness
by the process of grinding down. Having selected the bone
from which the section is about to be made, a thin slice
should be cut from it with a fine saw. At first the section,
may be held by the fingers while grinding down one of its
surfaces on a coarse stone ; but when it approaches the thin-
ness of a shilling, it must be cemented by some old and tough
Canada balsam to a slip of glass. Upon the perfect adhesion
of the section to the slide depends in a great measure the
success of the operation. Having reduced the thickness of
the section by a coarse stone or a tile, transfer it to a hone ;
?. few turns will obliterate scratches, and produce an even,
•smooth surface, which may be further polished by rubbing it
on a buff-leather strop charged with putty-powder and water.
"When dry, attach the polished surface to the glass slip : this
gives a firm hold of the section, which would otherwise
become too thin to be held by the fingers. In rubbing down
the unfinished surface, take care that an equal thickness pre-
vails throughout the section. As it approaches completion,
recourse must be frequently had to the Microscope, in order
to determine how much further it is necessary to proceed,
a few turns either way at this stage being sufficient to make
-or mar the specimen. When it has become so transparent
that objects may be readily seen through it, remove it from
the hone and polish it on the strop. To detach it from the
slide when finished, place it in turpentine or ether, both,
being excellent solvents of balsam. Mount in the dry
method, by simply cementing a thin glass cover over it. In
recent bone, this method of mounting, though the most
difficult, is decidedly the best for displaying its structure.
Fossil bone, however, where the interstices are filled with
earthy matter, shows best in balsam.
SPINES OP THE ECHINUS (plate 5, figures 151, 152); SEC-
TIONS OF SHELL (plate 6, figures 165 to 169). — These are
cut and reduced in the same manner as sections of bone ;
but they require greater care in grinding, in consequence of
being more brittle. The polishing, however, may be dis-
pensed with, and the section mounted in balsam.
STONES OF VARIOUS KINDS OF FF.UITS (plate 8, figure 243)
will well repay the labour bestowed in producing good sec-
tions. The gaw, the file, and the hone are the principal
APPENDIX. 1 29
agents need in the reduction of these hard osseous-like
tissues. A perfect section should have but one layer of cells,
which may be admirably seen when mounted in a cell with
weak spirit.
SECTIONS OP WOOD (plate 3, figures 54 to 59). — To make
thin sections of hard wood it will be necessary to employ
some kind of cutting machine. There are several of these,
more or less expensive, but the principle of construction in
all is similar. The wood, after some prepai-ation, and being
cut to the requisite length, is driven by a mallet into a brass
cylinder, at the bottom of which works a fine screw with a
milled head. The wood is pushed to the surface of the tube,
and to any degree above it by the revolution of the screw ;
when a sharp knife, ground flat on one side, is brought with a
sliding motion in contact with it. The slices may be removed
from the knife by a wetted camel-hair pencil, placed in some
weak spirit, and examined at leisure ; the thinnest and most
perfect section being retained for mounting. Green wood
previous to being cut should be placed in alchohol and after-
wards in water. Hard and dry wood may be made suffi-
ciently soft for slicing by first immersing it in water for some
days. Sections of the above may be mounted either in
balsam or fluids. Stems of plants, horny tissues, and many
other substances not sufficiently hard to be ground down,
may be cut into slices of extreme thinness by this handy
instrument. In order to obtain a correct idea of the struc-
ture of wood, bone, and shell, sections should be made in
vertical, transverse, and oblique directions.
CUTICLE or PLANTS (plate 2, figures 42 to 46), HAIES
(plate 3, figures 74 to 88), AND SPIKAL VESSELS (plate 2,
figures 47 to 49), may all be obtained by macerating the
leaves and stems of plants in water, and afterwards dissect-
ing them with the needles. Good specimens of the cuticle,
showing the stomata, may be often obtained by simplv
peeling off the skin with a sharp knife. Hairs may be de-
tached from various parts of a plant by a similar process.
Spiral vessels will, however, require to be separated by the
needles from the surrounding tissues. All delicate vegetable
preparations are best displayed when mounted in a cell with
weak spirit.
Cells for mounting objects in fluid are generally formed
of some kind of varnish upon which the fluid will not act ;
gold-size and Brunswick black are most commonly used.
To form a cell, simply charge a camel-hair brush with the
varnish, and enclose with a broad black ring a small circular
space on the centre of the slide. When quite dry, it is ready
130 APPENDIX.
for use. Place the object, with a small quantity of fluid, in
the cell ; and having lightly touched the edges of the thin
glass cover with gold-size, drop it gently on the specimen ;
the superfluous fluid will escape over the sides of the cell,
and may be removed by small pieces of blotting-paper,
taking care, however, that none of the fluid is drawn from
the interior of the cell ; in which case an air-bubble would
immediately appear. To make the cell air-tight, gradually
fill up the angle formed by the edges of the cover with the
cell, by running several rims of varnish round it. In order
to prevent the cement from running into the cell and spoiling
the specimen, each layer should be dry before another is
placed upon it.
The student should always have a stock of cells on hand
ready for immediate use. Dozens of these cells may be made
in half an hour by an ingenious little turntable, the inven-
tion of Mr. Shadbolt, and which may be obtained for a few
shillings.
The limits of this little work have precluded us from
giving little more than general directions respecting the
permanent preparation of microscopic objects. Our object
has been merely to give a few plain instructions, which, if
carefully followed, will enable the beginner to prepare some
of the most popular objects exhibited by the Microscope.
THE END.
UNIVERSITY OF CALIFORNIA LIBRARY
BERKELEY
Return to desk from which borrowed.
This book is DUE on the last date stamped below.
I
&EC 1 S 1952
JAN 4 '58
Ja2'58LF
OCT 1 8 1958
Oc8'58MS
LD 21-100m-ll,'49(B7146sl6)476
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