25. _Special Methods._—Having in the preceding pages entered at some
length into the general subject of section-cutting, it remains for us
now to consider those special methods of preparation which the
peculiarities of certain objects demand. In order to keep the bulk (and
consequent price) of this manualette within due bounds, we shall,
without further preface, proceed to the description of these methods, in
doing which every endeavour will be made to employ such brevity of
expression as may be consistent with perfect clearness of meaning. As
the most convenient plan, the objects here treated of will be arranged
in alphabetical succession.
26. _Bone._—Both transverse and longitudinal sections should be
prepared, the former being the prettier and most interesting. After
prolonged maceration in water, all fat, etc., must be removed and the
bone dried, when as thin a slice as possible is to be cut off in the
desired direction, by means of a very fine saw. If the section so
obtained be placed upon a piece of smooth cork it may, with the aid of a
fine file and the exercise of care, be further reduced in thickness. It
is then to be laid upon a hone moistened with water, and being pressed
gently and _evenly_ down upon it with the tip of the finger (protected,
if necessary, by a bit of cork or gutta-percha), it must be rubbed upon
the stone until the desired degree of thinness has been attained.
Finally, in order to remove scratches and to polish the section, it
should be rubbed upon a dry hone of very fine texture, or upon a strop
charged with putty-powder. After careful washing in several waters the
section must be allowed thoroughly to dry, when it may be mounted by the
_dry method_ in the following manner:—A ring of gold-size must, by means
of the turn-table, be drawn in the centre of a slide, and the slide put
away in a warm place for several days (the longer the better), in order
that the ring may become perfectly dry and hard. When this has been
accomplished the section is to be placed in the centre of the ring, and
a covering circle of the requisite size having been cleaned, this must
have a _thin_ ring of gold-size applied round its margin. The cover is
now to be placed in position and gently pressed down, a spring clip
being employed, if necessary, to prevent it from moving. In about
twenty-four hours another layer of the varnish should be applied, and
the slide afterwards finished in the manner already described (§ 24).
The above method is also applicable to the preparation of sections of
_teeth_ and also of _fruit-stones_ and other hard bodies, which are
incapable of being rendered soft enough for cutting.
As the process just described, however, is both troublesome and tedious,
it is much better for ordinary purposes to have recourse to the
_decalcifying method_, by which means sections in every way suitable for
the examination of the essential structure of bone may be obtained with
ease. To carry out this plan a piece of fresh bone should be cut into
small pieces and placed in a solution made by dissolving 15 grains of
pure chromic acid in 7 ounces of distilled water, to which 30 minims of
nitric acid s. g. 1.420 are afterwards to be added. Here they should
remain for three or four weeks, or until the bone has become
sufficiently soft to cut easily, the fluid being repeatedly changed
during the process. From this solution they must be transferred to
methylated spirit for a few days, when a piece may be selected, imbedded
in paraffine, and cut in the microtome (§ 12). Some of the sections
should be mounted, unstained, in spirit. For this purpose a cell of
gold-size, as above described, must first be prepared and filled _full_
of a mixture of spirit of wine one part, and distilled water three
parts. Into this the section must be carefully placed and the cover
applied, the same precautions for the exclusion of air-bubbles being
taken which were recommended when speaking of mounting in glycerine (§
16). When the cover is in position a ring of gold-size must be laid on,
repeated when dry, and the slide afterwards finished in the ordinary
manner. It will also be advisable to stain some of the sections with
carmine (§ 14), or picro-carmine (§ 42), and mount them in glycerine.
_Teeth_ may also be treated by the decalcifying method, but in this case
it must be remembered that the enamel will dissolve away.
27. _Brain._—The best hardening fluid is that recommended by Rutherford,
and is made by dissolving 15 grains of pure chromic acid and 31 grains
of crystalized bichromate of potash in 43 ounces of distilled water.
Small pieces of brain, which have previously been immersed for
twenty-four hours in rectified spirit, should be placed in about a pint
of this solution, where they must remain for five or six weeks, the
fluid being repeatedly changed during the process. If by this time they
are not sufficiently hard the induration must be completed in alcohol.
Sections are easily cut in the microtome by the paraffine method (§ 12).
These may advantageously be stained in a solution of aniline blue, made
by dissolving 1-1/2 grain of aniline blue in 10 ounces of distilled
water, and adding 1 drachm of rectified spirit (_Frey_). As this stain
acts very rapidly two or three minutes’ immersion will generally be
found long enough. The sections must then be mounted in balsam (§ 23).
28. _Cartilage._—The method to be employed in the preparation of
cartilage will entirely depend upon the nature of the staining agent, to
the action of which the sections are to be submitted. Thus, if the
elegant _gold method_ is to be followed, it is necessary that the
cartilage should be perfectly fresh; whilst if any of the other staining
agents are to be employed the tissue may have been previously preserved
in alcohol. An excellent object on which to demonstrate the gold process
is to be found in the articular cartilage of bone. It is a very easy
matter to obtain from the butchers the foot of a sheep which has just
been killed. The joint is to be opened, and the bones dissociated, when
they will be seen to have their extremities coated with a white
glistening membrane—this is the _articular cartilage_. Exceedingly thin
slices must be at once cut from it, and as only small sections are
required, a sharp razor may be used for the purpose, the blade being
either dry or simply wetted with distilled water. The sections as cut
are to be transferred to a small quantity of a half per cent. solution
of chloride of gold in a watch glass. Chloride of gold may be purchased
in small glass tubes hermetically sealed, each tube containing 15
grains, and costing about 2s. If, however, the student requires only a
small quantity of the staining fluid he need not be even at this small
expense, for as photographers for the requirements of their art always
keep on hand a standard solution of chloride of gold of the strength of
one per cent., a little of this may readily be obtained, and diluted to
the required degree. After the sections have been exposed to the action
of the staining fluid for about ten minutes they may be transferred to a
small beaker of distilled water, and exposed to diffused light for about
twenty-four hours, when they must be mounted in glycerine (§ 16).
Sections of cartilage may also be examined, without being stained, in
which case the field of the microscope should be only very feebly
illuminated. Or carmine staining (§ 14) may be resorted to—these
sections show well in glycerine, or if the staining be made very deep,
even Canada balsam may be employed, and with fair results.
Microscopists are indebted to Dr. Frances Elizabeth Hoggan for the
description of a new method of staining, which we have found especially
suited to the treatment of cartilage. The agent employed is _iron_, and
the process, which is very simple, is as follows. Two fluids are
necessary—(1) tincture of steel; (2) a two per cent. solution of
pyrogallic acid in alcohol. A little of the former is to be poured into
a watch glass, and into this the sections, after having been previously
steeped in alcohol for a few minutes, are to be placed. In about two
minutes the iron solution is to be poured away and replaced by solution
No. 2. In the course of a minute or two the desired depth of colour will
have been produced, when the sections are to be removed, washed in
distilled water, and mounted in glycerine. The results obtained by this
process are very beautiful, the colour produced being a very fine
neutral tint, of delightful softness. The process also answers admirably
in the case of morbid tissues, and we have now in our possession some
sections of ulcerated cartilage tinged by the iron method, in which the
minute changes resulting from the ulcerative disintegration are brought
out with wonderful distinctness.
As the structure of cartilage differs according to its purpose and
situation, the student will find his time profitably employed in a
careful examination of the following forms (α) _hyaline_—articular and
costal; (β) yellow fibro-cartilage—epiglottis, or external ear; (γ)
_cellular_—ear of mouse. Sections of the _intervertebral_ ligaments
should also be made, in which the different kinds of cartilage may be
examined side by side with each other.
29. _Coffee Berry_ affords sections of great beauty. The _unroasted_
berry should be soaked for hours or days in cold water until
sufficiently soft; then imbedded in paraffine, and cut in the microtome
(§ 12), the section being made in the direction of the long axis of the
berry. Put up in glycerine, or stain rather strongly with carmine, and
mount in balsam. The same method of treatment may also be applied to
other hard berries or _seeds_.
30. _Fat._—Adipose tissue may be hardened in alcohol, cut in paraffine,
and mounted in glycerine. If the tissue has been injected the sections
may be mounted in balsam, and are then very beautiful objects, showing
the capillary network encircling the fat cells.
31. _Hair._—Longitudinal sections are readily made by splitting the hair
with a sharp razor. It is more difficult to cut the hair transversely.
This, however, may easily be done in the following manner. The hairs
having previously been well soaked in æther to remove all fatty matters,
a sufficient number of them must be selected to form a bundle about the
thickness of a crow quill. This bundle, after being tied at each
extremity with a bit of thread, is to be immersed for several hours in
strong gum (§ 18,) to which a few drops of glycerine have been added. On
removal, the bundle must be suspended by means of a thread attached to
one end of it, in a warm place until sufficiently hard, when it is to be
imbedded and cut in paraffine (§ 12). Each section, as cut, is to be
floated off the knife into methylated spirit. From this it is with the
aid of the spoon (§ 14) to be transferred to a slide, the spirit tilted
off, a drop of absolute alcohol added, when, after a minute or two, this
also is to be drained off, the section treated with clove oil, and the
mounting completed as described in § 23.
32. _Horn_ varies very much in consistence, in some instances having a
cartilaginous character, whilst in others it is almost bony. In the
latter case, sections will have to be ground down in the manner
explained when speaking of bone (§ 26). Where the texture is less dense,
recourse may be had to prolonged steeping in hot or boiling water; in
some cases it will be necessary to continue the immersion for several
hours. When sufficiently soft the piece of horn may, by means of bits of
soft wood, be firmly wedged into the tube of the microtome, and sections
cut with a razor, or what is better, with a broad and very sharp chisel.
The sections are to be put between glass slips, held together by
American clips (or pegs), and put away for two or three days in order to
become thoroughly dry. After well soaking in good turpentine or benzole,
they must be transferred to slides, the superfluous turpentine drained
off, and chloroform-balsam added, etc. (§ 23). Sections of horn should,
of course, be cut in different directions, but for examination with the
polariscope those cut transversely yield by far the most magnificent
results. _Hoofs_, _whalebone_, and allied structures should also be
treated by the above method.
33. _Intestine._—The method to be pursued with _sections_ has already
been described (§ 18). The ileum, however, is a very pretty object when
a portion of it is so mounted as to show the _villi erect_. To do this
it is necessary to cement to the slide, by marine glue, a glass cell of
sufficient depth. This should have been prepared some time beforehand,
so that the cement may be perfectly dry and hard. The cell is now to be
filled with turpentine, and the piece of ileum (having been previously
passed through methylated spirit and absolute alcohol into turpentine)
is gently placed into it, having the villi uppermost; pour some pure and
rather fluid balsam on the object at one end, and gradually incline the
slide, so as to allow the turpentine to flow out at the opposite side of
the cell, till it is full of balsam. Then take a clean cover, and having
placed upon it a small streak of balsam from one end to the other, allow
it gradually to fall upon the cell, so as to avoid the formation of
air-bubbles (§ 17), and finish the slide in the usual manner.[15] Or,
the intestine may be dried, and mounted _dry_, in a cell with a
blackened bottom, for examination as an opaque object.
Footnote 15:
Ralf.
34. _Liver._—Small pieces of liver may be very successfully hardened by
immersion in alcohol, beginning with weak spirit and ending with
absolute alcohol. Cut and mount as usual.
35. _Lung_ must be prepared in chromic acid (§ 5). For the cutting of
sections the freezing microtome (§ 18) is of especial value, and should,
therefore, be used. If, however, the student be not provided with this
instrument, he must proceed as follows. A small piece of lung,
previously deprived of all spirit, is to be immersed until thoroughly
saturated in solution of gum (§ 18). A small mould of bibulous paper (§
2), only just large enough to receive the piece of tissue, having been
prepared and filled with the mucilage, the specimen is to be transferred
to it. The mould, with its contents, is now to be placed in a saucer,
into which a mixture of about 6 parts of methylated spirit and 1 part of
water (_Schäfer_) is to be poured until the fluid reaches to within
about a third of the top of the paper mould. In the course of several
hours the surface of the mucilage will begin to whiten and solidify. As
soon as this occurs more dilute spirit must be poured into the saucer,
until the mould is completely submerged. In a day or two the gum will be
found to have acquired a suitable consistence for cutting, when it must
be removed from the spirit, the paper mould peeled off, and the mass
imbedded and cut in paraffine, the sections being afterwards treated as
if they had been obtained by the freezing method (§ 18). If the
solidification of the gum should proceed too slowly, a few drops of pure
spirit may be added to the contents of the saucer. If, on the other
hand, the gum should become overhard, it will be necessary to put into
the saucer a few drops of water, and repeat this until the required
consistence be obtained.
36. _Muscle._—Harden in chromic acid, and cut in paraffine. Transverse
sections may be made to show the shape of the fibrils. Longitudinal
sections will only be required in the case of injected tissues, when
such sections will be found very elegant, showing, as they do, the
elongated meshes of capillaries running between and around the muscular
fasciculi. Mount in glycerine or balsam. To see the transverse striæ
characteristic of voluntary muscle, a very good plan is to take a bit of
pork (cooked or fresh), and by means of needles to teaze it out into the
finest possible shreds. If these be examined in water or glycerine, the
markings will be shown very perfectly.
37. _Orange-peel_, common object though it be, is not to be despised by
the microscopist. Transverse sections must be prepared by the gum method
(§ 35). These sections are not to be subjected to the action of alcohol
(as this would destroy the colour), but after _drying_ between glass
slides they must be soaked in turpentine and mounted in balsam. We shall
then have a good view of the large globular glands whose office it is to
secrete that essential oil upon which the odor of the orange depends.
38. _Ovary_ may be prepared in the same manner as liver (§ 34).
Sections, which are to be cut in paraffine, may be stained with carmine,
and mounted in glycerine or balsam. Apart from all scientific value, we
know of no slide for the microscope which, even as a mere object of
show, surpasses in beauty a well-prepared section of _injected_ ovary,
showing the wondrous Graafian vesicles, surrounded by their meandering
capillaries.
39. _Porcupine Quill._—Soften in hot water, cut in paraffine, and mount
in balsam. Much (in our opinion _too_ much) lauded as an object for the
polariscope.
40. _Potato._—From the large amount of water which it contains thin
sections cannot be cut from the potato in its natural state. It must,
therefore, be partially desiccated, either by immersion in methylated
spirit for a few days or by exposure to the air. Sections may then
readily be obtained by imbedding and cutting in paraffine. Such sections
mounted in balsam are very beautiful, the starch being seen _in sitú_,
whilst if polarized light be employed each granule gives out its
characteristic black cross.
41. _Rush_ is to be prepared and cut as orange-peel (§ 37). Transverse
sections of this “weed” furnish slides of the most exquisite beauty.
42. _Skin._—To prepare skin for section a piece is to be selected which,
after having been boiled for a few seconds in vinegar, must be stretched
out on a bit of flat wood, and being maintained in position by pins be
allowed to remain until thoroughly dry. Then imbed in paraffine, and cut
_exceedingly_ thin transverse sections. These may be stained in carmine,
but more beautiful results are obtained if picro-carmine be employed.
Sections of skin, when stained by this agent are much increased both in
beauty and instructiveness; for the several constituents of the tissue
becoming tinged with different colours are readily distinguishable from
each other, whilst the contrast of colouring forms a pleasing picture to
the eye. The method of preparing picro-carmine is very simple, though it
sometimes yields a solution not altogether satisfactory. The best
formula with which we are acquainted is that given by Rutherford,[16]
and if due care be taken in following it out failure will generally be
avoided. “Take 100 c.c. of a saturated solution of picric acid. Prepare
an ammoniacal solution of carmine, by dissolving 1 gramme in a few c.c.
water, with the aid of excess of ammonia and heat. Boil the picric acid
solution on a sand bath, and when boiling add the carmine solution.
Evaporate the mixture to dryness. Dissolve the residue in 100 c.c.
water, and filter. A clear solution ought to be obtained; if not, add
some more ammonia, evaporate, and dissolve as before.” Sections may be
exposed to the action of this fluid for a period varying from fifteen to
thirty minutes, then rapidly washed in water, and mounted in glycerine.
They may also be mounted in balsam, care being taken in that case to
shorten as much as possible the period of their immersion in alcohol, so
that no risk may be run of the picric acid stain being dissolved out.
Footnote 16:
“Practical Histology,” 2d edit. p. 173.
If it is intended to study the structure of the skin with anything like
thoroughness, portions must of course be examined from different
localities, in order that its several varieties and peculiarities may be
observed. Thus the _sudoriforous_, or sweat glands, may be found in the
sole of the foot, whilst the _sebaceous_ glands are to be sought in the
skin of the nose. The _papillæ_ are well represented at the tips of the
fingers,[17] whilst the structure of the shaft of the _hair_, together
with that of the follicle within which its root is enclosed, as also the
muscles by which it is moved, are to be studied in sections of skin from
the scalp or other suitable locality.
Footnote 17:
It is well, in connection with these papillæ, to bear in mind a fact
pointed out by _Frey_, namely, that the tips of the fingers frequently
become, _post-mortem_, the seat of extensive natural injections;
hence, in sections from this region, we frequently obtain good views
of distended capillaries without having been at the trouble of
previously injecting them.—_Frey_, “Microscopical Technology.”
43. _Spinal Cord._—The spinal cord, say of a cat or a dog (or if
procurable, of man), after being cut into pieces about half an inch in
length, may be hardened in the usual chromic acid fluid (§ 5). As it is
peculiarly liable to overharden and become uselessly brittle, the
process must be carefully watched. Its further treatment is the same as
that of brain. These sections may be stained very satisfactorily by the
_ink process_, for communicating details of which we are indebted to the
kindness of Dr. Paul, of Liverpool. The agent usually employed is
Stephenson’s blue-black ink, which, for this purpose, must be quite
fresh. As in the case of carmine, two methods of staining may be
adopted—either rapid, by using concentrated solutions, or more
prolonged, according to degree of dilution. For the reasons previously
given (§ 14), slow methods of staining are always to be preferred, as
yielding the most beautiful results, yet, for the purposes of
preliminary investigation, it is often convenient to have recourse to
the quick process. To carry out the latter plan, an ink solution of the
strength 1 in 5—10 parts of water is to be freshly prepared, and the
sections exposed to its action for a few minutes. For gradual staining
the dilution must be carried to 1 in 30—50, and the time of immersion
prolonged to several hours, the sections being occasionally examined
during the staining, so that they may be removed just as they have
acquired the desired tint. When a satisfactory coloration has been
obtained, the preparations should be mounted in dammar or balsam (§ 23).
One advantage of this method of staining is, that definition is almost
as good by artificial light as by day.
44. _Sponge_ may readily be cut after being tightly compressed between
two bits of cork; or its interstices may be filled up by immersion
either in melted paraffine (§ 11) or in strong gum (§ 18), and then cut
as usual.
45. _Stomach_ requires no special method of hardening (chromic acid).
Sections should always, when practicable, be cut in the freezing
microtome. In default of this, proceed in the manner as directed for
lung (§ 35). Both vertical and horizontal sections will, of course, be
required. If the preparation has been injected, the latter are
particularly beautiful. Stain with carmine or aniline blue (§ 27), and
mount—if for very close study, in glycerine—if injected and for a “show”
slide, use balsam.
46. _Tongue._—Harden in chromic acid, imbed and cut transverse sections
in paraffine. As, however, the paraffine is apt to get entangled amongst
the _papillæ_, whence it is afterwards with difficulty dislodged, it
will be as well before imbedding to soak the tongue in strong gum for a
_few minutes_, and afterwards immerse in alcohol till the gum becomes
hardened, so that the delicate papillæ may thus be protected from the
paraffine by a surface-coating of gum. The best staining agent is
picro-carmine (§ 42). Sections of _cat’s_ tongue near the root, when
thus stained, furnish splendid objects. Sections should also be made of
the _taste-bulbs_, found on the tongues of rabbits. These are small oval
prominences, situated one on each side of the upper surface of the
tongue near its root. They should be snipped off with scissors, and
vertical sections made in the direction of their long axis. Stain with
carmine or picro-carmine, and mount in glycerine or balsam.
47. _Vegetable Ivory_.—After prolonged soaking in cold water may readily
be cut in the microtome. The sections should be mounted in balsam, and
though not usually regarded as polariscopic objects, nevertheless, when
examined with the _selenite_, yield very good colours.
48. _Wood._—Shavings of extreme thinness may be cut from large pieces or
blocks of timber, by means of a very sharp plane. In this way very good
sections may be procured of most of the common woods, as oak, mahogany,
“glandular wood” of pine, etc. Where however, the material to be
operated upon takes the form of stems, roots, etc., of no great
thickness, they should, after having been reduced to a suitable
consistence (§ 4), be imbedded in paraffine, and cut in the microtome.
Before imbedding it must not be forgotten to immerse the wood to be cut
in weak gum-water (§ 11), this precaution being of great importance,
especially in the case of stems, etc., the bark of which is at all rough
and sinuous. If the sections are to be mounted _unstained_, they are
usually put up in weak spirit (§ 26). A very general method also of
dealing with this class of objects is to mount them _dry_ (§ 26). This
plan, however, cannot be recommended, for however thin the sections may
be, the outlines, when this process is adopted, always present a
disagreeable black or blurred appearance. To avoid this we may have
recourse to Canada balsam, but the ordinary method of employing it must
be slightly modified, a drop of chloroform being substituted for the
clove oil (§ 23), otherwise this latter agent will cause the section to
become so transparent as to render minute details of structure difficult
to recognize. A better plan, perhaps, is to stain the section with
carmine or logwood, and mount in balsam by the ordinary process. The
best course to follow, however, especially in the case of transverse
sections, is the _double staining_ method.[18] For this purpose the
sections in the first place must be subjected to the action of a
solution of chloride of lime (1/4 oz. to a pint of water) until they
become thoroughly bleached. They must then be soaked in a solution of
hyposulphite of soda (one drachm to four ounces of water) for an hour,
and after being washed for some hours, in several changes of water, are
to be transferred for a short time to methylated spirit. Some red
staining fluid is now to be prepared by dissolving half a grain of
Magenta crystals in one ounce of methylated spirit. A little of this
solution being poured into a small vessel of white porcelain (§ 14), the
sections are to be immersed in the dye for about thirty minutes. They
are now to be removed, and after _rapid_ rinsing in methylated spirit to
remove all superfluous colour, they must be placed in a blue staining
fluid made by dissolving half a grain of aniline blue in one drachm of
distilled water, adding ten minims of dilute nitric acid and afterwards
sufficient methylated spirit to make two fluid ounces. The sections must
be permitted to remain in this solution for a very short time only, one
to three minutes being generally sufficient, for as the action of the
dye is very energetic, it will, if too long exposure be allowed,
completely obliterate the previous coloration by the magenta. After
being again _rapidly_ rinsed in methylated spirit, as much of this as
possible must be drained off, and the sections put into oil of
_cajeput_, whence, in an hour, they may be transferred to spirits of
turpentine, and after a short soaking, mounted in balsam.
Footnote 18:
See a paper by Mr. Styles in the “Pharmaceutical Journal,” also
“Monthly Microscopical Journal” for August, 1875. [For a very
exhaustive paper on this subject by the late Dr. Beatty, of Baltimore,
Md., see “American Journal of Microscopy” for June, 1876.
If the student will carefully carry out the above process, his trouble
will be amply repaid by the beautiful results obtained, for by its means
he may, with ease, prepare for himself a series of slides of such value
as to constitute a worthy addition to his cabinet.
The preceding list by no means represents all the objects, sections of
which will be found interesting to the microscopic student. Such was not
its purpose—had it been so, the enumeration might have been prolonged
almost indefinitely. The end in view was to bring under the notice of
the reader only those substances the cutting of which is accompanied by
difficulty; and even of this class the space at our disposal has been so
limited that we have been unwillingly compelled to pass over many, and
dwell only on such as possess a typical character.
------------------------------------------------------------------------
NOTES.
----------
NOTE A., Page 14.
RANGOON oil is not found in this market. It is a variety of naphtha or
petroleum found at Rangoon, in Asia, and contains a variable percentage
of solid paraffin. Kerosene with a very little paraffin dissolved in it,
would undoubtedly answer the same purpose.
Good sperm oil or tallow (free from salt) will serve quite as well. It
is scarcely necessary to caution the reader that all oily matter should
be removed from the knife before it is used for cutting sections. This
is best effected by dipping it in hot water and carefully wiping it.
NOTE B., Page 15.
METHYLATED spirit is alcohol which contains a small percentage of
methyl. This renders it unfit for use in the manufacture of liquors or
even chloroform, but does not injure it as a preservative fluid. The
scientific men of Great Britain have the privilege of obtaining this
fluid free from duty, and consequently they make very general use of it.
In this country the student of science has no such privilege, and must
use the more expensive alcohol. This however is but of a piece with
other restrictions placed upon scientific pursuits in this country,
where men like Marshall Jewell and Hannibal Hamlin have influence enough
to pass laws which prohibit the exchange by mail of microscopic
specimens, which pass freely in every other civilized country.
True methyl alcohol, or methylated spirits, is not to be had in this
country, and therefore whenever this liquid is directed to be used in
English books the American microscopist must substitute good alcohol.
What is sold for “methyl alcohol” is wood spirit or wood naphtha, and
will not serve the purposes of the microscopist, though it answers well
enough for spirit lamps, making varnishes, etc.
NOTE C., Page 20.
THE method described in the text is generally known as the “free-hand”
method, and although it is not generally employed for the production of
cabinet specimens or slides that are intended for sale, yet it possesses
so many advantages that every student should endeavor to acquire the art
of cutting sections without the use of the microtome. For purposes of
study such sections are quite equal to the best of those usually found
on sale, and for the encouragement of beginners we may add that we have
seen sections cut by the free-hand method which for size, thinness and
accuracy, excelled any that we have ever seen produced with the
microtome. Indeed Schäffer distinctly affirms that no microtome can
equal the skilled hand in the production of thin sections.
NOTE D., Page 22.
THE mere existence of a binding screw should be no objection, and where
bushings are employed it is sometimes necessary. But as the author well
observes, a binding screw cannot be used to secure histological
preparations.
NOTE E., Page 22.
A STILL better system is where the section-knife is held in a frame
which slides on the plate so that the edge is kept just above the
surface. In this way the edge of the knife is never dulled by grinding
on glass or metal. A common mistake in this form, however, is to raise
the cutting edge too far above the surface of the plate. This gives rise
to great irregularities.
NOTE F., Page 22.
AS the size of the sections which it may be desired to cut, varies
within wide limits, the best microtomes made in this country are
furnished with as many as three tubes or “bushings,” fitting one within
the other, and in this way the hole may be partially filled up and thus
reduced in size. This enables us to obtain a range of from one inch and
a quarter, suitable for large histological preparations, to one-eighth
of an inch for such objects as hair sections.
NOTE G., Page 37.
KNIVES FOR CUTTING SECTIONS.
SUCCESS in cutting sections depends more upon the excellence of the
knife that is used than upon any other one point, and therefore the art
of keeping the knife in good order is one which should be acquired by
every microscopist, even at the cost of considerable time, study and
labor. As a stepping stone to the acquisition of this art, there are
certain general principles which must be thoroughly understood before we
can hope for success in practice. These principles are simple, and when
once clearly stated, quite obvious, but they are frequently overlooked.
Cutting instruments act in two ways—either as simple wedges or as a
series of wedges, the latter being generally known as the saw-like
action. It is frequently stated in school philosophies that the edges of
_all_ cutting instruments are toothed like a saw, and that they act like
a saw; this is evidently not the case with many, such as the axe, the
chisel, the plane, etc., and it is not even true of several to which it
is frequently applied, such as the razor, the penknife, etc. The action
can be said to be “saw-like” only when the teeth act as independent
wedges and remove a small portion of the substance acted upon, the
portion being known as _saw-dust_. Now in cutting sections of wood with
a sharp razor, where but a single stroke is used to carry the cutting
edge across a section, say half an inch in diameter, the edge of the
razor does not act like a saw; none of the material is removed except
the section itself; in other words, there is no saw-dust. That the edge
of the knife or razor is not even, is very easily proved by means of the
microscope, but it will be found that the notches and projections form a
series of lancet-shaped knifelets, each one of which acts just as does
the blade of a penknife when drawn over a piece of wood or a quire of
paper. Now if we lay a quire of paper on a board and draw the edge of a
penknife over it, we will cut down through the paper, not by sawing but
by a moving wedge. It is precisely in this way that the little
lancet-shaped teeth on the edge of a razor act when the latter is used
to cut a section.
If we further examine the edge of the razor, we will find that the
bottoms of the notches are comparatively blunt; if therefore we press
the razor directly forward we soon press these blunt portions of the
general edge against the material to be cut, and the resistance becomes
so great that the material is actually crushed or torn. This would not
happen if we had an absolutely perfect edge—one without any notches.
This being practically unattainable, however, we must endeavor to make
up for it by a sawing motion, (though not a sawing action) at the same
time seeking to avoid as much as possible those saw-like features which
render this motion necessary. We have dwelt at length upon this point
because so much has been written comparing the edge of a razor to that
of a saw, that some persons actually advise us to give the edges of our
knives and razors a saw-like character, under the impression that by so
doing they will work better. This is a fallacy; the best work will be
obtained from the smoothest and most perfect edge, provided the latter
is thin enough.
If the material of which our cutting instruments are made would allow
it, that is to say if it was perfectly hard, perfectly rigid and
incapable of being crushed or torn apart, the proper shape of a cutting
instrument would be a wedge of the most acute form possible. But since
the steel which we use is limited in its hardness and its power of
resisting crushing and bending influences, the blades of our knives must
have a certain strength or thickness, depending upon the character of
the material to be cut. For very hard substances the knife must be stout
and the edge ground to a comparatively obtuse angle; for moderately soft
substances, such as wood, the angle may be more acute, while for very
soft tissues the thinnest blade and the sharpest edge are most suitable.
[Illustration: Fig. 1.]
The various angles to which cutting tools of different kinds are ground
are shown in the accompanying illustrations, which explain themselves.
[Illustration: Fig. 2.]
In the diagrams just given, the sides of the wedge are carried in
straight lines to the very edge. In practice, however, this is never
done, there being two strong objections to such a form. In the first
place if the sides were as shown in the figures, every time the tool was
ground or set, the entire side would have to be ground off, and this
would involve great labor. But another difficulty, quite as great, would
occur in the use of the instrument, for since the wedge keeps growing
constantly and proportionately thicker, the friction between the sides
of the wedge and the material would rapidly become very great. Therefore
most cutting edges are ground to a second angle, much more obtuse than
the first, and it is this second angle which forms the true cutting
edge. And it is obvious that the mass of material required to carry out
the ultimate angle in any case is wholly unnecessary, for if the tool be
strong enough at _a b_ (Fig. 2) it will certainly be strong enough at _c
d_. An extreme illustration of this principle is shown in the cold
chisel used for cutting iron, the edge of which is shown in Fig. 2, and
the angle of 80° to which it is ground is carried out by dotted lines.
The angle which the sides of the chisel (not the sides of the extreme
cutting edge however) make with each other is 25°.
[Illustration: Fig. 3.]
[Illustration: Fig. 4.]
There are two methods by which this change of angle may be made, one of
which is shown in the cold chisel just figured, and the other in the
razor of which a section is shown in figures 3 and 4. In the case of the
cold chisel it will be seen that the tool is first formed to a thin
straight wedge which is afterwards changed to one that is much more
blunt. This answers very well where the ultimate angle is comparatively
large or blunt, as is the case with penknives, table-knives,
carving-knives, etc. But where the ultimate angle is very small this
plan does not answer well, and the method shown in Fig. 3 is generally
adopted. Here the ultimate angle is such that lines touching the extreme
edge and the back of the blade are perfectly straight and form the
actual cutting angle. In this case, therefore, the relief is obtained by
hollowing out the sides of the blade, and this is done to various
extents, the extremes being shown in figures 3 and 4. Fig. 3 shows a
section of a razor ground on a stone 12 inches in diameter, which is as
large as is generally used for this purpose. Fig. 4 is a section of a
razor ground on a four-inch stone—the smallest in general use. This
method of changing the angle is of course substantially the same as the
first, merely differing in the mechanical device used, but it affords
this important advantage that in the subsequent honing and stropping
processes the back of the razor forms a perfect guide by which the
ultimate angle may be determined. This is not the case with the cold
chisel or the carving-knife, in both of which cases the eye and hand
alone determine the cutting angle, which is therefore apt to become
irregular or even rounded—the worst form of all. This will be more
easily understood from the following engravings where A, Fig. 5, shows a
penknife blade, as applied to an oilstone for the purpose of giving it
the final edge. The angle here shown is considerably greater than that
generally used, but the principle is the same. It is evident that if, in
moving the blade back and forth on the stone we allow it to rock or
change the angle which the blade makes with the stone’s surface, the
edge will become rounded as shown in Fig. 6—a form which for delicate
work is useless.
If the blade be laid down flat as at B, Fig. 5, the labor of wearing
away the superfluous metal will be enormous. But if the blade be hollow
as Fig. 7, (where the hollow is, for clearness of illustration, slightly
exaggerated) then the ultimate angle may be formed quickly and
accurately, there being no danger of the angles being changed on account
of want of skill on the part of the operator.
[Illustration: Fig. 5.]
[Illustration: Fig. 6.]
[Illustration: Fig. 7.]
[Illustration: Fig. 8.]
In some cases one side is left quite flat and the other side is ground
to two or sometimes three angles, as in the carpenter’s chisel, a
section of which is shown in Fig. 8, where _a a_ shows the angle made by
the body of the blade; _b b_ the angle of the bevel formed by the
grindstone, and _c c_ the angle of the cutting edge which is formed by
the oilstone. In this case the flat side A B forms a straight guide and
enables the workman, in cutting, to make straight, clean work. In
sharpening such a tool on the oilstone the flat side is always laid flat
on the oilstone and merely smoothed off,[19] and the skill of the
workman is chiefly shown in the accuracy with which he forms the angle
_c_ B _c_. The dexterity with which skilled workmen can effect this by
the hand alone is astonishing, but in the hands of those who have had
but little practice the edge infallibly becomes rounded as shown in Fig.
6. Therefore wherever a knife with a flat side is used, no attempt
should ever be made to grind this flat side on the hone. Such an attempt
will almost always result in an edge so irregular that it will be almost
impossible to cut a good section with it. But if the under side of the
knife be left truly flat, we will have the very best tool that can be
had for use with the microtome. Unfortunately, however, it is very
difficult to get a knife with a truly flat surface, that is, one that is
perfectly “out of wind” as mechanics say. As a general rule the flat
sides of knives are not true planes but irregularly curved surfaces;
consequently when laid on a plane surface, such as the table of a
microtome, they rock, and the edge is in contact with the table at some
points and separated from it at others, and the points which are in
contact change as the knife is moved diagonally across the table. This
makes the section irregular and worthless. But a really good knife with
a perfectly true flat side is such a valuable tool that a good deal of
effort may be profitably expended in getting it, and when once obtained
never let the flat side be touched by a grindstone, or more than touched
by a hone. It is not absolutely necessary, however, that the sides of a
delicate knife should be curved, provided the knife is used for cutting
very soft materials. An angle of 10° or even 5° gives a pretty stout
blade when carried back three-quarters of an inch, as may be seen by
examining Fig. 1, and the guiding action of the very thick back may be
obtained by means of an artificial guide, applied like the brass backs
of tenon saws. Such an arrangement is shown in Fig. 9, and has been
found very effectual.
Footnote 19:
Holtzapffel tell us that chisels that are required for paring across
the end grain of moderately soft wood are considered to hang better to
the work when they have a very slight keen burr or wire edge thrown up
on the face or flat side of the tool. But this does not apply to
section knives.
When the knife is to be honed, the back is applied and fastened by means
of two or three set screws. When laid on the hone, the edge of the knife
and the lower surface of the back form the guide and regulate the
cutting angle. In this way we can use a broad, thin blade and yet secure
great accuracy in honing it. Such a blade has this advantage also, that
it is not so liable to be rounded and thus injured by stropping as one
in which the relief is obtained by hollowing out the sides.
[Illustration: Fig. 9.]
Such, then, are the general principles which govern the construction of
cutting tools, including the section knives used by microscopists. We
will now give a few practical directions for selecting a knife and
putting and keeping it in order.
In selecting a knife for cutting sections, regard must be had to the
texture of the material that is to be cut. To attempt to cut delicate
sections of soft tissues with the stout knives which are suitable for
cutting sections of woody fibre would be to destroy the sections, while
to reverse the operation and cut sections of wood with thin, delicate
knives would result in the ruin of the knife. We have seen a most
excellent knife seriously injured by an attempt to cut material that was
too hard for it. The knife was very thin, and had proved most excellent
in cutting sections of such material as kidney, liver, etc. An attempt
was made, against our protest, to cut a section of an apple-shoot, the
wood of which was mature. Before the knife had gone half way across, it
bent, dug into the wood and broke, leaving an ugly gap in the middle.
Experienced section-cutters know this very well, but young microscopists
are not so familiar with the facts just stated, and the point is too
important to be overlooked. Those, therefore, who devote themselves to
microscopical studies, or who expect to make sections of materials of
several kinds, differing in hardness, etc., must provide themselves with
knives of different degrees of strength.
For common work, good razors are as good as anything, provided they can
be obtained with straight edges. Where razors are not suitable, recourse
must be had to the surgical instrument maker, though we are sorry to say
that there are but few in this country that know how to forge, temper
and grind a decent knife. Most of our dealers in instruments do not make
the instruments they sell; they import the goods they sell with their
names stamped on, and thus get a reputation as manufacturers; a special
order they are unable to fill respectably. There are some exceptions,
but of the majority of dealers what we have written above is true.
The points which specially demand attention in a knife for cutting
sections are these: 1. Quality of the steel used; 2. Temper; 3. Form of
the blade.
Of the quality of the material of which a knife is made, nothing can be
determined except by actual trial. The old tests of staining with acids,
examining with the microscope, etc., are worthless, or at least too
crude and uncertain to be of any practical value. Color changes with the
degree of polish that is produced, and, in short, there is no reliable
guide. The purchaser must depend entirely upon the reputation of the
manufacturer. There is plenty of good steel to be found; the trouble
lies with the cutlers. They are careless and in haste, and as a
consequence they burn the steel or fail to work it sufficiently, and the
result is a useless tool.
The steel may be of the very best quality, however, and well forged, and
yet the knife may fail from being badly tempered—too soft or too hard.
If too soft, the edge is soon dulled; the knife requires to be
frequently honed, and the time wasted in keeping it in order is a
serious drawback. If too hard, it is impossible to give it a keen edge,
for the metal crumbles away as soon as it is honed or stropped very
thin, and the edge becomes ragged and dull. Good steel, well forged, may
be so tempered that it will neither crumble nor become rapidly dull.
Much may be learned on this point from careful inspection of the edge,
and trial on a piece of horn, such as an old razor handle. When drawn
over a clean piece of horn once or twice the edge of a soft knife is
completely dulled; if well-tempered it should scarcely lose its
keenness. Again, when laid flat on the thumb nail and pressed, the edge
ought to bend up without breaking or crumbling, and at once, when the
pressure is removed, resume its original shape. The extent to which
extreme hardness and durability, or toughness, may be combined, is well
shown in the famous Toledo sword-blades. One of these blades will shear
through an iron nail without having its edge perceptibly dulled, and yet
so tough and springy is it that it may be coiled up into a hoop of
several folds without breaking or receiving any permanent set. If we
could only get section knives of stuff like this, it would be a pleasure
to work with them.
After all, however, the only test of these two points, material and
temper, is a fair trial in actual practice. Of the form of the blade,
however, it is easy to judge, and there are a few points which are
frequently overlooked and which give rise to errors that are attributed
to other causes.
In the text we are told that “It is essentially necessary that the back
and edge of the blade be strictly parallel to each other.” The author
undoubtedly knew what the correct form should be, but the definition he
has given is not a correct mathematical statement of the conditions
involved. These are as follows:
_The edge must form a straight line, and both the edge and the under
side of the back must lie in the same plane._
Let us consider these conditions somewhat carefully.
Since the hole in which the material to be cut is imbedded, is always
circular, and since the blade is generally pressed forcibly against the
table of the microtome, it is obvious that if the edge of the knife be
curved it will sink into the hole to a greater or less depth according
as it is further from the centre of the hole or nearer to it. To explain
this let us refer to the greatly exaggerated drawing given in figure 10
where the edge of the knife, _a_, _b_, is shown in two different
positions covering the hole of the microtome. The least degree of
reflection will show that as the knife passes towards the centre from _a
b_ to _aʹ bʹ_, it will have a tendency to turn on the back as on a
hinge, and the middle of the edge will sink deeper into the hole as it
approaches the centre of the latter. The section will therefore vary in
thickness and prove useless. This difficulty can be obviated only by the
use of a straight edge like _e f_, which will always lie in the same
plane.
[Illustration: Fig. 10.]
If the knife were perfectly rigid, and the curved edge and back lay
entirely in the same plane, this difficulty would not occur to any great
extent. But since a curved edge rarely lies wholly in the plane of the
back of the knife, and since the blades of most knives, especially those
thin ones used for cutting sections of soft tissues, yield a little to
pressure, and since this pressure is never exactly the same, it is
impossible to prevent irregularities from occurring.
While it is not necessary that the back of the knife and the cutting
edge should be parallel to each other, it is absolutely necessary that
they be in the same plane, or, as mechanics say,—“out of wind.” If this
condition be not observed, the blade will rock on the microtome table as
it passes over it, and irregularity in thickness of section will result.
A slight knowledge of geometry will enable any one to see that these
statements are strictly accurate.
As regards other points in the form of the knife, we refer to what has
been previously said when discussing the general principles which should
govern the construction of cutting tools.
We now proceed to give a few practical directions for sharpening knives
and razors and keeping them in order.
Section knives, during the process of sharpening, are subjected to three
distinct processes: 1, Grinding; 2, Honing; 3, Stropping.
Grinding is one of the most important, though it is probable that it
will rarely be undertaken by the microscopist himself. More knives and
razors are spoiled in grinding than in any other way. We have now in our
possession an excellent knife, which in an evil hour we entrusted to a
New York cutler, and received it back utterly ruined, the temper being
entirely taken out of the blades! Some of our readers may wonder at
this, but unfortunately it is too true. The cutler, to save time and
trouble, too frequently holds the blade against the stone with such
force that it becomes over-heated, especially when he is a little
careless and allows the supply of water to fall short.[20] The owner
does not find this out until he discovers that the knife is ruined,
because nothing is more easy than to cool the blade and grind off the
tell-tale blue spots. When charged with his rascality, the cutler always
denies it and lays the blame on a “soft spot in the steel”—a miserable
subterfuge—too transparent to deceive the least experienced.
Footnote 20:
Nothing is more easy than to heat a thin rod or stout wire red hot by
holding it against a dry grindstone rapidly revolving. We have often
kindled fire in this way.
The only protection against this is either to entrust the knife to a man
of known carefulness and integrity, or to stand over him while he does
it. If the knife be ground under the owner’s eye, no fear need be
entertained, because it is easy to insist upon the use of plenty of
water.
The grindstone used for section knives should be of fine grain, and it
should run true and be very straight across the face, otherwise it will
be impossible to grind the knife true, and this, as we have seen, is a
necessity.
Every microscopist that expects to do much at cutting sections must
learn to hone his own knife or razor. Of the various hones in use the
famous Turkey oilstone is said to be altogether the best. It is,
however, very difficult to get it genuine and in sufficiently large
pieces. We therefore use the German hone-slate, a softer, yellow stone
of wonderful fineness and cutting power. The ordinary whetstones are
altogether too coarse, and as for artificial stones and strops, they may
do for coarse work and common razors for _scraping_, but they will not
do for knives used for section-cutting. If any of our readers should be
so fortunate as to possess a good, old-fashioned Turkey oilstone with a
fair sized surface, let them think much of it. It is invaluable. Years
ago, when working on some investigations that required the use of very
sharp knives, we were offered, by an old English carpenter, the use of a
real Turkey stone. We have never since found anything that did its work
so quickly and so well.
To merely mention the substitutes for Turkey oilstone would fill some
pages. We therefore confine ourselves to the German hone. It is obtained
from the slate mountains in the neighborhood of Ratisbon, where it
occurs in the form of a yellow vein running vertically into the blue
slate, sometimes not more than an inch in thickness, and varying to
twelve to eighteen inches. After being quarried it is sawed into thin
slabs, which are usually cemented to a similar slab of the blue slate as
a support, and the combined stones are then set in a wooden frame and
fitted with a cover, also of wood. Unlike the Turkey oilstone, the
Arkansas stone, and some others, the German hone is soft and easily
scratched and worn. It must therefore be carefully preserved, and as the
_flatness_ of the hone is an important point, it should never be used
for anything but section knives.
Having purchased a hone, the first thing to do is to see that it is
perfectly true; that is, that its surface is a perfect plane. If hollow
or twisted, it is useless until made straight. It may be tested by means
of two steel or wood straight-edges, and the method of doing this, which
is very simple but difficult to describe, the microscopist can learn
from any cabinet maker or carpenter. If the hone be not true it must be
made so, and this is best done by grinding it with emery on a slab of
marble or, better still, a plate of cast iron which has been planed
true. (Waste castings with planed surfaces may be found in most machine
shops, and may be either borrowed or purchased for a small sum.) If the
hone is very uneven, coarse emery may be used at first; then finer must
be taken, and so on until the surface of the hone is not only true but
very smooth. This involves considerable labor, but it cannot be avoided
if a _true_ edge as well as a sharp one is desired, and hence our advice
to use the hone for nothing but section knives. Accuracy in a penknife
or a razor for shaving is of no consequence; in a section-knife it is a
_sine qua non_.
The surface of the hone must not only be true and smooth, it must also
be clean and free from dust and grit, a single particle of which may
spoil the work of hours. It should therefore, when not in use, be kept
constantly covered. It is always used with oil, and this oil should be
of a kind that does not readily dry up. Good sperm is excellent, and so
is purified neat’s-foot oil. Avoid kerosene, soap and water, and similar
fluids, which are so frequently recommended, especially under the guise
of new discoveries. They have all been tried and found wanting. After
use, the stone should be carefully wiped clean, fresh oil being applied
when it is next used. It must never be used without a liberal supply of
oil, otherwise it will become glazed and will no longer act on the
steel.
The hone being in good order, the blade is laid flat on it and moved
over its surface with circular sweeps. The method of doing this is
easily acquired, and is best learned by watching an expert cutler at
work. If we could only hit it, the perfection of this operation would be
to wear down the sides of the blade until they just met; they would then
form a keen and perfect edge. Unfortunately we cannot always hit this
point exactly; we are apt to overdo the matter just a little, and then
comes up the _bête noir_ of beginners—the “wire edge.” This is caused by
the metal of the blade bending away from the hone as soon as it becomes
of a certain degree of thinness. Once it does this it cannot be worn off
by the hone, and the only way to remove it is to draw the edge of the
knife or razor across a piece of horn or hard wood. After removing the
wire edge in this way, give the blade one or two sweeps on the hone and
then strop it. If the blade be very soft, the wire edge comes very
quickly and easily, and is very hard to get rid of. On very hard blades
the wire edge is not so apt to make its appearance. It comes, however,
on very excellent blades. It may be avoided in a measure by driving the
blade edge-first over the hone, and indeed the blade should always be
sharpened most in this way. And since the backward and forward strokes
are always nearly equal, as regards space passed over, this is
accomplished by exerting a greater pressure on the forward than on the
backward stroke.
This wire edge is a nasty thing when it breaks off on the hone. Unless
removed it will very speedily ruin a fine knife, therefore look out for
it and wipe off the hone carefully if you have any suspicion that
particles of steel have broken off the blade and got on to it.
In honing, as in everything else, however, nothing but practice will
impart skill, and he who intends to become an expert should practice on
a few old razors, grinding, honing and stropping them himself, until he
has acquired the art of giving them an edge far keener than most of the
razors ordinarily used for shaving.
The last operation to which the knife is subjected is that of stropping,
and as the blade should be stropped after every section, it becomes
important that our tools should be good and that we should know how to
use them. By having two or three knives we can always avoid grinding and
honing the blades ourselves, for it is then easy to hire the work done,
and half a dozen knives will last a careful worker a long time with
merely the aid of a good strop. But the strop he must use himself.
Fortunately no great skill is required in stropping, but the strop must
be a good one and is best home-made.
Our readers have doubtless seen the “Cheap John” strop-vendors take a
rough table knife, strop it on one of their “patent” strops and cut a
hair with it. Nevertheless such a knife, sharpened in that way, would
not cut good sections, and such a strop is not just the thing for giving
the finishing touch to a section-knife, even though the label does say
that it is “intended for surgical instruments.”[21]
Footnote 21:
The finest emery paper, glued on a strip of wood and used as a strop,
will impart to a razor an edge sufficiently keen to enable it to
remove the beard, and if paper three or four degrees coarser be used,
a very dull knife or razor may be sharpened, and afterwards stropped
on the finer emery until it is keen enough to cut a hair. But it will
be found that cutting edges produced in this way are not smooth enough
for section-cutting.
The strop should never be used with the intention of removing metal so
as to thin the edge of the knife. This is the proper function of the
hone, and those who depend most on the hone and least on the strop, will
always succeed best. The strop is used in the first place for
_smoothing_ off the edge, and in the second for removing that incipient
dullness which always comes from even the slightest use. It is true that
in the latter case the strop trespasses somewhat on the functions of the
hone, but only to a very slight extent, and stropping should never be
carried so far as to require more than a very few strokes.
[Illustration: Fig. 11.]
[Illustration: Fig. 12.]
The best material for a strop is good calf-skin, well tanned, and firmly
glued to a strip of wood with the hair side out. The leather should be
hard, otherwise it will rapidly round the edge of the knife. The way in
which this occurs is readily understood from figures 11 and 12. In Fig.
12 the leather is seen to rise up behind the edge of the blade as the
latter passes over it, so that instead of two plane facets meeting at an
angle of from 15° to 20° as left from the hone, (Fig. 12) the edge has
become considerably rounded and the ultimate angle of the cutting edge
is nearly or quite doubled. The hardest and firmest leather should
therefore be chosen, avoiding of course any leather that has been made
hard and unpliable by the action of water or other agents. Two sides
will be found enough for a strop. On one the leather should be kept
clean, while the other should be thoroughly impregnated with fine
grained, but very hard rouge or crocus.[22] Rouge is an artificial oxide
of iron prepared by exposing sulphate of iron to heat. The hardness of
the resulting powder depends upon the temperature to which it has been
exposed, and this temperature is very well indicated by the color which
the rouge assumes. Bright red or crimson rouge is soft and will not cut
steel; hard rouge, suitable for polishing steel, is purple in color, and
this quality should therefore be chosen. Great care should be taken to
see that it is free from gritty particles, and it should be well rubbed
into the leather in a dry state. All mixtures of grease and oil with
abrasive substances should be eschewed. If the leather be of good
texture and the rouge hard and fine, a very few strokes will suffice to
impart the last degree of smoothness and keenness to the blade.
Footnote 22:
Rouge may be purchased from dealers in watch-makers’ tools. Those who
cannot procure it readily may very easily prepare it for themselves.
Full directions may be found in the “Amateur’s Handbook.” New York:
Industrial Publication Company.
Since grit and dust would soon spoil the strop, it should be kept
carefully covered and protected. The rouge will require occasional
renewing, which may be done by sprinkling a little lightly over the
surface and rubbing it in with the finger. Consequently we find that the
best and most convenient holder for rouge is a bottle with some fine but
porous fabric tied over the mouth of it, forming as it were a sort of
dredge. Over the bottle mouth and its cover should be tied a paper cap
to keep out dust.
We have thus endeavored to give, in as simple a manner as possible, such
information as will guide the microscopist to the acquisition of skill
in this most important but generally despised department of his art. We
are told by the biographer of Swammerdam that a great deal of his
success was to be attributed to his skill in sharpening his fine knives
and scissors. The same is also stated of other noted workers, and yet
none give even the slightest directions to the novice who desires to
follow in their footsteps. There is not to our knowledge a single book
in the English language which treats fully of this subject, with perhaps
the exception of Holtzapffel’s work on “Mechanical Manipulation,” and
this has long been out of print. As previously stated, however, it is
only by practice that the necessary finger-skill can be acquired, but
this skill is well worth acquiring at any cost. The man who depends upon
cutlers and knife grinders will never make satisfactory progress.
NOTE H.
We are inclined to believe that the difficulty of enclosing glycerine
does not arise from the dissolving action of this liquid, so much as
from the great adhesiveness which exists between it and glass. Oily
cements are of course attacked by glycerine, but shellac and several
other gums are insoluble, and drying oils, if well oxidized are also
insoluble. Where cells are used they must be first firmly attached to
the clean slide, and the cement should also be brought into direct
contact with the clean cover. Glycerine does not evaporate at ordinary
temperatures, and consequently wherever the slide or cover is soiled
with it, no cement will ever adhere until the glycerine has been wiped
off. There is no prospect of its drying.
NOTE I. Page 48.
The solution here referred to, and which is known as Kleinenberg’s
solution, is made in the following way:
(1.) Make a saturated solution of crystallized calcium chloride in 70
per cent. alcohol, and add alum to saturation. (2.) Make also a
saturated solution of alum in 70 per cent. alcohol. Add (1) to (2) in
the proportion of 1:8. To the mixture add a few drops of a saturated
solution of hæmatoxylin in absolute alcohol.
This solution may be used in very many cases for staining sections, in
place of the ordinary watery solution of logwood alum. It may, if
required, be diluted with the mixture of 1 and 2. The stained sections
are placed at once in strong spirit.
------------------------------------------------------------------------
INDEX.
Acetic acid, 38
Adipose tissue, 63
Æther microtome, 24
Air-bubbles, 40, 55, 62
Alcohol, 17, 19
absolute, 54
Balsam, Canada, 46, 51
to clean from slide, 55
Beale’s carmine fluid, 33
Bell’s cement, 41
Blue staining fluid, 60
Bone, 16, 57
decalcified, 58
Bottles for media, &c., 48
Brain, 59
Brunswick black, 41
Capillary attraction, 55
Carmine staining, 32
Carpenter, Dr., 37, 41
Cartilage, 60
Cells, to make, 59
Centring slide, 38
Chloroform-balsam, 51, 54
Chromic acid, 17
Clove oil, 51, 54
Coffee berry, 62
Cover, applying, 37
German plan, 39
Crochet-needle holders, 39
Double staining, 73
Dry mounting, 58, 65, 72
Fat, 63
Finishing slide, 54
Fibro-cartilage, 62
Freezing method, 42-47
Fresh tissues, to cut, 15-17
Fruit stones, 58
Gardner, Mr., 25, 31
Gelatine cement, 41
Glycerine, 37, 38
Gold staining, 58
Gum, imbedding in, 22, 66
strong, 43
weak, 31, 71
Hair, 63-69
Hæmatoxylon, _see_ Logwood
Hand-sections, 19
Hardening agents, 19
Hoggan, F. Elizabeth, Dr., 61
Hone, 26, 57
Horn, hoofs, &c., 16, 64
Hyaline cartilage, 62
Ice, for freezing, 43
Injections, to harden, 19
Ink staining, 70
Intestine, 42, 43, 64
Iron staining, 61
Kay, J. A., Mr., 52
Kidney, 17
Klein’s _lifter_, 35
Knife, section, 25, 30
Leaves, &c., to cut, 12
Ligaments, intervertebral, 62
Lime, carbonate of, 37
Liver, 65
Logwood staining, 47
Lung, 43, 65
Martindale’s logwood fluid, 47
Media, mounting, 38
Methylated spirit, _see_ Alcohol
Microtome, 21
choice of, 22
Microtome, employment of, 29
freezing, 43, 44
imperfection in, 23, 46
Rutherford’s, 31
Muscle, 66
Needles, microscopical, 39
Orange-peel, 67
Ovary, 67
Papillæ of finger, 69
Paraffine, adhering to sections, 27
imbedding in, 20, 26
mixture, 26
_rising_ in tube, 23
shrinks in cooling, 29
Paul, Dr., 70
Pathological specimens, 19, 62
Picro-carmine, 59, 68, 72
Porcupine quill, 67
Potato, 67
Preparation of animal tissues, 16
vegetable tissues, 15
Prussian blue pigment, 38
Rangoon oil, 14, 47
Razors, 20, 26, 29, 30
Rush, 78
Rutherford’s microtome, 24, 31
“Practical Histology,” 43
Salicylic acid, 44
Salt, for freezing, 45
Schäfer’s “lifter,” 35
“Practical Histology,” 48
Scissors, section, 13
Sebaceous glands, 69
Section-cutter, _see_ Microtome
Section-knife, 24
Sections, thickness of, 31
to dehydrate, 52
to transfer, 33
Seeds, 63
Skin, 68
Sperm oil, 44
Spinal cord, 69
Spirit lamp for balsam, 53
weak, 36, 59
Sponge, 71
Spoon, section, 35, 54
Staining agents, 31
Strop, razor, 26, 29
Stomach, 71
Sudoriferous glands, 69
Taste-bulbs, 71
Teeth, 16, 58
Tongue, 71
Tubes, collapsible, 56
Valentin’s knife, 14
Vegetable ivory, 72
tissues, to prepare, 12
Vessels, porcelain, 33
Water-bath, cheap, 29
Whalebone, 64
White zinc cement, 56
Wood, 72
------------------------------------------------------------------------
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Just Published. 1 Vol., 12mo. Neatly Bound in Cloth, Gilt Title. Price
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HOW TO USE THE MICROSCOPE.
A Simple and Practical Book, intended for beginners.
BY JOHN PHIN,
_Editor of “The American Journal of Microscopy.”_
Second Edition. Greatly Enlarged, with 50 illustrations in the text,
and 4 full-page engravings printed on heavy tint paper.
CONTENTS:
WHAT A MICROSCOPE IS.—Different Kinds of Microscopes.—Simple
Microscopes.—Hand Magnifiers.—The Coddington Lens.—The Stanhope
Lens.—Raspail’s Microscope.—The Excelsior Microscope.—Twenty-five cent
Microscopes and how to make them.—Penny Microscopes.
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Objectives.—French Achromatic Objectives.—Objectives of the English
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HOW TO CHOOSE A MICROSCOPE.—Microscopes for Special Purposes.—Magnifying
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ACCESSORY APPARATUS.—Stage Forceps, Animalcule Cage, etc.
ILLUMINATION.—Sun Light.—Artificial Light.—Bulls-Eye Condenser.—Side
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HOW TO USE THE MICROSCOPE.—How to Care for the Microscope.
HOW TO COLLECT OBJECTS.—Where to find Objects.—What to Look for.—How to
Capture Them.—Nets.—Bottle-Holders.—Spoons.—New Form of Collecting
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THE PREPARATION AND EXAMINATION OF OBJECTS.—Cutting Thin Sections
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Section-Cutter.—Sections of Rock.—Knives.—Scissors.—Needles.—Dissecting
Pans and Dishes.—Dissecting Microscopes.—Separation of Deposits from
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Objects.—Refractive Power of Liquids.—Covers for Keeping out
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FINISHING THE SLIDES.
May be obtained from any Bookseller or News Agent, or will be sent by
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------------------------------------------------------------------------
_GENESIS AND GEOLOGY._
--------------
THE CHEMICAL HISTORY
OF
The Six Days of Creation.
BY JOHN PHIN, C. E.,
EDITOR OF “THE AMERICAN JOURNAL OF MICROSCOPY.”
_1 Vol., 12mo._ _Cloth._ _75 cents._
--------------
The following are a few of the Opinions of the Press:
This is a small book, but full of matter. * * * We think this book is
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are investigating these subjects.—_The Presbyterian_ (Philadelphia).
The author gives a new solution of this difficult question, and
certainly presents many very plausible arguments in support of his
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A very candid and ingenious essay.—_Christian Union_ (H. W. Beecher’s
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------------------------------------------------------------------------
THE YOUNG SCIENTIST,
A Practical Journal for Amateurs.
=ISSUED MONTHLY. Price 50 Cents per year.=
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------------------------------------------------------------------------
=WHAT PEOPLE SAY OF US.=
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“The YOUNG SCIENTIST is a handsome monthly magazine, each number
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“It is a journal which should be in the hands of both young and old, and
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“This publication is a new launch, and it is very gratifying to witness
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------------------------------------------------------------------------
THE AMERICAN
JOURNAL OF MICROSCOPY,
AND
_POPULAR SCIENCE_.
--------------
PROSPECTUS.
The object of the JOURNAL OF MICROSCOPY is to diffuse a knowledge of the
best methods of using the Microscope; of all valuable improvements in
the instrument and its accessories; of all new methods of microscopical
investigation, and of the most recent results of microscopical research.
The JOURNAL does not address itself to those who have long pursued
certain special lines of research, and whose wants can be supplied only
by elaborate papers, which, from their thoroughness, are entitled to be
called monographs rather than mere articles. It is intended rather to
meet the wants of those who use the microscope for purposes of general
study, medical work, class instruction, and even amusement, and who
desire, in addition to the information afforded by text-books, such a
knowledge of what others are doing as can be derived only from a
periodical. With this object in view, therefore, the publishers propose
to make the JOURNAL so simple, practical and trustworthy, that it will
prove to the advantage of every one who uses the microscope at all to
take it.
ILLUSTRATIONS.—The JOURNAL will be freely illustrated by engravings
representing either objects of natural history or apparatus connected
with the microscope.
TRANSACTIONS OF SOCIETIES.—THE AMERICAN JOURNAL OF MICROSCOPY is not the
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Microscopy, and is in good form and size for binding, no better medium
can be had for preserving the scientific records of any society. Matters
of mere business routine we are frequently obliged to omit for want of
room.
EXCHANGES.—An important feature of the JOURNAL is the exchange column,
by means of which workers in different parts of the country are enabled,
without expense, except for postage, to exchange slides and materials
with each other.
=TERMS.=
During the first two years of its existence, the subscription to the
AMERICAN JOURNAL OF MICROSCOPY was only fifty cents per year, but at the
request of more than two-thirds of the subscribers, the size of the
JOURNAL has been doubled, and the price raised to
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● Transcriber’s Notes:
○ Missing or obscured punctuation was corrected.
○ Typographical errors were silently corrected.
○ Inconsistent spelling was made consistent when a predominant form
was found in this book; otherwise it was not changed.
○ Forms of the name Schäfer were regularized to match the title page
of his “A Course of Practical Histology.”
○ Text that was in italics is enclosed by underscores (_italics_);
text that was bold by “equal” signs (=bold=).