275
quite rudimentary, and the last highly developed, as shown
in the accompanying figure.
Although I had previously communicated researches on
the anatomy of the Heteropoda to the Royal Society of Edinburgh, I had altogether overlooked the buccal teeth of Firola;
and now I am quite sure that further investigation will
reveal similar organs in the other genera of the order.
References to the figure which represents the upper and
lateral parts of the mouth, with the inner surface turned
upwards after the removal of the tongue and buccal mass,
improperly so called.
a. The upper lip. b. The roof of the mouth, c. The
left row of buccal teeth, d. The right row of ditto, e. OEsophageal ruga?.
The NATURE of CONNECTIVE TISSUE.
By DK. W. KRAUSE,
Professor in Gottingen.1
IT is usual to distinguish as the fundamental types of connective tissue two modifications, the ordinary fibrous or
homogeneous and the reticulated. The former is usually
regarded as consisting of a distinctly or indistinctly fibrillated
intercellular substance, and variously formed cells, the connective-tissue corpuscles, imbedded therein; and these are
described sometimes as stellate, sometimes as spindle-shaped
or roundish, sometimes angular and flat. Reticular or
areolar connective tissue is composed of anastomosing stellate
cells (connective-tissue corpuscles), in the interstices of which
is contained fluid with suspended lymph corpuscles.
There would thus be two varieties of connective tissue, the
essential difference between which would be that in the
former the intercellular substance is solid or fibrous, in the
latter fluid. This distinction does not, however, exhaust the
molecular arrangements which are ascribed to the connective
tissue. A third state of molecular aggregation, certainly not
known in the other sciences, is recognised under the name
of semi-solid (festweich), and a fundamental substance of
this kind is ascribed to the homogeneous or gelatinous connective tissue, which is supposed to be connected by transitional forms with the solid or fibrous.
It is obvious, then, that there is only one morphological
attribute common to all modifications of the so-called con1
Translated from ' Deutsche Klinik,' May 20th, 1871, by J. F. Payne.
276
nective tissue; they must all consist of cells and intercellular
substance, the first with any kind of form, the latter of any
kind of consistency. The indefiniteness of the conceptions
which must attach themselves to views so vague is too generally known to need dwelling upon. They are no longer
tenable;—not more so than the whole cell theory itself. To
begin with the reticular connective tissue, this does actually
consist of stellate cells. Their nuclei are oval, their numerous and many times subdivided prolongations are connected
with one another, while lymph circulates in the interstices.
The structure here described recurs in all organs which can
be regarded as belonging to the lymphatic system in a wide
sense of the word. To this system belong especially the
lymphatic follicles which I first described in 1860 as characteristic structures of the human conjunctiva, Bruch
having already observed them in animals.
Now, fibrillated connective tissue, as, for instance, that of
a tendon, consists of the very same nucleated cells [which in
this situation should now be called inoblasts], only the prolongations of the cells are longer, finer, and do not anastomose with one another. By extending themselves exclusively
in two opposite directions, they produce, in virtue of their
parallel and undulating course, the appearance of connectivetissue fibrils arranged in bundles.
If a tendon be macerated in Miiller's solution, or, according to the method proposed by myself,1 in molybdate of ammonia, we obtain, beside fibres, a larger or smaller number
of spiudle-shaped elements. These are the connective-tissue
nuclei of the earlier writers, the nuclei of the connectivetissue corpuscles according to later authorities, so called
because they have a power of resistance to the action of dilute
acids. Sometimes, as is well known, there is observed at
the pointed ends of these spindle-shaped elements a fine
thread-like prolongation. Closer investigation, however,
shows that they pass into very long, delicate, undulating
fibres, which are nothing else than the connective-tissue
fibres of authors. We can accordingly distinguish in every
inoblast its nucleated central portion (formerly called connective-tissue nucleus) and its prolongations (connectivetissue fibres). The somewhat thickened origin of the latter,
at the termination of the spindle-shaped central mass, often
Still contains some protoplasmic granules.
Sometimes only a single fibre is observed at each end. In
other cases this fibre splits up into several, or the spindleshaped corpuscle is itself already divided in its mass. Flat
1
' Archiv fur Anat. u. Phjsiol./ 1871, s. 11.
277
corpuscles also occur, as was formerly brought into prominence by Billroth, and more lately by Ranvier (without
alluding to Billroth). From the ends of these fiat and generally multipolar corpuscles there often proceed many delicate
fibres ; at all events, the inoblasts are sufficiently numerous
in the tendon to give rise by means of their prolongations
to all the connective-tissue fibres.
All the fibres here described of course agree with what
are called connective-tissue fibres in their chemical relations.
More especially do they become invisible when treated with
acids or alkalies, and hence cannot be confounded with the
scanty elastic fibres of the tendon. Their length, which has
never been seriously taken into account, is considerable, perhaps to be reckoned by centimetres, but in no case so great
as that of the tendon itself.
When I proved in 1863 that even the longest muscles of
the human body consist exclusively of spindle-shaped, transversely striated fibres, whose length does not exceed three or
four centimetres, it was natural to ask the question how long
the conuective-ti'ssue fibres of the corresponding tendons
might be. The length of tendons may even, as is known,
exceed a foot, but it can easily be shown that the connectivetissue fibres must be very much shorter.
Since, as was shown above, one or several fibres may proceed from each end of each inoblast, these must be closely
applied to the adjacent fibrils. Starting from the attachment
of a tendon to a bone, it is obvious that each inoblast sends
out fibres in the direction of the muscle. The direction and
abundance of the inoblasts may, however, be easily determined after the addition of acids, since each of them possesses
a central portion (the connective-tissue nucleus), which resists these reagents. As is well known, these nuclei lie in
longitudinal rows. Accordingly, if the prolongations of the
inoblasts, which are near the bony attachment of the tendon,
reached the muscle—that is to say, if they were as long as
the tendon itself—the latter must be tapering or conical. The
apex of the cone would be at the bone, the base at the insertion of the tendon into the muscle. Tendons are, however,
in contradistinction to the conical form, everywhere ofi equal
thickness, forming flattened cylinders. The prolongations of
the inoblasts must accordingly come to an end within the
tendon, and cannot attain any considerable length, since if
they did there must be some indication of a conical shape, at
least near the insertion into bone. If this reasoning be not
admitted, it must be concluded that the fibres or prolongations
of opposite ends of the inoblasts, must at least near the bony
278
or muscular insertion, be very different in length, a supposition which is not supported by observation. The tendon is
accordingly, when looked at as a whole, constructed precisely
like the muscle, if thin inoblasts arranged close one to the
other be mentally substituted for the transversely striated,
spindle-shaped muscular fibres. The facts of embryology
teach, as is well known, that tendons, like muscles, originally
consist of series of spindle-shaped cells ; and from what has
been said above, it results that these relations remain unaltered in. the main through the whole of life.
The connective-tissue fibres are, as has been said, nothing
more than long, narrow radiations of the embryonal spindleshaped cells; but while the latter contain albuminous protoplasma, the radiations consist (apart from the scattered
granules at their origin above mentioned) of homogeneous
gelatinous substance.
The differences between reticular and fibrillated connective
tissue reduce themselves accordingly to the different amount
of interstitial fluid, without reckoning the anastomoses, which
may perhaps be quite wanting in the fibrillated form. The
tendon is composed of spindle-shaped or stellate, or again of
flattened inoblasts, the prolongations of which all run in the
same direction, namely, in the long axis of the tendon. In
the reticular connective tissue the prolongations cross one
another. In all connective tissue which is composed of bundles
the arrangement seen in the tendons is repeated, only that
the prolongations of the inoblasts stretch a little inwards
towards the central axis of the original fibrillar bundle, since
the corpuscles or nucleus-like central portions of the inoblasts
are situated, as is well known, only on the outer envelope of
the primitive fasciculi.
The most important point is that the connective-tissue
fibres of authors are not intercellular substance, but processes
of cells, and there is accordingly no intercellular substance
in fibrillated connective tissue except the tissue-fluid which
permeates the interstices. Since this fluid usually contains
some leucocytes (lymph corpuscles, migratory cells, amoeboid
cells, unattached connective-tissue corpuscles of different
authors), as is certainly not the case in the tendon, it may be
designated as lymph. In this way a perfect analogy with
the reticular connective tissue is established.
According, then, to what has been said, the inoblasts of any
portion of connective tissue are collectively identical with the
connective-tissue nuclei and connective-tissue fibres of earlier
authors, or with the nuclei of connective-tissue corpuscles,
plus intercellular substance of later authors (Virchow). For
279
the stellate connective-tissue corpuscles seen in the cross sections of tendons are, as is now generally recognised, nothing
more than gaps between the connective-tissue bundles. The
nuclei of the inoblasts are equivalent to the nuclei of the
spindle-shaped corpuscles of Langhans, or the nucleoli of
the connective-tissue nuclei of some writers.
The considerations here urged have also a certain pathological interest. For the cellular pathology, founded upon
the connective tissue, rests on the article of faith that the
cells are active in disease, but the intercellular substance
inactive. Tt requires, also, the admission of the identity of
bone, cartilage, and connective tissue, derived from the supposed demonstration of cells and intercellular substance in
all these tissues. But connective tissue has no intercellular
substance, except a little fluid. The fundamental substance
of bone is, moreover, not an intercellular substance, but originates in the cell bodies of the " osteoblasts," fused together
and incrusted. With respect to cartilage, we know, it is
true, nothing more than that it consists of cells and intercellular substance; but its share in the production of bone
must at least appear doubtful, since the importance of the
interstitial [not intercellular] growth has been recognised even
in the hollow bones. Finally, as to the part played by connective tissue in the so-called proliferations of cells, no one
will now doubt that the inoblasts are as innocent in this
respect as what were formerly called stellate connective-tissue
corpuscles.
It remains to speak of certain subordinate varieties of connective tissue which may be included under the two main
varieties.
What is called homogeneous connective tissue is said to
consist of round or stellate cells and homogeneous intercellular substance. With improved optical aids to observation this tissue may be resolved into its constituents.
In the apparently gelatinous tissue of the tadpole's tail
stellate anastomosing cells and a homogeneous fundamental
substance have been distinguished; but the latter substance
is in reality fluid enclosed in a fine network of threads, which
are in connection with the inoblasts or stellate cells. These
threads are the ultimate prolongations of the processes of the
cells, but migratory cells may make their way in the midst
of the fluid.
A modification of the reticular connective tissue, which is
usually called adenoid or cytogenous tissue, deserves special
mention. As long ago as 1860, that is, long before this was
regarded as a special variety of tissue, I described the
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NEW SER.
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diffusion of lymph corpuscles in connective-tissue membranes as " lymphatic infiltration " (of the conjunctiva, the
intestinal villi, &c). A similar construction of connective
tissue is seen in the neighbourhood of lymphatic follicles
wherever these exist, and in part is due to larger lymphatic
channels filled with leucocytes.
In the lymphatic follicles, and especially in their central
portions, the above-mentioned reticular connective tissue
occurs. The small absolute size of the inoblasts themselves,
the shortness and manifold ramifications of their processes,
are combined with a denser accumulation of the inoblasts,
which are placed closer together, and from all these causes
that peculiar appearance results which so readily distinguishes
the tissue of the lymph follicles from all other connective
tissue. Henle was, therefore, not correct in regarding the
tissue of the lymphatic follicles as ordinary connective tissue,
or in denying the existence of its numerous nuclei.
When the interstices of the reticular connective tissue are
filled with round cells and albuminous fluid, a soft, spongy
consistency of the tissue results. This is the case not only
in the interior of lymphatic follicles, but also in other tissues
which belong to the lymphatic apparatus—for instance, in
the intestinal villi. The fundamental tissue consists of the
fine prolongations of scanty inoblasts, which are stretched
between the blood capillaries of the villus. In the meshes
lie numerous lymph corpuscles, separated from one another
by spaces filled with fluid (lymph). The comparatively
small number of inoblasts in an equal volume, and the apparently larger quantity of fluid in proportion to the suspended
corpuscles, distinguish this tissue from the reticular tissue of
the spherical lymph follicles.
Instead of homogeneous, semi-solid fundamental substance,
there is, then, in reality a network of very fine threads filled
with fluid. Although invisible when fresh, owing to their
having almost the same refractive index as the surrounding
fluid (lymph), these threads readily become visible by the
action of reagents (chromic acid, dilute soda, even water).
As in other cases, a so-called semi-solid substance shows itself,
on more accurate investigation, to be made up of solid parts
and fluid.
The investigations here communicated date from the
summer of 1870; their publication was delayed by the war.
The important result is that the connective-tissue fibres are
prolongations of cells, not intercellular substance, and that
there is in this respect a uniformity in all kinds of connective
tissue.