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Explantation besonders die struktur und die biologtschen eigenschaftender in vitro ge-z├╝chteten zellen und gewebe. By Giuseppe Levi. Ergeb. D. Anat. U. Entwicklungs. 1934. Bd. 31 S. 125-707

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Ergeb. d. Anat. u. Entwicklungs. 1934. Bd. 31, S. 125-707.
Levi's masterly review is written from the point of view of an
experienced modern histologist who realizes the necessity of studying
living cells and seeks in tissue culture a method of control and analysis
of tissue and cellular structure which cannot be obtained by studying
these cells within the body with the classical histologic methods. Of
the previous reviews of tissue culture, only that of Lewis and Lewis
( '24) has had a predominantly morphological interest. The monographs of Fischer ('30) and Ephrussi ('32) emphasize the studies
on the problems of growth energies of, and effects of changes in
environment on, the tissues, while those of Bisceglie and JuhhszSchaffer ( '28) and Craciun ( '31) attempt t o cover all of the biological
fields studied by the aid of tissue culture.
The work is divided into three main parts: Part I deals with the
general problems of tissue culture growth, including material and
technic; part I1 with the general, and part I11 with the special
morphological and biological properties of cells in tissue culture.
Levi found it impossible to limit himself in this review to purely
morphological observations, but he has not included those problems
of purely biochemical, biophysical, immunological content, etc., although he found it necessary to consider the culture of tumor cells
because of their relations to normal histology.
The details of the many experiments on cellular structure and
changes in vitro (the bibliography requires over forty pages) must
be left to the reader who is interested in particular problems. Here it
must suffice to point out Levi's general point of view and give a few
examples of the subjects studied and conclusions reached. The
contradictory evidence on nearly every question is reviewed critically
and Levi has not hesitated t o express his own views based on his
own work or that of his students. I n general, his conclusions represent fairly most of the evidence t o date, although, naturally, some
of his opinions will not be accepted by all of the workers in this field.
Levi holds that tissue culture is primarily a technic and that the
results obtained by it help us to understand the structure and func105
tions of the cells as they occur in the organism. He disagrees sharply
with those who maintain that tissue culture is a distinct scientific
discipline with its own problems different from those of the organism.
“Ich habe mich veranlasst gesehen, auf diese wichtige Frage morphoiogischer Natnr etwas nachdrucklicher hinzuweisen, weil ich der
Ansicht bin, dass die Neigung, die Ziichtungsmethods als selbststandiges Forschungsgebiet aufzufassen, schadlich fur den Fortschritt der biologischen Wissenschaft ist ; dies fiihrt notwendigerweise
zu einer iibertriebenen Spezialisierung ; das Studium der Zellen in
vitro darf hingegen nicht zu einseitig betrieben werden, sondern wir
miissen vielmehr stets bestrebt sein, Vergleiche zwischen den in vitro
gezuchteten Geweben und den im Organismus verbleibcnden anzustellen. ”
This monograph shows clearly how one of the modern technics of
investigation is changing some of the concepts of the structure of
cell and tissues. Levi points out that the new histology has shown
that tissue cells are not unchangeable systems and that many of the
cell types to be found in the organism can change their morphological
characteristics very greatly in tissue culture. Tissue culture has
proved in several instances that cells which were believed to represent distinct types are merely the morphological expression of different environmental conditions affecting a single cell type. But he
does not believe that it is an advance in biology t o relinquish completely all of the accomplishments of descriptive histology and
cytology: “Form und Struktur sind weder zufallige noch nebensachliche Erscheinungen, wie einige moderne Biologen behaupten,
dazu durch iibertriebene Hoffnungen auf die Anwendung der
physikalisch-chemischen Methoden in der Cytologie verleitet. ”
In his opinion, the continued life of a culture in vitro, as shown
by Carrel, has been the most important result obtained by tissue
culture. He points out that tissue culture has not proved to be the
means of solving many biological problems as was so confidently expected 25 years ago. This failure he ascribes in part to the gradual
and as yet incomplete development of technics.
Among the topics discussed are such problems as the nucleus-plasma
relationships, the mechanism of cellular movement and the causes of
migration, the nature of intercellular connections, cellular constituents,
such as the mitochondria, ground substance, Golgi apparatus, pigment,
etc. Levi concludes that no valid evidence has yet been adduced
showing that the mitochondria change directly into any other cellular
constituent. There is a considerable discussion on changes in the
cell as evidences of differences in metabolic activity and the effects
of changes in the media on the appearance of the cytoplasm. There
follow aections on reproduction, rates of growth, and regeneration.
I n the discussion of the relationships between dediff erentiation and
multiplication, he points out in many places that even though cells
may lose the appearance which they have in the body when they are
placed in tissue cultures, they still may retain many of their original
properties. For instance, rat cells after growing in chick plasma for
many years still react to specific antisera (Fischer, '30). Moreover,
the cells of a tissue if explanted at a time when they have not taken on
a specific structure may differentiate in tissue culture and then dedifferentiate, as for instance, muscle cells. If the tissue is explanted
when it has already taken on specific characteristics, it may maintain
these characteristics and even develop them further. But even here,
the differentiation has not remained permanently.
IIe agrees with Lewis that in epithelium there is no cementing substance between the cells, and that they adhere to one another merely
because their outer layers are particularly adhesive. After a discussion of the general growth properties of the epithelium of the germ
layers, he considers those of the epithelia of the various organs in
vitro, both in mixed cultures and in pure strains where these have
been obtained. I n mixed cultures he believes that epithelium and
fibroblasts remain separate but that the epithelium may dedifferentiate to a large extent.
With regard to the connective tissue cultures, he believes that the
fibroblasts probably can differentiate into other cell types. He does
not agree with Parker's concept that fibroblasts are different in each
organ. He admits that it is difficult in many cases to differentiate
fibroblasts from myoblasts which have dediff erentiated. He points
out that both fibroblasts and epithelium may grow in sheets but that
the tendency is greater for fibroblasts to separate out of the membrane and that, hence, there is no fundamental difference between
these two types of cells in cultures. He believes in the extracellular
origin of fibers, that there is no difference between reticular and
collagenous fibers, and that they do not develop from fibrin.
As might have been expected, probably the most valuable parts
of the book are those dealing with nerve and muscle in tissue culture,
because they have been among the main subjects investigated morphologically by Levi in tissue culture. His general conclusion on cardiac
muscle is that the myoblasts eventually differentiate into cells which
cannot be distinguished from fibroblasts, and he raises the question
whether this is a permanent dedifferentiation or whether the dedifferentiated myoblasts still retain the possibility of developing into
cardiac muscle if given appropriate conditions. Skeletal muscle also
eventually dedifferentiates into cells which cannot be distinguished
from mesenchyme. He believes that in nerve tissue the cells at first
grow as individuals and later develop connections with their neighbors.
He is not sure of the specificity of the staining methods for glia, and
questions the validity of the conclusions of those who hold that,
because certain cells in nervous tissue cultures stain with the IIortega
methods, the cells are of necessity of mesodermal origin.
In the last section of the book dealing with the morphology of
tumor cells in vitro, he points out the marked similarity i n appearance
between tumor cells and normal cells, and the functional differences
between them, particularly as regards rates of growth, liquefaction
of fibrin, etc.
Because of his very extensive experience in general histology and
in tissue culture, Levi is one of the very few histologists capable of
interpreting the value of tissue culture for morphological cytology.
His scholarly, critical monograph is a splendid accomplishment. It
should prove to be absolutely indispensable t o all workers in this
field as well as to anyone desiring an authoritative, orienting review
of the subject.
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