Download Karl Ernst von Baer in Italy (1845-46)

Karl Ernst von Baer’s 225° jubilee
1792 - 2017
Karl Ernst von Baer in Italy (1845-46) and his
relationships with Italian naturalists
von Baer’s travel in Italy in 1845
Filippo De Filippi
1814 - born in Milan on 20th April
1836 – takes his degree in Medicine at the University of
Pavia, where he remains to carry out scientific research as an assistant to the chair of Zoology
1837-40 – works at the University Museum founded by Lazzaro
Spallanzani and prepares a catalogue of the snakes
1840 – shifts to Milan to work at the Natural History Museum
1848 – gets the chair of Zoology at the University of Turin
and delivers the inaugural lecture “On the importance
of zoological studies”
1862 – takes part in an official mission sent to Persia as
the director of the scientific group. Upon his return
to Italy he writes a number of articles on the flora
and fauna of Persia and publishes his diary of the
expedition “Notes of a voyage to Persia”
1864 – made a senator of the Kingdom of Italy, on 11th
January gives the public lecture “Man and the Apes”
by which he popularizes the Darwinian theory in Italy
for the first time
1865 – embarks on the warship “Magenta” to take part in a
government-sponsored scientific voyage to circumnavigate the globe and collect plant and animal
specimens
1867 – dies on 9th February at Hong Kong
Route of the ship "Magenta"
Giandomenico Nardo
1802 – born in Venice on 4th March
1807-20 – attends the primary and secondary school at the
Seminary of Chioggia and is introduced to the study
of natural sciences by his uncle, abbot Giuseppe M.
Nardo
1822 – enrols on the courses of Medicine at the University
of Padua and starts to cooperate with his professor
of Natural History Andrea Renier
1827 – takes his degree in Medicine
1828 – becomes assistant to the chair of Natural History with
the task of reorganizing the zoological collections
1831 – revises the systematics of the Adriatic sponges and
shifts to Venice
1832 – goes to Vienna to improve his medical qualifications
and study the zoological collections of the Imperial
Museum
1833 – goes back to Venice and establishes the new class of
Spongiaria
1840 – becomes a member of the Royal Institute of Veneto of
Sciences, Letters and Arts
1849-65 – director of a charitable institution for abandoned
children
1868 – director of the Committee of Agricolture and Fish
Farming
1877 – dies in Venice on 7th April
Chondrosia reniformis (Nardo, 1847)
During his stay in Trieste in 1845-46 von Baer established contacts with several local naturalists, including the botanists
Bartolomeo Biasoletto (1793-1858) and Muzio de Tommasini (1794-1879), and Heinrich Koch ( 1815-1881), an amateur
zoologist with special interest in marine invertebrates. In 1846 von Baer helped Koch in arranging his collection of
zoological specimens which became the core of a private museum, the "Zoological-Zootomical Cabinet“, where it was
exhibited free until the end of 1848. Koch was the first director of the Museum. In 1852 the Cabinet with its library passed
under the aegis of the city of Trieste. In 1855 it was named City Museum of Natural History "Ferdinand Maximilian“, in
honour of the brother of Emperor Franz Joseph.
Mauro Rusconi
1776 – born in Pavia on 18th November
1796 – joins the Napoleonic army and enrols on the
Faculty of Medicine at the University of Pavia
1797 – commissioned into the artillery as a captain
at the stronghold of Mantova
1799 – goes back to Pavia to resume his studies as
Mantova is reoccupied by the Austrian army
1800 – the University of Pavia reopens at the return
of Napoleon
1806 – takes his degree in Medicine
1811 – becomes researcher and teaching assistant to
the chair of Physiology and Comparative Anatomy
1812 – shifts to Paris to attend Georges Cuvier’s
lessons of Comparative Anatomy
1813-19 – prosector to the chair of Physiology and
Comparative Anatomy at the University of Pavia
1819 – publishes a monograph on Proteus anguinus
1820 – refuses the chair of Universal Natural History
and Technology and loses every position at the
University
1821-47 – publishes studies on fertilization and development of amphibians and fish and the lymphatic
system of amphibians
1835-39 – publishes five letters to H. Weber to criticize von Baer’s embryological work
1849 – dies at Cadenabbia near Como on 27th March
With Prévost and Dumas (1824) we have the first accurate and
seriously analytical description of segmentation in the egg……the
manner in which von Baer dismissed this work and the work of
Mauro Rusconi seems to me to besmirch von Baer’s magisterial
reputation…
Prévost and Dumas were fully aware that the furrows that they
observed on the surface of the developing egg led to its complete
division…..To assert that Prévost and Dumas dealt only with
surface phenomena is, if one is charitable, a misreading of their
paper, or, if one is less so, a deliberate mis-representation of it.
There is no doubt whatever that Rusconi was fully aware of what
was going on…[he gave] a perfectly accurate description of
segmentation in the fertilized egg. It is therefore a matter of more
than a little surprise that von Baer in his notable paper on metamorphosis in the eggs of anurans summarily dismisses the earlier
work …in such a cavalier fashion….
Rusconi agrees with von Baer about the impossibility of ‘preformation’, but points out that the case against ‘preformation’ has
already been made by Prévost and Dumas.
von Baer’s paper was received by German scientists with acclaim,
and virtually all textbooks refer to him as the discoverer of the
biological significance of furrow formation and segmentation. The
true position appears to be that the discoverers were Prévost and
Dumas, and, with even greater clarity, Rusconi. The best that can
be said of von Baer’s paper is that he elaborated on their discovery and provided a great deal of additional experimental detail.
Annales des sciences naturelles, t.2;
1824
1826
Müllers Archiv für Anatomie, Physiologie
und wissenschaftliche Medizin, 1834
Rusconi
von Baer
According to Rusconi the unfertilized egg, coincident with the germ, is just a vesicle filled
with an amorphous fluid. Fertilization triggers an internal movement leading to a peculiar
type of crystallization which produces the elementary molecules of the major systems. The
furrows at the surface are due to the pressure of water and their number increases in relation to
the number of the inner dividing masses of the germ. When the furrows are obliterated the
germ appears to be transformed into a granular mass.
This crystallization could be called animalization, since fertilization endowes the germ with a
peculiar property which allowes him to pass from the liquid to the solid state and take gradually the animal form.
According to von Baer the egg is an organized entity standing in latent life. In the frog the
germinal layer is coincident with the pigmented cortex, which spreads all over the egg [during
gastrulation]. The furrows are nothing but the limits beween the dividing masses, which split
by dichotomous division. This division is brought about by a force acting from the surface
towards the inside, but it involves also the whole inner mass. Each dividing mass behaves as
an independent entity which, however, is still "part of the dominant unity". This subordination to the whole is revealed at first by the general pattern of division, but it is maintained
also in advanced stages. Divisions do not cease when the furrows are no more evident, but
they go on during the pause which precedes the embryo formation as well during the growth
of the embryo itself. "The self-divisions follow each other so long until the countless new
individualities have extremely less importance and appear to be only elementary parts of
a new individuum – the previous individuum will be dissolved by a vital process, albeit
without destroying him completely, and a novel one will be made by his fragments".
The view of Rusconi belongs to the antivitalistic attitude which dominated during the second
half of the XVIII century and tried to explain the properties of life with chemical and physical
laws. The elementary units of life were considered to be either particles (Maupertuis) or organic
molecules (Buffon) which aggregated by a process akin to crystal formation. However, Buffon
noticed that embryonic structures grow not only by addition of molecules at the surface, but in
three dimensions, as if they followed an "internal mould". Development, then, should occur by
aggregation as well as by inner modification.
The analogy between crystals and the elementary units of life (either fibres or globules or
"cells") was widely accepted during the first decades of the XIX century. In France it was
supported by Dutrochet and Raspail, who asserted that elementary vesicles or cells were produced by a crystallization sui generis, i.e. by a superimposition of molecules which led to saccular instead of angular shapes.
This model influenced Theodor Schwann, who is often considered to be the founder of the cell
theory together with Matthias J. Schleiden. However, these authors’ideas about the cells and
their origin were quite different from the current ones. As described by Schwann (1839), novel
cells arise inside a fluid called cytoblastema by a process of concentric addition. The nucleus is
formed around a previously formed nucleulus, and then, the cell is laid around the nucleus. This
exogenous formation of cells is comparable to the growth of crystals inside a solution, one
major difference being the addition of selected organic molecules between the previously existing ones (intussusception).
In comparison to these views, von Baer (1834) put forth a truly revolutionary idea:
"I consider the fragmentation of the yolk mass as the prototype of every histological
building. I do not believe that in the muscle elementary fibres settle near each other,
but that the previously formed ones go on to divide. The same occurs in the nervous
fibres".
Albrecht von Haller (1708-1777)
Further insight into the mechanism of cell division came from the studies von Baer carried out in
Italy (1845-46). In the semi-transparent sea urchin eggs he could observe that the nucleus was the
first to divide and the direction of its division determined the position of the cleavage plane
between the sister cells.
Contrary to the opinion of Schleiden, Schwann and other students, e.g. Albert von Kölliker who
in 1845 remarked that "nuclei and cells multiply by endogenous procreation", these observations
showed that every nucleus derives from a nucleus and a cell never formes either inside or
outside a previous cell.