1. INTRODUCTION
5
Lamarck, the studies performed by Cuvier and his disciples demonstrated a scale of animals in growing complexity of their organization.
For him, the resemblances were the effects of a genetic derivation and
not, as they were for Cuvier, evidence of a community of nature.
The "unity of plan" dear to Goethe and to Geoffrey St.-Hilaire was
a purely philosophical concept. It was not the only endeavor to define
organic unity. To this natural question in the human mind, a scientific
answer was given by the cell theory as formulated by Theodor
Schwann in 1839. As this theory remained the basis of organic unity
until the present time, it is worthwhile to examine how comparative
studies brought it about. The search for a common principle of organization had been the aim of micrographers for some time. In the
eighteenth century, the unit was the "fiber." Later on came the "globulists" such as Fontana, Wenzel, Dutrochet, Raspail, and Purkinje. The
notion of "globule" included quite a variety of structures: grains, nuclei,
as well as optical illusions, but occasionally the "globulists" came across
a real cell. The botanists were first to realize that plants were exclusively made of cells but at the time that Schwann wrote his epochmaking book, the general opinion was that the growth of animals essentially differs from the growth of plants. According to ideas then current,
the presence of blood vessels was characteristic of animals and determined their mode of growth. This concept gave way to the theory proposed by Schwann, according to which all organisms are formed by
anatomical elements derived from cells, and are cells, differentiated
cells, or the products of cell activity. The original and valuable contribution of Schwann was to show the formation of all tissues by cell
differentiation; his theory in which he adheres to Schleiden's principle
that cells are produced in an unorganized medium has long been proved
to be wrong. The theory that cells are produced by the division of preexisting cells resulted from three lines of research: the observation by
Trembley, Ch. Morren, Ehrenberg, etc. of the multiplication of Protista;
the observation by Dumortier, Mohl, Meyen, and others of cell multiplication in Algae; and the observation by Prevost and Dumas, by von
Siebold, by Bary, and by others, of the development of the egg.
But it was Robert Remak, a student of Johannes Müller, who generalized and clearly described the notion of cell multiplication by division of pre-existing cells, a concept which was popularized and applied to pathological growth by Rud. Virchow. The cell theory is not a
philosophical theory. If it is true that Schwann, who tried to oppose the
point of view of the physicist to that of the Naturphilosophen, found
the very principle of unity which had been one of the objectives of
Naturphilosophie, his main scientific discovery, brought about by his
5
Lamarck, the studies performed by Cuvier and his disciples demonstrated a scale of animals in growing complexity of their organization.
For him, the resemblances were the effects of a genetic derivation and
not, as they were for Cuvier, evidence of a community of nature.
The "unity of plan" dear to Goethe and to Geoffrey St.-Hilaire was
a purely philosophical concept. It was not the only endeavor to define
organic unity. To this natural question in the human mind, a scientific
answer was given by the cell theory as formulated by Theodor
Schwann in 1839. As this theory remained the basis of organic unity
until the present time, it is worthwhile to examine how comparative
studies brought it about. The search for a common principle of organization had been the aim of micrographers for some time. In the
eighteenth century, the unit was the "fiber." Later on came the "globulists" such as Fontana, Wenzel, Dutrochet, Raspail, and Purkinje. The
notion of "globule" included quite a variety of structures: grains, nuclei,
as well as optical illusions, but occasionally the "globulists" came across
a real cell. The botanists were first to realize that plants were exclusively made of cells but at the time that Schwann wrote his epochmaking book, the general opinion was that the growth of animals essentially differs from the growth of plants. According to ideas then current,
the presence of blood vessels was characteristic of animals and determined their mode of growth. This concept gave way to the theory proposed by Schwann, according to which all organisms are formed by
anatomical elements derived from cells, and are cells, differentiated
cells, or the products of cell activity. The original and valuable contribution of Schwann was to show the formation of all tissues by cell
differentiation; his theory in which he adheres to Schleiden's principle
that cells are produced in an unorganized medium has long been proved
to be wrong. The theory that cells are produced by the division of preexisting cells resulted from three lines of research: the observation by
Trembley, Ch. Morren, Ehrenberg, etc. of the multiplication of Protista;
the observation by Dumortier, Mohl, Meyen, and others of cell multiplication in Algae; and the observation by Prevost and Dumas, by von
Siebold, by Bary, and by others, of the development of the egg.
But it was Robert Remak, a student of Johannes Müller, who generalized and clearly described the notion of cell multiplication by division of pre-existing cells, a concept which was popularized and applied to pathological growth by Rud. Virchow. The cell theory is not a
philosophical theory. If it is true that Schwann, who tried to oppose the
point of view of the physicist to that of the Naturphilosophen, found
the very principle of unity which had been one of the objectives of
Naturphilosophie, his main scientific discovery, brought about by his