A. Weissmann and other authors. According to his opinion “the clue to the
solution of fertilization was lying in stereochemistry”.
The biological role of nuclein has begun to become clearer due to the
studies of a number of biologists and cytologists — O. Hertwig, W. Flemming,
E. van Beneden, etc. They have observed the penetration of spermatozoa in
eggs of various animal species (mainly sea urchin and sea star) after which
their nuclei have fused. A great interest was provoked by the thread-like
formations in the nuclei later called chromosomes (Greek: chroma — colour
and soma — body). Yet at that time Hertwig (1875) has arrived at the
conclusion that the chromosome number is doubled in the fertilization, and
Flemming (1880) has surmised that after the division of the chromosomes
along their axis each half goes to one of the daughter cells. In two years time
Flemming (1882) has described a division of epithelial cells from salamander
in which the chromosomes are clearly outlined. He has suggested the term
mitosis and has reached to the conclusion about the constant chromosome
number in the cells of a given species. Van Beneden (1883 b) has described
fertilization and division of cells in the parasitic round worms Ascaris. This
subject of study has proved very convenient since by contrast to other ones, it
has only two chromosomes in the nuclei of sexual cells which allows for the
easy observation under the light microscope. In this work of his van Beneden
has for the first time described meiosis — the reduction of the chromosome
number by half as opposed to the process of fertilization. Up till then the role of
the nucleus has remained unclear although it was already discovered. This
essential problem connected to the discovery of cell division will be later
treated again in Chapter 3 (Section 3. 2).
Nuclein has been actively occupying researchers minds. Cytological
studies in vitro as well as after fixation and staining of the cells have shown
a zone of a dense matter in the nucleus called chromatin. It was later that
the notion has arisen that in the process of division the maximally
condensed chromatin is shaped as chromosomes. At that time the giant
(polythene) chromosomes have been discovered in the salivary glands of
Chironomus (Balbiani, 1881), as well as the lampbrush type chromosomes
in oocytes of Siredon (Flemming, 1882). The idea has cropped up that
nuclein was the hereditary material in the observed chromosomes. In 1895
the American cytologist E. B. Wilson has assumed that nuclein is very
similar if not identical to the substance called chromatin. It has proven
however, that the quantity of chromatin varies with the timing of the cell
division cycle and the physiological state of the cells. In 1909 the German
botanist E. Strasburger has expressed his opinion that chromatin cannot
serve as hereditary material, since its content is considerably changing in
the process of cell development. This view of Strasburger was adopted by
Wilson and in the third edition of his book “The Cell in Development and
Heredity” (Wilson, 1925) he has stated that “individuality of organisms and