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LEO LEME2
Β. Thrombocytes
The second cellular component to appear in the chick embryo
circulatory system are the thrombocytes which in contrast to mammalian
platelets are true cells. They have been the most controversial blood
component in adults and embryos, both as to their origin in general and
as to the time of their appearance in the embryo in particular. Many
papers which thoroughly describe chick embryo erythrocytes and
leucocytes do not mention thrombocytes at all.
The thrombocytes of hens are oval cells, smaller than erythrocytes
(6x9 μ,), with pale, often damaged, cytoplasm containing one or two
azurophilic granules. The nucleus, too, is oval (5 χ 3-5 μ) and stains more
deeply than that of erythrocytes. In origin, they have repeatedly been
claimed to be either the remains of erythrocyte nuclei with a narrow
cytoplasmic rim (especially in embryos, e.g., Price-Jones, 1910; Tûma,
1923, 1924; Fennell, 1947) or to be erythrocytes in which the process of
haemoglobinization of the cell has not proceeded to maturity (Gordon,
1926; Blount, 1939b). The only similarity between erythrocytes and
thrombocytes in hens is the fact that both, as opposed to white blood
cells, differentiate intravascularly (Dantschakoff, 1909; Jordan, 1936).
At least for the thrombocytes of adult hens, the problem was solved
by the immunological investigations of Rosenthal and Falkenheim
(1922) and of Ledingham and Woodecock (quoted by Firket, 1925) who
showed that there is no immunological relation between erythrocytes
and thrombocytes, while there may be a slight one between leucocytes
(lymphocytes) and thrombocytes. However, the morphologists have not
taken these observations into account.
In embryos, thrombocytes were illustrated as early as 1858 by Remak
who called them 'sehr kleine gefärbte kernhaltige Zellen'. Engel (1895)
called them lymphocytes. Dantschakoff (1908a) observed them first at
54 hours of incubation (Sugiyama (1926) at the 20-30 somite stage) and
designated them as 'Microblasten' and 'Microcyten', recognizing them
as a separate cell line unrelated to erythrocytes. (The latter must be
distinguished from nuclear remnants of erythrocytes possessing a
narrow cytoplasmic rim.) Later Dantschakoff (1909) named these cells
thromboblasts and thrombocytes. Their stem cell—the thromboblast—
is very similar to lymphocytes in cell size and to haemocytoblasts in the
deeply bluish staining cytoplasm and nuclear pattern ; the cytoplasm of
the thromboblasts, however, often forms bubble-like extensions, which
may eventually become detached in smears.
Thromboblasts may be found in blood smears up to the 5th day of
incubation (Sugiyama, 1926; Lojda and Lemez, 1955). But on the 3rd
day, more or less mature thrombocytes are a regular component of the
LEO LEME2
Β. Thrombocytes
The second cellular component to appear in the chick embryo
circulatory system are the thrombocytes which in contrast to mammalian
platelets are true cells. They have been the most controversial blood
component in adults and embryos, both as to their origin in general and
as to the time of their appearance in the embryo in particular. Many
papers which thoroughly describe chick embryo erythrocytes and
leucocytes do not mention thrombocytes at all.
The thrombocytes of hens are oval cells, smaller than erythrocytes
(6x9 μ,), with pale, often damaged, cytoplasm containing one or two
azurophilic granules. The nucleus, too, is oval (5 χ 3-5 μ) and stains more
deeply than that of erythrocytes. In origin, they have repeatedly been
claimed to be either the remains of erythrocyte nuclei with a narrow
cytoplasmic rim (especially in embryos, e.g., Price-Jones, 1910; Tûma,
1923, 1924; Fennell, 1947) or to be erythrocytes in which the process of
haemoglobinization of the cell has not proceeded to maturity (Gordon,
1926; Blount, 1939b). The only similarity between erythrocytes and
thrombocytes in hens is the fact that both, as opposed to white blood
cells, differentiate intravascularly (Dantschakoff, 1909; Jordan, 1936).
At least for the thrombocytes of adult hens, the problem was solved
by the immunological investigations of Rosenthal and Falkenheim
(1922) and of Ledingham and Woodecock (quoted by Firket, 1925) who
showed that there is no immunological relation between erythrocytes
and thrombocytes, while there may be a slight one between leucocytes
(lymphocytes) and thrombocytes. However, the morphologists have not
taken these observations into account.
In embryos, thrombocytes were illustrated as early as 1858 by Remak
who called them 'sehr kleine gefärbte kernhaltige Zellen'. Engel (1895)
called them lymphocytes. Dantschakoff (1908a) observed them first at
54 hours of incubation (Sugiyama (1926) at the 20-30 somite stage) and
designated them as 'Microblasten' and 'Microcyten', recognizing them
as a separate cell line unrelated to erythrocytes. (The latter must be
distinguished from nuclear remnants of erythrocytes possessing a
narrow cytoplasmic rim.) Later Dantschakoff (1909) named these cells
thromboblasts and thrombocytes. Their stem cell—the thromboblast—
is very similar to lymphocytes in cell size and to haemocytoblasts in the
deeply bluish staining cytoplasm and nuclear pattern ; the cytoplasm of
the thromboblasts, however, often forms bubble-like extensions, which
may eventually become detached in smears.
Thromboblasts may be found in blood smears up to the 5th day of
incubation (Sugiyama, 1926; Lojda and Lemez, 1955). But on the 3rd
day, more or less mature thrombocytes are a regular component of the