THE BLOOD OF CHICK EMBRYOS
225
mitotic activity in primitive erythrocytes is closely followed by decreasing oxygen consumption (O'Connor, 1951, 1952a) between the 2nd and
8th day of incubation. The subsequent overall decline in oxygen
consumption (Leibsohn, 1940; Boyer, 1950) is in parallel with the
decrease in the reticulocyte index (Lemez, 1953).
The mitotic activity in precirculation stages (before 40 hours of
incubation) takes place in the so-called blood islands. Sabin (1920)
described the intravascularly situated youngest blood cells as forming a
syncytium, but recently Houser et al. (1961), with the help of phase
contrast microscopy, demonstrated that the cell boundaries of primitive
red blood cells in the blood islands are always distinguishable. Because
all cells of one blood island enter mitosis simultaneously (Sabin, 1920),
there is always an accumulation of certain mitotic phases in blood
smears from the 30-hour-old blastoderm (Astaldi et al., 1953). Later,
from the 2nd till the 5th day, when mitoses are still numerous, the ratio
of the four phases of the mitotic cycle remains quite constant (Astaldi
et al., 1953; Lemez and Rychter, 1956, 1958a) even at 12-hour intervals
(Astaldi et al., 1953). This may be taken as proof of a random distribution
of mitoses in the circulation and of the absence of mitotic waves, e.g., of
a diurnal cycle.
Dehler (1895) was probably the first to describe spheres, that were in
his time regarded as specific for leucocytes, in chick embryo primitive
erythroblasts. The changes in the position of the chondriosome during
mitosis of primitive erythrocytes were described by Takagi (1932). The
course of mitoses of primitive red blood cells in vitro was followed by
Rondanelli et al. (1955a, b). By phase contrast microcinematography
Rondanelli et al. (1956) demonstrated that the 'bubbling' of the cell
surface, observed during telophase in mesenchymal and fibroblastic
cells cultivated in vitro, is absent during cytodiaresis in chick embryo
haemopoietic cells. This is correlated with a more advanced cellular
differentiation in the latter.
Mitoses of definitive basophilic proerythroblasts (haemocytoblasts)
(Ε II) were observed on the 4th day. The course of the mitotic index was
determined for the definitive line by Dawson (1936) and Astaldi et al.
(1952) starting with the 5th day. The initial values are relatively high
(2-2 and 3-8%) diminishing rapidly according to Dawson and slowly
according to the other group, ceasing practically completely by the 9th
day in both studies. From the 10th day onwards the frequency of
definitive red blood cell mitosis is about 1: 100,000 being slightly higher
at the end of the incubation period (Lemez, unpublished).
Thromboblast mitosis between the 2nd and 5th day of incubation is
very rare, but it has been observed (Lemez, unpublished). These mitoses
exhibit a very faint bluish plasma, the chromosomes being violet in colour.
225
mitotic activity in primitive erythrocytes is closely followed by decreasing oxygen consumption (O'Connor, 1951, 1952a) between the 2nd and
8th day of incubation. The subsequent overall decline in oxygen
consumption (Leibsohn, 1940; Boyer, 1950) is in parallel with the
decrease in the reticulocyte index (Lemez, 1953).
The mitotic activity in precirculation stages (before 40 hours of
incubation) takes place in the so-called blood islands. Sabin (1920)
described the intravascularly situated youngest blood cells as forming a
syncytium, but recently Houser et al. (1961), with the help of phase
contrast microscopy, demonstrated that the cell boundaries of primitive
red blood cells in the blood islands are always distinguishable. Because
all cells of one blood island enter mitosis simultaneously (Sabin, 1920),
there is always an accumulation of certain mitotic phases in blood
smears from the 30-hour-old blastoderm (Astaldi et al., 1953). Later,
from the 2nd till the 5th day, when mitoses are still numerous, the ratio
of the four phases of the mitotic cycle remains quite constant (Astaldi
et al., 1953; Lemez and Rychter, 1956, 1958a) even at 12-hour intervals
(Astaldi et al., 1953). This may be taken as proof of a random distribution
of mitoses in the circulation and of the absence of mitotic waves, e.g., of
a diurnal cycle.
Dehler (1895) was probably the first to describe spheres, that were in
his time regarded as specific for leucocytes, in chick embryo primitive
erythroblasts. The changes in the position of the chondriosome during
mitosis of primitive erythrocytes were described by Takagi (1932). The
course of mitoses of primitive red blood cells in vitro was followed by
Rondanelli et al. (1955a, b). By phase contrast microcinematography
Rondanelli et al. (1956) demonstrated that the 'bubbling' of the cell
surface, observed during telophase in mesenchymal and fibroblastic
cells cultivated in vitro, is absent during cytodiaresis in chick embryo
haemopoietic cells. This is correlated with a more advanced cellular
differentiation in the latter.
Mitoses of definitive basophilic proerythroblasts (haemocytoblasts)
(Ε II) were observed on the 4th day. The course of the mitotic index was
determined for the definitive line by Dawson (1936) and Astaldi et al.
(1952) starting with the 5th day. The initial values are relatively high
(2-2 and 3-8%) diminishing rapidly according to Dawson and slowly
according to the other group, ceasing practically completely by the 9th
day in both studies. From the 10th day onwards the frequency of
definitive red blood cell mitosis is about 1: 100,000 being slightly higher
at the end of the incubation period (Lemez, unpublished).
Thromboblast mitosis between the 2nd and 5th day of incubation is
very rare, but it has been observed (Lemez, unpublished). These mitoses
exhibit a very faint bluish plasma, the chromosomes being violet in colour.