THE BLOOD OF CHICK EMBRYOS
203
is still a considerable increase in primitive elements between the 4th and
6th day of incubation (Fig. 8).
(2) There is a gradual maturation of both the primitive and definitive
erythrocytes during incubation, with the exception of a temporary rise
in immature definitive red blood cells between the 12th and 14th day of
incubation (Dawson, 1936; Fennell, 1947; Sandreuter, 1951; Alexander
and Schjeide, 1953; Lemez, 1953). This rise has been associated by some
authors either with the onset of haemopoiesis in a new blood-forming
organ or with vigorous stimulation of the erythropoietic system. We
incline towards the latter view, in the sense that there is a great need of
erythrocytes during this period, which is reflected in the large daily
increments in the numbers of definitive erythrocytes in circulation
between the 11th and 13th day (more than one milliard per 24 hours).
In parallel with this many physiological and biochemical processes
accelerate about the 12th day of incubation. A slight increase in the
number of immature cells in circulation also occurred at the end of the
incubation period (Lemez, 1958), perhaps connected with the hatching
process ; it is interesting to compare this with the increase in less mature
granulocytes (Section II, C) and mitoses (Section II, F) in the circulatory
system during this period.
(3) The embryonic definitive erythrocytes (Ε II) are not all alike
during the incubation period. At the 7th day of incubation most of them
possess a round nucleus, instead of the oval or oblong nucleus which is
characteristic of definitive erythrocytes in the second half of the
incubation period and in adult birds. The elements with round nuclei
were designated by Lemez (1953) as definitive erythrocyte type Ε
and the others as type Ε II 2 (Fig. ΙΑ, B). In size, the cells of the two
types are equal (Lemez, 1953). This morphological peculiarity did
not escape the attention of Dantschakoff (1908a) and Price-Jones
(1910). Up to the 12th day Fennell (1947) gave only one value (diameters)
to express the dimensions of the nucleus of definitive erythrocytes ; for
the subsequent period two dimensions (length and width) are given.
Keller (1933) explicitly held that definitive erythrocytes with round
nuclei were immature stages of those with oval or oblong nuclei; in
general the same opinion is held by the other investigators mentioned.
In our opinion the problem of the mutual relations of erythrocytes
type Ε II X and Ε II 2 was solved by means of the reticulocyte differential
count (Lemez, 1953).
A gradual maturation of reticulocytes of the primitive line was
recorded by Doan et al. (1925). Sugiyama (1926), Dawson (1936), and
Fennell (1947) also remarked on the occurrence of immature erythrocytes
in chick embryos and the appearance of the so called granulo-filamentous
substance in their cytoplasm in the later period of incubation, but no
203
is still a considerable increase in primitive elements between the 4th and
6th day of incubation (Fig. 8).
(2) There is a gradual maturation of both the primitive and definitive
erythrocytes during incubation, with the exception of a temporary rise
in immature definitive red blood cells between the 12th and 14th day of
incubation (Dawson, 1936; Fennell, 1947; Sandreuter, 1951; Alexander
and Schjeide, 1953; Lemez, 1953). This rise has been associated by some
authors either with the onset of haemopoiesis in a new blood-forming
organ or with vigorous stimulation of the erythropoietic system. We
incline towards the latter view, in the sense that there is a great need of
erythrocytes during this period, which is reflected in the large daily
increments in the numbers of definitive erythrocytes in circulation
between the 11th and 13th day (more than one milliard per 24 hours).
In parallel with this many physiological and biochemical processes
accelerate about the 12th day of incubation. A slight increase in the
number of immature cells in circulation also occurred at the end of the
incubation period (Lemez, 1958), perhaps connected with the hatching
process ; it is interesting to compare this with the increase in less mature
granulocytes (Section II, C) and mitoses (Section II, F) in the circulatory
system during this period.
(3) The embryonic definitive erythrocytes (Ε II) are not all alike
during the incubation period. At the 7th day of incubation most of them
possess a round nucleus, instead of the oval or oblong nucleus which is
characteristic of definitive erythrocytes in the second half of the
incubation period and in adult birds. The elements with round nuclei
were designated by Lemez (1953) as definitive erythrocyte type Ε
and the others as type Ε II 2 (Fig. ΙΑ, B). In size, the cells of the two
types are equal (Lemez, 1953). This morphological peculiarity did
not escape the attention of Dantschakoff (1908a) and Price-Jones
(1910). Up to the 12th day Fennell (1947) gave only one value (diameters)
to express the dimensions of the nucleus of definitive erythrocytes ; for
the subsequent period two dimensions (length and width) are given.
Keller (1933) explicitly held that definitive erythrocytes with round
nuclei were immature stages of those with oval or oblong nuclei; in
general the same opinion is held by the other investigators mentioned.
In our opinion the problem of the mutual relations of erythrocytes
type Ε II X and Ε II 2 was solved by means of the reticulocyte differential
count (Lemez, 1953).
A gradual maturation of reticulocytes of the primitive line was
recorded by Doan et al. (1925). Sugiyama (1926), Dawson (1936), and
Fennell (1947) also remarked on the occurrence of immature erythrocytes
in chick embryos and the appearance of the so called granulo-filamentous
substance in their cytoplasm in the later period of incubation, but no