THE BLOOD OF CHICK EMBRYOS
227
nucleus, especially in the latter instance, so that these early blood
island divisions seem to be analogous to egg cleavage, where a lot of
DNA precursors are available.
3. Mitotic Time and Productivity of Primitive
Erythrocyte
Mitoses in Circulation
Unfortunately the mitotic index alone cannot really express cell
productivity, which depends not only on the frequency of mitosis
(mitotic index) but also on the duration of mitosis (mitotic time).
Using the colchicine technique, Lemez and Rychter (1956, 1958a)
demonstrated that gradual maturation of primitive erythrocytes
between the 2nd and 5th days of incubation is accompanied by a
lengthening of the average mitotic time from 52 to 88 minutes (the
value of 174-5 minutes on the 6th day is not too reliable because of the
low mitotic and low stathmokinetic indices) with a plateau between
the 3rd and 4th day (Fig. 7—T). The value of 52 minutes on the 2nd day
is in good agreement with the finding of Sabin (1920) that mitosis in the
blood island in a young explanted blastoderm lasts about 1 hour.
The significance of the changing mitotic time during development in
quantitative calculations at the cellular level has been proved for cells
in the spinal cord of chick embryos by Jelinek (1961). The mitotic time
from the 2nd till the 6th day of incubation was found to increase from
23 to 149 minutes (Jelinek, 1959).
The question of the role of mitoses in the circulatory system in the
total proliferation of the primitive erythrocytes (Ε I) can now be settled.
They are poured into circulation from the erythropoietic loci of the yolk
sac wall and simultaneously they proliferate by mitoses in the circulatory
system. The former mode of their increase may be considered as immigration, if the circulating Ε I are regarded as the basic set.
Assuming that there are no primitive erythrocyte deaths till the 6th
day of incubation and no other forms of Ε I proliferation but mitosis
and immigration, or that cell deaths and cell fragmentations are
negligible, then the total count is based on the total number of primitive
erythrocytes in circulation between the 2nd and the 6th day (Fig. 8)
and the corresponding mitotic indices and mitotic times (Fig. 7). There
are at least 3 possible ways of calculating cell productivity due to
mitoses from the above data (for discussion see Lemez and Josifko,
1957). The most general procedure is to calculate the ratio of the actual
(measured) mitotic time and of the calculated one (on the assumption
that at the given mitotic index the mitotic activity alone—without
immigration—is responsible for the entire increase in primitive erythrocyte number) every day from the 2nd till the 6th day of incubation. It is
227
nucleus, especially in the latter instance, so that these early blood
island divisions seem to be analogous to egg cleavage, where a lot of
DNA precursors are available.
3. Mitotic Time and Productivity of Primitive
Erythrocyte
Mitoses in Circulation
Unfortunately the mitotic index alone cannot really express cell
productivity, which depends not only on the frequency of mitosis
(mitotic index) but also on the duration of mitosis (mitotic time).
Using the colchicine technique, Lemez and Rychter (1956, 1958a)
demonstrated that gradual maturation of primitive erythrocytes
between the 2nd and 5th days of incubation is accompanied by a
lengthening of the average mitotic time from 52 to 88 minutes (the
value of 174-5 minutes on the 6th day is not too reliable because of the
low mitotic and low stathmokinetic indices) with a plateau between
the 3rd and 4th day (Fig. 7—T). The value of 52 minutes on the 2nd day
is in good agreement with the finding of Sabin (1920) that mitosis in the
blood island in a young explanted blastoderm lasts about 1 hour.
The significance of the changing mitotic time during development in
quantitative calculations at the cellular level has been proved for cells
in the spinal cord of chick embryos by Jelinek (1961). The mitotic time
from the 2nd till the 6th day of incubation was found to increase from
23 to 149 minutes (Jelinek, 1959).
The question of the role of mitoses in the circulatory system in the
total proliferation of the primitive erythrocytes (Ε I) can now be settled.
They are poured into circulation from the erythropoietic loci of the yolk
sac wall and simultaneously they proliferate by mitoses in the circulatory
system. The former mode of their increase may be considered as immigration, if the circulating Ε I are regarded as the basic set.
Assuming that there are no primitive erythrocyte deaths till the 6th
day of incubation and no other forms of Ε I proliferation but mitosis
and immigration, or that cell deaths and cell fragmentations are
negligible, then the total count is based on the total number of primitive
erythrocytes in circulation between the 2nd and the 6th day (Fig. 8)
and the corresponding mitotic indices and mitotic times (Fig. 7). There
are at least 3 possible ways of calculating cell productivity due to
mitoses from the above data (for discussion see Lemez and Josifko,
1957). The most general procedure is to calculate the ratio of the actual
(measured) mitotic time and of the calculated one (on the assumption
that at the given mitotic index the mitotic activity alone—without
immigration—is responsible for the entire increase in primitive erythrocyte number) every day from the 2nd till the 6th day of incubation. It is