THE BLOOD OF CHICK EMBRYOS
235
There are, however, data in the literature supporting a high rate of
erythrocyte destruction towards the end of incubation, which cannot be
caused solely by destruction of Ε I and Ε II X erythrocytes, because most
of them disappeared at earlier stages of development, as shown by their
survival curves. The findings of Ramsay (1951) indicate that there is a
great accumulation of iron in chick embryo liver originating from
destroyed erythrocytes after the 17th day of incubation. A great
accumulation of bile pigments towards the end of the incubation period
was reported by Sendju (1927) and was presumed by many others. The
total number of erythrocytes destroyed during the incubation period
could be estimated biochemically, therefore, either from the total bile
pigment production or by determination of the amount of iron released
from destroyed erythrocytes. It is possible that no turnover of either
substance occurs. Both methods would, of course, estimate only the
breakdown of more or less mature erythrocytes, because young forms
contain very little haemoglobin and, consequently, very little iron.
The erythrocyte balance sheet from the 2nd day of development to
the 1st day after hatching is given in Table I. It is apparent that about
5-4 milliards out of 12-7 milliards are destroyed during this period. This
indicates that about 40% of erythrocytes produced are used for renewal
and about 60% to cover the needs of the developing chick. The ratio of
the total numbers of Ε I : Ε II X : ΕII 2 produced during prenatal development is of the order 1: 10: 100 (Table I).
Finally, some remarks on the fate of embryonic erythrocytes after
hatching. From quantitative data on erythropoiesis in the femoral and
tibial bone marrow in chicks after hatching (Burmester et al., 1941), it
emerges that the blood-forming tissue present in these long bones (that
in the vertebrae, etc., is not included) secures a daily production of more
than 1 milliard erythrocytes per day after the 3rd postembryonic day,
on the assumption that differentiation of a young erythrocyte lasts a
little more than 3 days. This value is acceptable for both the embryonic
erythrocytes (Lemez, 1953—reticulocyte counts) and adult erythrocytes
(3·2-3·6 days, Ottesen, 1955). From the day of hatching to the 6th day
afterwards, the number of red cells in the bone marrow of the four long
bones increases 11 times, whereas the body weight increases only by
half during the same period (Burmester et al., 1941). Simultaneously
there is a decrease in erythrocyte number from 2-9 to 2-5 million per
cu.mm (Burmester et al., 1941 ; Sandreuter, 1951 ; Lemez, unpublished).
An exchange of embryonic erythrocytes after hatching is indicated also
by their diminishing size, which sets in immediately after hatching
(Sandreuter, 1951), and is revealed also by the fall in the haematocrit
value on the 1st day after hatching (Rychter et al., 1955a).
It is most probable that the 7-3 milliards of embryonic erythrocytes
235
There are, however, data in the literature supporting a high rate of
erythrocyte destruction towards the end of incubation, which cannot be
caused solely by destruction of Ε I and Ε II X erythrocytes, because most
of them disappeared at earlier stages of development, as shown by their
survival curves. The findings of Ramsay (1951) indicate that there is a
great accumulation of iron in chick embryo liver originating from
destroyed erythrocytes after the 17th day of incubation. A great
accumulation of bile pigments towards the end of the incubation period
was reported by Sendju (1927) and was presumed by many others. The
total number of erythrocytes destroyed during the incubation period
could be estimated biochemically, therefore, either from the total bile
pigment production or by determination of the amount of iron released
from destroyed erythrocytes. It is possible that no turnover of either
substance occurs. Both methods would, of course, estimate only the
breakdown of more or less mature erythrocytes, because young forms
contain very little haemoglobin and, consequently, very little iron.
The erythrocyte balance sheet from the 2nd day of development to
the 1st day after hatching is given in Table I. It is apparent that about
5-4 milliards out of 12-7 milliards are destroyed during this period. This
indicates that about 40% of erythrocytes produced are used for renewal
and about 60% to cover the needs of the developing chick. The ratio of
the total numbers of Ε I : Ε II X : ΕII 2 produced during prenatal development is of the order 1: 10: 100 (Table I).
Finally, some remarks on the fate of embryonic erythrocytes after
hatching. From quantitative data on erythropoiesis in the femoral and
tibial bone marrow in chicks after hatching (Burmester et al., 1941), it
emerges that the blood-forming tissue present in these long bones (that
in the vertebrae, etc., is not included) secures a daily production of more
than 1 milliard erythrocytes per day after the 3rd postembryonic day,
on the assumption that differentiation of a young erythrocyte lasts a
little more than 3 days. This value is acceptable for both the embryonic
erythrocytes (Lemez, 1953—reticulocyte counts) and adult erythrocytes
(3·2-3·6 days, Ottesen, 1955). From the day of hatching to the 6th day
afterwards, the number of red cells in the bone marrow of the four long
bones increases 11 times, whereas the body weight increases only by
half during the same period (Burmester et al., 1941). Simultaneously
there is a decrease in erythrocyte number from 2-9 to 2-5 million per
cu.mm (Burmester et al., 1941 ; Sandreuter, 1951 ; Lemez, unpublished).
An exchange of embryonic erythrocytes after hatching is indicated also
by their diminishing size, which sets in immediately after hatching
(Sandreuter, 1951), and is revealed also by the fall in the haematocrit
value on the 1st day after hatching (Rychter et al., 1955a).
It is most probable that the 7-3 milliards of embryonic erythrocytes