THE BLOOD OF CHICK EMBRYOS
229
(1895). Dawson (1936) was the first to recognize clearly that the relative
reduction in numbers of primitive erythrocytes could be explained
either by their extinction, because they show degenerative changes at
an early stage and there is presumably little production of Ε I beyond
the 5th day of incubation, or by their dilution, because there is an
18-fold increase in the embryo + membrane weight between the 6th and
18th day of incubation, and there must be a close correlation between
increase in blood volume and in weight. Dawson left the problem open,
for no data were then available on circulating blood volume. The
estimation of the circulating blood volume throughout the incubation
period by Rychter et al. (1955a, b) was undertaken primarily in order to
answer this question.
1. Maximal and Average Life Span of Primitive Erythrocytes (Ε I)
The maximal life span in this case is the time interval from the onset
of circulation (at about 40 hours of incubation, about 2 days) to that
stage of ontogenesis when no primitive erythrocytes are found in blood
smears. The maximal life span was reported variously to be 20 days
(Engel, 1895), 23 days (Price-Jones, 1910), 34 days (Dawson, 1936), and
28 days (Sandreuter, 1951). The last two authors regarded all erythroplastids as belonging to the primitive line and thus as persisting Ε I
elements. Lemez and Rychter (1956) reported a maximal life span of
22 days, because on the 4th postembryonic day not a single primitive
erythrocyte was present among a total of 600,000 erythrocytes studied
in twelve individual blood smears (Fig. 8).
The average life span of primitive erythrocytes was calculated from
their survival curve (Fig. 8) constructed from the total erythrocyte
number in circulation from the 2nd day of incubation to the 1st
postembryonic day (Fig. 10A) (obtained by multiplication of the blood
volume values (Fig. 6A) and the corresponding erythrocyte number per
cu.mm (Fig. 2B) every day of development) and from the erythrocyte
differential count (Lemez and Rychter, 1956). The total number of
primitive erythrocytes is one million on the 2nd day of development,
and the maximal value—108-6 million—is reached on the 6th day;
thereafter their number decreases regularly by some 10 million a day up
to about the 17th day; on the 1st postembryonic day only 150,000 are
present, that is about l*5°/ 00 of the maximal value (Fig. 8). The average
life span of Ε I calculated from this survival curve is 8-1 days. Taking
into account that some of them divided during circulation, this value
could be extended to 8-5 days at most. These numbers are valid only if
no primitive erythrocytes are destroyed before the 6th day of incubation
and none enter the circulation after this stage. Each of these two possibilities would cause a cryptogenic turnover which would, however,
229
(1895). Dawson (1936) was the first to recognize clearly that the relative
reduction in numbers of primitive erythrocytes could be explained
either by their extinction, because they show degenerative changes at
an early stage and there is presumably little production of Ε I beyond
the 5th day of incubation, or by their dilution, because there is an
18-fold increase in the embryo + membrane weight between the 6th and
18th day of incubation, and there must be a close correlation between
increase in blood volume and in weight. Dawson left the problem open,
for no data were then available on circulating blood volume. The
estimation of the circulating blood volume throughout the incubation
period by Rychter et al. (1955a, b) was undertaken primarily in order to
answer this question.
1. Maximal and Average Life Span of Primitive Erythrocytes (Ε I)
The maximal life span in this case is the time interval from the onset
of circulation (at about 40 hours of incubation, about 2 days) to that
stage of ontogenesis when no primitive erythrocytes are found in blood
smears. The maximal life span was reported variously to be 20 days
(Engel, 1895), 23 days (Price-Jones, 1910), 34 days (Dawson, 1936), and
28 days (Sandreuter, 1951). The last two authors regarded all erythroplastids as belonging to the primitive line and thus as persisting Ε I
elements. Lemez and Rychter (1956) reported a maximal life span of
22 days, because on the 4th postembryonic day not a single primitive
erythrocyte was present among a total of 600,000 erythrocytes studied
in twelve individual blood smears (Fig. 8).
The average life span of primitive erythrocytes was calculated from
their survival curve (Fig. 8) constructed from the total erythrocyte
number in circulation from the 2nd day of incubation to the 1st
postembryonic day (Fig. 10A) (obtained by multiplication of the blood
volume values (Fig. 6A) and the corresponding erythrocyte number per
cu.mm (Fig. 2B) every day of development) and from the erythrocyte
differential count (Lemez and Rychter, 1956). The total number of
primitive erythrocytes is one million on the 2nd day of development,
and the maximal value—108-6 million—is reached on the 6th day;
thereafter their number decreases regularly by some 10 million a day up
to about the 17th day; on the 1st postembryonic day only 150,000 are
present, that is about l*5°/ 00 of the maximal value (Fig. 8). The average
life span of Ε I calculated from this survival curve is 8-1 days. Taking
into account that some of them divided during circulation, this value
could be extended to 8-5 days at most. These numbers are valid only if
no primitive erythrocytes are destroyed before the 6th day of incubation
and none enter the circulation after this stage. Each of these two possibilities would cause a cryptogenic turnover which would, however,