232
LEO
LEME2
of embryonal Ε I and Ε IIj erythrocytes was estimated to be below
14,000, less than 10% of the adult values (Lemez and Rychter, 1961).
The high degree of immaturity observed in both lines of embryonic
erythrocytes released into circulation, according to reticulocyte counts
(Lemez, 1953), seems to be the most important factor concerned in
shortening the life span. Considerable shortening of the average life
span of erythrocytes in the rabbit (Neuberger and Niven, 1951) and in
the rat (Berlin and Lötz, 1951), from 67 to 43 days and from 64 to 27
days, respectively, was reported after extensive bleeding compensated
by the release of large numbers of immature erythrocytes (reticulocytes)
into circulation. Further, the high metabolic rate in embryos might
have some effect on life span. Brace (1953) found a considerable
prolongation of the average erythrocyte life span in a hibernating
marmot. Rodnan et al. (1957) demonstrated that the life span of erythrocytes in mammals, birds and reptiles correlates directly with basal heat
production per kilogramme body weight.
H. Balance Sheet of Erythrocyte Production and Destruction
throughout the Incubation Period
Data collected in previous parts of this section make it possible to
strike a balance between red blood cell production and destruction from
the 2nd day of development till the 1st postembryonic day (Table I, and
Figs. 10A, B). At the same time answers can be given to the questions as
to how much the embryonic blood-forming organs have to replace worn
out (dead) erythrocytes and what proportion of embryonic erythropoiesis
is devoted to covering the increase in the total erythrocyte number in
the embryonated hen's egg. The overall number of erythrocytes in
circulation starts with one million on the 2nd day, reaching a maximal
value of nearly 8 milliards on the 18th day and falling somewhat thereafter,
probably in connection with the ceasing of the allantoic circulation
(Fig. 10A). The participation of both the primitive and definitive erythrocytes with round nuclei is expressed in Fig. 10A by their survival curves.
From the previous account it is clear that practically all primitive
erythrocytes are destroyed during the incubation period. Because no
distinct cryptogenic turnover of Ε I was found, the total number
produced and destroyed during incubation is equal to the maximal
value on the 6th day—about 110 million. Fig. 10B shows their gradual
destruction from the 7th day of incubation.
The situation is somewhat more complicated in the case of definitive
erythrocytes with round nuclei (E IIj). After the 11th day there is
considerable cryptogenic turnover of about 380 million. When added to
the maximal value (1118-5 million), it can be seen that the total production of this erythrocyte type reaches about 1-5 milliards. The area of the
LEO
LEME2
of embryonal Ε I and Ε IIj erythrocytes was estimated to be below
14,000, less than 10% of the adult values (Lemez and Rychter, 1961).
The high degree of immaturity observed in both lines of embryonic
erythrocytes released into circulation, according to reticulocyte counts
(Lemez, 1953), seems to be the most important factor concerned in
shortening the life span. Considerable shortening of the average life
span of erythrocytes in the rabbit (Neuberger and Niven, 1951) and in
the rat (Berlin and Lötz, 1951), from 67 to 43 days and from 64 to 27
days, respectively, was reported after extensive bleeding compensated
by the release of large numbers of immature erythrocytes (reticulocytes)
into circulation. Further, the high metabolic rate in embryos might
have some effect on life span. Brace (1953) found a considerable
prolongation of the average erythrocyte life span in a hibernating
marmot. Rodnan et al. (1957) demonstrated that the life span of erythrocytes in mammals, birds and reptiles correlates directly with basal heat
production per kilogramme body weight.
H. Balance Sheet of Erythrocyte Production and Destruction
throughout the Incubation Period
Data collected in previous parts of this section make it possible to
strike a balance between red blood cell production and destruction from
the 2nd day of development till the 1st postembryonic day (Table I, and
Figs. 10A, B). At the same time answers can be given to the questions as
to how much the embryonic blood-forming organs have to replace worn
out (dead) erythrocytes and what proportion of embryonic erythropoiesis
is devoted to covering the increase in the total erythrocyte number in
the embryonated hen's egg. The overall number of erythrocytes in
circulation starts with one million on the 2nd day, reaching a maximal
value of nearly 8 milliards on the 18th day and falling somewhat thereafter,
probably in connection with the ceasing of the allantoic circulation
(Fig. 10A). The participation of both the primitive and definitive erythrocytes with round nuclei is expressed in Fig. 10A by their survival curves.
From the previous account it is clear that practically all primitive
erythrocytes are destroyed during the incubation period. Because no
distinct cryptogenic turnover of Ε I was found, the total number
produced and destroyed during incubation is equal to the maximal
value on the 6th day—about 110 million. Fig. 10B shows their gradual
destruction from the 7th day of incubation.
The situation is somewhat more complicated in the case of definitive
erythrocytes with round nuclei (E IIj). After the 11th day there is
considerable cryptogenic turnover of about 380 million. When added to
the maximal value (1118-5 million), it can be seen that the total production of this erythrocyte type reaches about 1-5 milliards. The area of the