220
LEO LEMEZ
(i.e., simultaneous production and destruction of one cell type) in
leucocytes, especially in neutrophils, but unfortunately, unlike the red
cells, no striking morphological label could be found which would enable
the life span to be determined (Section II, G).
D. Other Formed Elements in the Chick Embryo Blood
From the onset of circulation till the 20 to 24 somite stage,
Dantschakoff (1908a) reported the occurrence of cells in the blood
stream which, because of their origin, she called 'Entodermale Wanderzellen'. Swift (1914) identified them as primordial germ cells en route
from the extraembryonically situated germinal crescent to the gonadal
anläge. The cells can, however, also be retained in other, atypical, places
in the chick embryo body (Dantschakoff, 1941).
At about the same period of development large yolk spheres (globules)
may be found in the circulation (Dantschakoff, 1931, 1936, 1941). These
are retained in narrow vessels and resorbed later. Menkes and Litwac
(1953) observed the penetration of yolk spheres into the circulation
after 24 hours of incubation. They regarded them as one possible mode
of early embryonic nourishment.
Sugiyama (1926) observed two types of phagocytic cells in the blood
smears of normal chick embryos. One, present in the earliest stages,
resembled primitive blood cells (haemocytoblasts), and the other
presented the typical appearance of normal clasmatocytes (histiocytes).
The latter were the normal elements of the circulating blood during the
first 8 days of incubation (0-4-1-3% of all blood cells), disappearing
promptly thereafter. Fennell (1947) on the contrary saw only some
vacuolated cells in his smears which might have been the histiocytes
referred to by other authors. This is quite a different finding from
Sugiyama's. The reviewer does not doubt that there are phagocytic cells
(histiocytes) in various places where haematopoiesis takes place
(Dantschakoff, 1908a, b, 1909), but in observing more than 10 million
chick embryo blood cells in smears of circulating blood when counting
leucocytes (Lemez, 1955), no cells were seen which resembled the histiocytes that are so numerous in blood smears from anidian blastoderm
vessels (Section III, B). It seems probable that Sugiyama's blood
samples were taken from blastoderms explanted in hanging-drop
preparations, because he wrote that after 3 days of incubation only the
yolk sac was used. This procedure might have released histiocytes,
occurring in large numbers after cultivation in vitro (Section III, A).
Irradiation of chick embryos at the onset of circulation caused the
appearance of intravascularly localized histiocytes phagocytosing young
erythrocyte forms on the 3rd day of incubation (Dantschakoff, 1936).
The haemocytoblasts with some microvacuoles in their cytoplasm are
LEO LEMEZ
(i.e., simultaneous production and destruction of one cell type) in
leucocytes, especially in neutrophils, but unfortunately, unlike the red
cells, no striking morphological label could be found which would enable
the life span to be determined (Section II, G).
D. Other Formed Elements in the Chick Embryo Blood
From the onset of circulation till the 20 to 24 somite stage,
Dantschakoff (1908a) reported the occurrence of cells in the blood
stream which, because of their origin, she called 'Entodermale Wanderzellen'. Swift (1914) identified them as primordial germ cells en route
from the extraembryonically situated germinal crescent to the gonadal
anläge. The cells can, however, also be retained in other, atypical, places
in the chick embryo body (Dantschakoff, 1941).
At about the same period of development large yolk spheres (globules)
may be found in the circulation (Dantschakoff, 1931, 1936, 1941). These
are retained in narrow vessels and resorbed later. Menkes and Litwac
(1953) observed the penetration of yolk spheres into the circulation
after 24 hours of incubation. They regarded them as one possible mode
of early embryonic nourishment.
Sugiyama (1926) observed two types of phagocytic cells in the blood
smears of normal chick embryos. One, present in the earliest stages,
resembled primitive blood cells (haemocytoblasts), and the other
presented the typical appearance of normal clasmatocytes (histiocytes).
The latter were the normal elements of the circulating blood during the
first 8 days of incubation (0-4-1-3% of all blood cells), disappearing
promptly thereafter. Fennell (1947) on the contrary saw only some
vacuolated cells in his smears which might have been the histiocytes
referred to by other authors. This is quite a different finding from
Sugiyama's. The reviewer does not doubt that there are phagocytic cells
(histiocytes) in various places where haematopoiesis takes place
(Dantschakoff, 1908a, b, 1909), but in observing more than 10 million
chick embryo blood cells in smears of circulating blood when counting
leucocytes (Lemez, 1955), no cells were seen which resembled the histiocytes that are so numerous in blood smears from anidian blastoderm
vessels (Section III, B). It seems probable that Sugiyama's blood
samples were taken from blastoderms explanted in hanging-drop
preparations, because he wrote that after 3 days of incubation only the
yolk sac was used. This procedure might have released histiocytes,
occurring in large numbers after cultivation in vitro (Section III, A).
Irradiation of chick embryos at the onset of circulation caused the
appearance of intravascularly localized histiocytes phagocytosing young
erythrocyte forms on the 3rd day of incubation (Dantschakoff, 1936).
The haemocytoblasts with some microvacuoles in their cytoplasm are