566
E T I E N N E
W O L F F
all (1947), he had shown that a medium deprived of nutrients and
reduced to a simple saline solution could sustain neither differentiation
nor growth. Secondly, he had substituted for the natural medium a
nutritive solution composed of a mixture of amino acids, vitamins and
glucose, following White (1946). This medium allowed good differentiation and a certain amount of growth. If the amino acids, or the vitamins,
or both simultaneously, were removed, morphogenesis was not affected
and growth only slightly inhibited. But, on the contrary, if the glucose
only was omitted, the explants died very rapidly. T o sum up, glucose,
added to the saline solution, provides an energy source sufficient for
morphogenesis of limited duration: it is the minimal requirement of
blastoderms.
In a further study, Spratt (1949) substituted for glucose different
sugars whose energizing properties he studied with regard to differentiation in young embryos removed between the primitive streak stage
and the stage with ten somites. O f sixteen sugars tested only glucose,
mannose, fructose and galactose from the hexose group were utilized;
and only maltose from among the disaccharides. None of the pentoses
gave positive results. From among the products of intermediary metabolism, pyruvate and sodium lactate could also be utilized. But in this
case the differentiation was not as good and lasted for only a short time.
Nevertheless, the various sugars were not all equally efficacious.
The minimum concentrations were as follows: 20 mg % for glucose and
mannose; 50 mg°/o for fructose; 200 m g % for galactose; 400 m g % for
maltose.
Spratt (1950a) also analysed the differential needs ofthe brain and
of the heart during the process of differentiation. He concluded that
if the concentration of glucose or of fructose in the medium is diminished,
differentiation in the nervous system is much more affected than it is in
the heart. Similarly, the heart is much less sensitive than the brain to
different external factors such as anaerobiosis or the lowering of the p H
to 6 or 7.. On the other hand, the main morphogenetic processes,
such as the backward extension of the primitive streak, the formation of
cephalic folds, and the closing of the neural tube, appear to require
fewer energy sources than the processes of differentiation proper, such
as the histogenesis of the brain, optic vesicles, heart, otocysts, and
somites.
Experiments were also done, by cultivation in vitro, on the nutritive
needs ofthe most active region of the embryo, i.e. the region of Hensen's
node. They were done in different media and have shown: (1) that
increasing concentrations of glucose give rise first to survival, then
morphogenetic movements (backward displacement of Hensen's node),
then differentiation, and finally growth; (2) that sugars, given as the
E T I E N N E
W O L F F
all (1947), he had shown that a medium deprived of nutrients and
reduced to a simple saline solution could sustain neither differentiation
nor growth. Secondly, he had substituted for the natural medium a
nutritive solution composed of a mixture of amino acids, vitamins and
glucose, following White (1946). This medium allowed good differentiation and a certain amount of growth. If the amino acids, or the vitamins,
or both simultaneously, were removed, morphogenesis was not affected
and growth only slightly inhibited. But, on the contrary, if the glucose
only was omitted, the explants died very rapidly. T o sum up, glucose,
added to the saline solution, provides an energy source sufficient for
morphogenesis of limited duration: it is the minimal requirement of
blastoderms.
In a further study, Spratt (1949) substituted for glucose different
sugars whose energizing properties he studied with regard to differentiation in young embryos removed between the primitive streak stage
and the stage with ten somites. O f sixteen sugars tested only glucose,
mannose, fructose and galactose from the hexose group were utilized;
and only maltose from among the disaccharides. None of the pentoses
gave positive results. From among the products of intermediary metabolism, pyruvate and sodium lactate could also be utilized. But in this
case the differentiation was not as good and lasted for only a short time.
Nevertheless, the various sugars were not all equally efficacious.
The minimum concentrations were as follows: 20 mg % for glucose and
mannose; 50 mg°/o for fructose; 200 m g % for galactose; 400 m g % for
maltose.
Spratt (1950a) also analysed the differential needs ofthe brain and
of the heart during the process of differentiation. He concluded that
if the concentration of glucose or of fructose in the medium is diminished,
differentiation in the nervous system is much more affected than it is in
the heart. Similarly, the heart is much less sensitive than the brain to
different external factors such as anaerobiosis or the lowering of the p H
to 6 or 7.. On the other hand, the main morphogenetic processes,
such as the backward extension of the primitive streak, the formation of
cephalic folds, and the closing of the neural tube, appear to require
fewer energy sources than the processes of differentiation proper, such
as the histogenesis of the brain, optic vesicles, heart, otocysts, and
somites.
Experiments were also done, by cultivation in vitro, on the nutritive
needs ofthe most active region of the embryo, i.e. the region of Hensen's
node. They were done in different media and have shown: (1) that
increasing concentrations of glucose give rise first to survival, then
morphogenetic movements (backward displacement of Hensen's node),
then differentiation, and finally growth; (2) that sugars, given as the