1010
TAR +
ey
J
l
IT
\,
-
fe
=z
ia
-
& SOF
a
:
o
=8
aor
Ur &
*,
= 25 }—
-4
\\
\
i
Leuer"~
—
t+—
ma
“On
—
\t
\
woe 3
ye
oO
l
|
{
0
600
{200
X-RAY DOSE, R
h
|
1600
Fig. 12—Incorporation of thymidine (TdR), uridine (Ur), and leucine (Lew at
different doses of irradiation.
Between 800 and 1200 R, which are doses acting upon differentia-
tion, only the DNA synthesis is notably affected (Fig. 12).
scusson
BEST AVAILABLE COPY
The fact that irradiation of the inductors does not affect their inductive capacity suggests either that the active factors have already
been synthesized and stored in the cells or that synthesis goes on
despite irradiation.
If we assume that the inductive substance is a protein, this could
also mean that the phase of protein synthesisis not very radiosensitive.
However, irradiation of the responding cells prevents their differentia-
tion, which, in normal tissues, is always accompanied by a definite in-
crease of the DNA synthesis, This may suggest that the primary target
of the irradiation {s the DNA synthesis ofthe differentiating tissues.
Far reaching conclusions should not be drawn from these fragmentary results, We know too little about genetic information in the
cells of Metazoans to make further hypotheses on this subject.
REFERENCES
1. ¥. C. Kong, M. Reyss-Brion, and J. M. Kirrmann, Etude du meétabolisme
macromoléculaire depeau embryonnaire de Ponlet, en culture organotyplopie.
Effet des radiations fonisantes, Arch. Sc. Physiol. (in press).
2. Etfenne Wolff and K. Haffen, A Method of Culturing Embryonic Organs in
Vitro, Tex. Rep. Biol. Med., 10: 463-472 (1952).