ΐ . P R O B L E M O F T H E O R G A N I Z E R
37
treated explants developing only epidermal cells (Table V; Fig. 14).
The very infrequent archencephalic or non-regional neural effects
observed can be well caused by slight toxicity or mechanical injury
during the manipulation. In this connection it should be pointed out
that a large number of experiments conducted for the purpose of finding
out the morphogenetic activity of RNA have led to results similar to
ours. Kuusi (1953) tested a commercial sample of RNA and a sample of
rabbit RNA in insertion experiments and on ectoderm explants cultured
in vitro. Although in some cases weak archencephalic effects were found,
F I G . 1 4 . Isolated ectoderm cultured in a solution of t h y m u s R N A with serum
albumin. A n irregular cluster of epidermal cells are formed, which are not distinguishable
from an explant of the control series, χ 90.
no clear evidence for specific inductive effects of RNA was found.
Yamada, K. Takata, and Osawa (1954) prepared RNA samples of guineapig kidney according to the method of Grinnan and Mosher and other
methods and tested its effect on the ectoderm of Triturus embryos by
using the sandwich technique. In most series weak archencephalic
effects were found. No spino-caudal or deuterencephalic effects which
characterize the original tissue were obtained. Tiedemann and
Tiedemann (1956b) prepared RNA from the chick embryo and ox liver
by a technique which involved phenol extraction, tested the sample in
insertion experiments on Triturus gastrulae, and noticed only weak
reactions of indifferent neural or archencephalic types. Engländer and
37
treated explants developing only epidermal cells (Table V; Fig. 14).
The very infrequent archencephalic or non-regional neural effects
observed can be well caused by slight toxicity or mechanical injury
during the manipulation. In this connection it should be pointed out
that a large number of experiments conducted for the purpose of finding
out the morphogenetic activity of RNA have led to results similar to
ours. Kuusi (1953) tested a commercial sample of RNA and a sample of
rabbit RNA in insertion experiments and on ectoderm explants cultured
in vitro. Although in some cases weak archencephalic effects were found,
F I G . 1 4 . Isolated ectoderm cultured in a solution of t h y m u s R N A with serum
albumin. A n irregular cluster of epidermal cells are formed, which are not distinguishable
from an explant of the control series, χ 90.
no clear evidence for specific inductive effects of RNA was found.
Yamada, K. Takata, and Osawa (1954) prepared RNA samples of guineapig kidney according to the method of Grinnan and Mosher and other
methods and tested its effect on the ectoderm of Triturus embryos by
using the sandwich technique. In most series weak archencephalic
effects were found. No spino-caudal or deuterencephalic effects which
characterize the original tissue were obtained. Tiedemann and
Tiedemann (1956b) prepared RNA from the chick embryo and ox liver
by a technique which involved phenol extraction, tested the sample in
insertion experiments on Triturus gastrulae, and noticed only weak
reactions of indifferent neural or archencephalic types. Engländer and