670
H O N O R
B .
F E L L
A N D
L .
M .
R I N A L D I N I
FIG. 11. Electron-micrograph of a superficial cell in a similar explant to that shown in Fig. 10,
grown for 7 days in medium containing 1 0 i.u./ml. of added vitamin A. Note microvilli,
secretory vacuoles, swollen mitochondria and absence of keratinization. X 25,000. (Fitton
Jackson and Fell.)
epithelium beneath the secretory layer which is then shed. Keratinization is inhibited if vitamin A is added to the medium.
These experiments were made in natural media. Recently, Lasnitzki
(1961), using mouse vagina, has shown that the same results can be
obtained in chemically defined medium (modified Connaught 858).
Since vitamin A breaks down rapidly in defined medium, the explants
were pre treated by a brief incubation in medium containing the vitamin
in high concentration, and then transferred to medium without the
vitamin. This pretreatment suppressed keratin-formation and preserved the original epithelium. It also stimulated the proliferation of the
new epithelium and evoked the formation of keratohyalin.
3. Oesophagus
Aydelotte (1963b) has shown that when explants of the oesophagus
from 13-day chick embryos are grown in the presence of excess of
H O N O R
B .
F E L L
A N D
L .
M .
R I N A L D I N I
FIG. 11. Electron-micrograph of a superficial cell in a similar explant to that shown in Fig. 10,
grown for 7 days in medium containing 1 0 i.u./ml. of added vitamin A. Note microvilli,
secretory vacuoles, swollen mitochondria and absence of keratinization. X 25,000. (Fitton
Jackson and Fell.)
epithelium beneath the secretory layer which is then shed. Keratinization is inhibited if vitamin A is added to the medium.
These experiments were made in natural media. Recently, Lasnitzki
(1961), using mouse vagina, has shown that the same results can be
obtained in chemically defined medium (modified Connaught 858).
Since vitamin A breaks down rapidly in defined medium, the explants
were pre treated by a brief incubation in medium containing the vitamin
in high concentration, and then transferred to medium without the
vitamin. This pretreatment suppressed keratin-formation and preserved the original epithelium. It also stimulated the proliferation of the
new epithelium and evoked the formation of keratohyalin.
3. Oesophagus
Aydelotte (1963b) has shown that when explants of the oesophagus
from 13-day chick embryos are grown in the presence of excess of