674
H O N O R
B .
F E L L
A N D
L .
M .
R I N A L D I N I
When this research began in 1952 (Fell and Mellanby, 1952), it was
well known that, in animals, excess of vitamin A caused resorption of
cartilage and bone, but it was not known whether this effect was due
to a direct action of the vitamin on the skeleton or whether it was
mediated through some systemic reaction. The original experiments
on the cultivation of bone rudiments in medium containing excess of this
G
+ A
L
FIG. 16. Serial photographs of a pair of living humeri from a 6-day chick embryo, grown
8 days in normal medium (C) and in the presence of 10 i.u./ml of vitamin A ( + A ) . The
cartilaginous rudiments were photographed at explantation and thereafter at two-day
intervals.