688
H O N O R
B . F E L L
A N D L . M . R I N A L D I N I
those found in tissues, but they are never attained in the blood because
of the renal threshold. In the whole animal, very high doses administered
orally or intravenously are promptly excreted, and therefore have no
toxic effect on the cells. This situation cannot be compared with that
obtained in a closed system, like that in cultures, where there are no
excretory mechanisms. It may be added here that Shapiro (1948)
found inhibition of mitosis in sea urchin eggs with doses of the same
order.
When ascorbic acid was incorporated in a growth-promoting medium
containing embryo extract, the inhibitory effect on the initial expansion
of the cells was much less marked, although their subsequent growth—
i.e. the net increase in cell number after 4 days—was sub-normal. If
the compound was added 48 h after inoculation, when the cells had
spread and the population had already grown, the effect was insignificant. It seems, therefore, that embryo extract is able to neutralize to a
large extent the toxic effect of excess ascorbic acid. This cannot be
attributed to destruction ofthe vitamin, since we have seen that embryo
juice itself contains a high concentration of ASA and protects it from
oxidation.
A forgotten observation of Gaillard (1942) reveals a dramatic effect
of ASA on differentiation. Four cultures of Ehrlich's carcinoma, after
680 passages, could be induced to differentiate into cartilage (3 cultures)
and bone (1 culture) by adding vitamin C to the medium. The specificity of this effect certainly merits further exploration. It may well be
that ASA, though not required by most tissue cells for maintenance or
growth, is essential for some specialized functions such as the building
of normal intercellular materials.
The most obvious effects of vitamin C deprivation are exerted on
the mesenchymal tissues (see review by Reid, 1954) and it is generally
agreed that ascorbic acid is necessary for the normal formation of
collagen and possibly other extracellular components, but its mode of
action has been long debated and is still not quite clear (see discussion
by Gould, 1961; Robertson, 1961). After continued research on the
subject, Robertson (1961) summarizes the evidence saying that "small
amounts of collagen may apparently be synthesized in the absence of
demonstrable ascorbic acid, but the rapid synthesis of large amounts
of collagen requires ascorbic acid" and that "maintenance of preformed
collagen does not generally require ascorbic acid, but a deficiency of
the vitamin may result in loss of collagen from tissues that still contain
a large number of fibrocytes".
The elegant and simple experiments of Gould (1958), who induced
collagen synthesis by local injection of ASA in only one of a pair of
plastic sponge granulomas in scorbutic guinea-pigs, were confirmed
H O N O R
B . F E L L
A N D L . M . R I N A L D I N I
those found in tissues, but they are never attained in the blood because
of the renal threshold. In the whole animal, very high doses administered
orally or intravenously are promptly excreted, and therefore have no
toxic effect on the cells. This situation cannot be compared with that
obtained in a closed system, like that in cultures, where there are no
excretory mechanisms. It may be added here that Shapiro (1948)
found inhibition of mitosis in sea urchin eggs with doses of the same
order.
When ascorbic acid was incorporated in a growth-promoting medium
containing embryo extract, the inhibitory effect on the initial expansion
of the cells was much less marked, although their subsequent growth—
i.e. the net increase in cell number after 4 days—was sub-normal. If
the compound was added 48 h after inoculation, when the cells had
spread and the population had already grown, the effect was insignificant. It seems, therefore, that embryo extract is able to neutralize to a
large extent the toxic effect of excess ascorbic acid. This cannot be
attributed to destruction ofthe vitamin, since we have seen that embryo
juice itself contains a high concentration of ASA and protects it from
oxidation.
A forgotten observation of Gaillard (1942) reveals a dramatic effect
of ASA on differentiation. Four cultures of Ehrlich's carcinoma, after
680 passages, could be induced to differentiate into cartilage (3 cultures)
and bone (1 culture) by adding vitamin C to the medium. The specificity of this effect certainly merits further exploration. It may well be
that ASA, though not required by most tissue cells for maintenance or
growth, is essential for some specialized functions such as the building
of normal intercellular materials.
The most obvious effects of vitamin C deprivation are exerted on
the mesenchymal tissues (see review by Reid, 1954) and it is generally
agreed that ascorbic acid is necessary for the normal formation of
collagen and possibly other extracellular components, but its mode of
action has been long debated and is still not quite clear (see discussion
by Gould, 1961; Robertson, 1961). After continued research on the
subject, Robertson (1961) summarizes the evidence saying that "small
amounts of collagen may apparently be synthesized in the absence of
demonstrable ascorbic acid, but the rapid synthesis of large amounts
of collagen requires ascorbic acid" and that "maintenance of preformed
collagen does not generally require ascorbic acid, but a deficiency of
the vitamin may result in loss of collagen from tissues that still contain
a large number of fibrocytes".
The elegant and simple experiments of Gould (1958), who induced
collagen synthesis by local injection of ASA in only one of a pair of
plastic sponge granulomas in scorbutic guinea-pigs, were confirmed