98
'
_
FREEZE—DRYING
—
Of great theoretical interest was Meryman’s experiment of frèeze—drying his _frozen
red cell sand.
After drying there was complete lysis of the red cells if they were suspended
inçnormal saline,thus demonstrating that there was further injury to the red cell membrane
on drying. However, if the, dried cells wererehydrated in 40 % P. V. P. there was a fair
recovery of intact cells. This was probably due to an osmotic trick, for on
the
P. V.P. and substituting normal Saline, many of the cells were lysed.
The experimentwould suggest that for successful drying not only must we, freeze with
‘
a
additive, but that further protective substances must be looked for which
will protect the cell membrane from injury during drying.
_
,
Mazur (1960) has studied in great detail the lethal affects of freezing on theyeast
Saccharomyces cerevisiae and (1965) the e"ect Of freezing on the permeability, of
!
the cell membrane of
yeast.
He _showed that this organism was highly susceptible
'
‘
to rapid freezing and slow .thawing, though it was relatively insensitive to slow freezing
and rapid thawing.
wasablè to demonstrate that death occurred if intracellular crystalisation occurred, though if=the intracellular contents remained supercooled no death
a temperature which, would have been fatal if ice crystals had formed. He
,
showed that
of
intracellularsupercooled uid wasrelated to the radius of the
i
ice—crystals in the extracellular uid, and Figure 1. shows his diagramatic representation
of the mechanisms of the .seeding through pores in the cell membrane.
Mazur (1965)
also demonstratedthä…t after intracellular ice-crystal formation on thawing, the intracellular
uid escaped from the cell, thus proving that the cell wall had been injured on freezing,
so that there was an increase in permeability. Anexplatnation must be found, however,
for the fact that this yeast survives slow freezing and fast thawing very well, even if the
freezing temperature is taken well*below that at which supercooling, might be expected.
One possible explanation would be if the
contained a protective substance. This
might well be below
concentration to prevent salt concentration on freezing,
but if freezing were slow, the slow growth of extracdlular ice crystals might encourage the
passage of water from the intra to…the extracellular uid so concentrating the protective
substance.
Testing this exPerimentally, Davies found that the intracellular material of
this yeast was able to suppre‘ss the eutectic of sodium chloride.
…
_
,
.
,
It is not possible frôm the available evidence to say
the electrQlyte concentration
or the intracellular crystallisation theory for the destructivee‘ect of freezing and thawing
is correct.
Certainly1fcrystallisation occurs there is an.immediate concentrati0n of elec—
trolytes unless a protective substance
present which reduces the amouhtof water Wh10h
undergoes
change and then…proceeds to
a glass preventing further.
consentr@tii}gthe
,
:
«Ænf f4nl
'
bY.iÏce,
fmicfOètaphs were ïàdc
which had been
ËËÊÊZÏQ,gâ@d
& typisa1
of
see- …It
‘
1148
tom
'
'
_
The
occurred
…
-
fatherthancrystalpuncture
…
l
Fortunaœlymanybaoterlaandv1ruses areh1ghlyresxstmttofreezethawanddrymg
'
'
_
FREEZE—DRYING
—
Of great theoretical interest was Meryman’s experiment of frèeze—drying his _frozen
red cell sand.
After drying there was complete lysis of the red cells if they were suspended
inçnormal saline,thus demonstrating that there was further injury to the red cell membrane
on drying. However, if the, dried cells wererehydrated in 40 % P. V. P. there was a fair
recovery of intact cells. This was probably due to an osmotic trick, for on
the
P. V.P. and substituting normal Saline, many of the cells were lysed.
The experimentwould suggest that for successful drying not only must we, freeze with
‘
a
additive, but that further protective substances must be looked for which
will protect the cell membrane from injury during drying.
_
,
Mazur (1960) has studied in great detail the lethal affects of freezing on theyeast
Saccharomyces cerevisiae and (1965) the e"ect Of freezing on the permeability, of
!
the cell membrane of
yeast.
He _showed that this organism was highly susceptible
'
‘
to rapid freezing and slow .thawing, though it was relatively insensitive to slow freezing
and rapid thawing.
wasablè to demonstrate that death occurred if intracellular crystalisation occurred, though if=the intracellular contents remained supercooled no death
a temperature which, would have been fatal if ice crystals had formed. He
,
showed that
of
intracellularsupercooled uid wasrelated to the radius of the
i
ice—crystals in the extracellular uid, and Figure 1. shows his diagramatic representation
of the mechanisms of the .seeding through pores in the cell membrane.
Mazur (1965)
also demonstratedthä…t after intracellular ice-crystal formation on thawing, the intracellular
uid escaped from the cell, thus proving that the cell wall had been injured on freezing,
so that there was an increase in permeability. Anexplatnation must be found, however,
for the fact that this yeast survives slow freezing and fast thawing very well, even if the
freezing temperature is taken well*below that at which supercooling, might be expected.
One possible explanation would be if the
contained a protective substance. This
might well be below
concentration to prevent salt concentration on freezing,
but if freezing were slow, the slow growth of extracdlular ice crystals might encourage the
passage of water from the intra to…the extracellular uid so concentrating the protective
substance.
Testing this exPerimentally, Davies found that the intracellular material of
this yeast was able to suppre‘ss the eutectic of sodium chloride.
…
_
,
.
,
It is not possible frôm the available evidence to say
the electrQlyte concentration
or the intracellular crystallisation theory for the destructivee‘ect of freezing and thawing
is correct.
Certainly1fcrystallisation occurs there is an.immediate concentrati0n of elec—
trolytes unless a protective substance
present which reduces the amouhtof water Wh10h
undergoes
change and then…proceeds to
a glass preventing further.
consentr@tii}gthe
,
:
«Ænf f4nl
'
bY.iÏce,
fmicfOètaphs were ïàdc
which had been
ËËÊÊZÏQ,gâ@d
& typisa1
of
see- …It
‘
1148
tom
'
'
_
The
occurred
…
-
fatherthancrystalpuncture
…
l
Fortunaœlymanybaoterlaandv1ruses areh1ghlyresxstmttofreezethawanddrymg
'