2 . M E T H O D S
83
body size (Weymouth, Field and Kleiber, 1942; Davies, 1961). The
relationship is 00 2 =kW~
p
, where k and/? are constants. It appears therefore that rats and mice, being amongst the smallest mammals, are unsuitable for organ culture. In the cow, by contrast, tissue oxygenconsumption is only one third as great and, by calculation, this should
increase the limiting culture diameter from 2 mm to 3-5 mm, which
means a fivefold increase in volume. Trowell (1961a) cultured pieces of
various organs from the cow and found that this prediction was
roughly true; cultures about 4 mm in diameter weighing 20 mg could be
maintained (in oxygen) without central necrosis. It is probable that
human material which is easier to obtain under aseptic conditions
(from the operating theatre) would offer similar advantages.
2. Survival Time
Embryonic organs generally survive in culture for some months,
during which time they undergo normal organotypic growth. Ultimately
they become too big and for this reason undergo central necrosis.
Mature organs on the other hand survive for a much shorter time,
generally about a week, though some, such as prostate, thyroid and
pituitary, may last a little longer (Fig. 9). The reason for this difference
is not known. Perhaps embryonic organs retain more independence and
autonomy; perhaps incompletely differentiated cells are more robust
and more adaptable to abnormal conditions; perhaps it is because
embryonic cells are less dependent on respiration, which is known to
fail progressively in vitro, a point which will be elaborated later.
The question of temperature has been raised and can be dealt with
first. Martinovitch (1951) claimed that mammalian organs survived
longer if incubated at subnormal temperature (32-34°C), but this
does not seem to have been a general experience. If it could be shown
that the temperature coefficient of anabolic processes was less than that
of catabolic processes it could be argued that subnormal temperature
should be beneficial. But such evidence as there is indicates that energyyielding processes such as respiration have a higher temperature coefficient than autolytic processes. It is true that lowering the temperature reduces the rate of metabolism and therefore the risk of central
necrosis but, on the other hand, certain essential services such as the
sodium and water pumps must be maintained, otherwise the whole
state of the cell is upset, and it seems doubtful if cells geared to work
at 37°C would work as efficiently at some other temperature.
Trowell (1961a) tried to find out why the survival time of mature
organs is so limited, but without success. He tried a great many culture
media, ranging from simple to complex, both natural and artificial,
and concluded that nutritional deficiency was not responsible. The fact,
83
body size (Weymouth, Field and Kleiber, 1942; Davies, 1961). The
relationship is 00 2 =kW~
p
, where k and/? are constants. It appears therefore that rats and mice, being amongst the smallest mammals, are unsuitable for organ culture. In the cow, by contrast, tissue oxygenconsumption is only one third as great and, by calculation, this should
increase the limiting culture diameter from 2 mm to 3-5 mm, which
means a fivefold increase in volume. Trowell (1961a) cultured pieces of
various organs from the cow and found that this prediction was
roughly true; cultures about 4 mm in diameter weighing 20 mg could be
maintained (in oxygen) without central necrosis. It is probable that
human material which is easier to obtain under aseptic conditions
(from the operating theatre) would offer similar advantages.
2. Survival Time
Embryonic organs generally survive in culture for some months,
during which time they undergo normal organotypic growth. Ultimately
they become too big and for this reason undergo central necrosis.
Mature organs on the other hand survive for a much shorter time,
generally about a week, though some, such as prostate, thyroid and
pituitary, may last a little longer (Fig. 9). The reason for this difference
is not known. Perhaps embryonic organs retain more independence and
autonomy; perhaps incompletely differentiated cells are more robust
and more adaptable to abnormal conditions; perhaps it is because
embryonic cells are less dependent on respiration, which is known to
fail progressively in vitro, a point which will be elaborated later.
The question of temperature has been raised and can be dealt with
first. Martinovitch (1951) claimed that mammalian organs survived
longer if incubated at subnormal temperature (32-34°C), but this
does not seem to have been a general experience. If it could be shown
that the temperature coefficient of anabolic processes was less than that
of catabolic processes it could be argued that subnormal temperature
should be beneficial. But such evidence as there is indicates that energyyielding processes such as respiration have a higher temperature coefficient than autolytic processes. It is true that lowering the temperature reduces the rate of metabolism and therefore the risk of central
necrosis but, on the other hand, certain essential services such as the
sodium and water pumps must be maintained, otherwise the whole
state of the cell is upset, and it seems doubtful if cells geared to work
at 37°C would work as efficiently at some other temperature.
Trowell (1961a) tried to find out why the survival time of mature
organs is so limited, but without success. He tried a great many culture
media, ranging from simple to complex, both natural and artificial,
and concluded that nutritional deficiency was not responsible. The fact,