68 Science and technology The EconomistJanuary 27th 201812 ing”; “for soothing a baby”; “for healing ill-
ness”; “for expressing love for another”;
“for mourning the dead”; and “for telling a
story”. The first four of these were real
functions, as stated by the people from
whom the song in question had been col-
lected. The last two were made up, and
were included as foils.
Dr Mehr and Mr Singh found that vol-
unteers’ perceptions of a song’s function
were generally in good agreement with its
actual function—with one exception.
Dance songs were particularly easy to
identify. They rated 2.18 points higher on
the certainty scale as being used “for danc-
ing” than lullabies did; 1.38 points higher
than love songs; and 1.09 pointshigher
than healing songs. Similarly, lullabies
were rated 1.53 points higher than dance
songs as being “to soothe a baby”, 1.42points higher than healing songs and 1.19
points higher than love songs.
Healing songs proved a bit more trou-
blesome. They scored only 0.47 and 0.31
points higher than dance and love songs
respectively for “to heal illness”, and were
statistically indistinguishable from lulla-
bies. The outlier, though, was love songs.
Listeners could distinguish them from
healing songs, but notfrom lullabies or
dance songs.
Why love songs were hard to identify is
unclear. Because such songs involve show-
ing off to the objectof one’s affections, they
may require more creativity, and thus gen-
erate more variety than lullabiesor dance
songs. Perhaps the fact that both dancing
and cooing are involved in romance con-
fused listeners. This genre aside, however,
Andersen was clearly onto something. 7W
HEN Constantin Coussios, a bio-
medical engineer at Oxford Universi-
ty, arrived one day in 2013 at the transplant
centre of King’s College Hospital, in Lon-
don, with a liver for their use, he triggered a
brief flurry of panic. Two other livers had
arrived at the same time. The hospital had
only one operating theatre in which liver
transplants could be carried out—and be-
cause livers intended for transplantcan be
kept in cold storage for no longer than 12
hours, the situation looked serious.
What saved the day, and possibly a pa-
tient’s life, was that Dr Coussios was bring-
ing not a cold liver, stored on ice, but a
warm one. Instead of having had its me-
tabolism slowed, it was fully functional.
This was because it was connected to a
supply of blood and nutrients inside a spe-
cial box known as a metra (a Greek word
meaning “womb”), invented by Dr Cous-
sios and his colleague Peter Friend. The me-
tra even had a graphical interface to show,
moment by moment, how well its cargo
was faring. DrCoussios told the surgeon to
transplantthe cold-stored livers first. The
one he had brought would keep.
That was in the early days of metras.
Now, the devices are starting to spread. So
far 25 have been deployed around the
world and others are about to be. There are
also plans, by Dr Coussios and others, to
extend the idea behind the metra to the
preservation of other vital organs. If that
works, it would change the transplant
business by improving both the supply
and the health of such organs.A metra is designed to keep the organ it
is nurturing supplied with the correct
amount of blood—an amount which va-
ries from one instant to the next. It detects
the organ’s demand for blood by monitor-
ing pressure in the arteries and veins going
into and out of the liver. It then adjusts the
power of its pump in response.
The blood in question has been tin-
kered with to make it more effective. It has
had its white cells and platelets removed to
avoid inflammation, clotting and the trans-
fer of disease. For the further prevention of
clotting, it has had anticoagulants added.
And it hasbeen boosted with special
chemicals that the liver needs in order toproduce bile; with insulin to regulate the
organ’s metabolism; and with nutrition in
the form of glucose and amino acids.
Once a liver ishooked up inside a me-
tra, its health can be tracked by monitoring
things like blood flow, bile production and
acidity levels. All these data permit a trans-
plant team to see how the organ is faring.
Moreover, a metra not only keeps a liver
healthy but can, in some circumstances, ac-
tually improve its health. Putting a liver
that has been cooled for storage into a me-
tra can reverse damage it has sustained
when cold by providing an environment
in which its natural propensity to rejuve-
nate can come to the fore. More remark-
ably, metras may even be able to recondi-
tion livers that are sickly because they
contain too much fat, and are thus untrans-
plantable. Once a liver has been removed
from the body that was making it fat, it will
recover surprisingly quickly. A mere two
days in a metra “liver spa” is enough to
have a palpable positive effect on the
health of such an organ.
At the moment, this lastbenefit is of
only theoretical value, because regulations
mean livers for transplant can be stored in
a metra for a maximum of 24 hours. That,
though, is twice the maximum a liver
ought to be kept chilled for transplant, and
almost three times the nine-hour limit gen-
erally preferred—hence Dr Coussios’s in-
souciance at the hospital backin 2013. Re-
search on metras suggests that the 24-hour
limit could safely be raised to three days,
and possibly longer than that.
Twenty-four hours is, though, still long
enough to conduct tests on the quality of
livers that might otherwise be rejected. The
existing assessment of a liver for transplant
is necessarilysubjective, because there is
no sure way to tell if a cooled organ will
work normally when it is warmed up and
reconnected. Many surgeons therefore err
on the side of caution, knowing that if they
put a defective liver into a patient, it will
probably kill him.
All this means that using metras should
increase the availability of livers for trans-
plant. Dr Coussios reckons thatreducing
the rate of rejection by surgeons could, by
itself, double the number which can be
used in Britain. Metras could also make it
easier to perform the tricky operation of
splitting livers in two, which is sometimes
done to create a child-sized organ while
still leaving enough over to transplant into
an adult. The use of a metra is likely to per-
mit these divisions to be carried out more
slowly and carefully.
The metra is being commercialised by
OrganOx, a firm based in Oxford. Dr Cous-
sios estimates that the world’s hospitals
have need for about 300 of the machines,
but the firm says it will have reliable repeat
business from furnishing the metras it has
sold with the disposable plasticconnec-
tors that hook machine and organ up to-MedicineExternal organs
Livers for transplant can now be kept alive at body temperatureNow for a bit of metra-analysisРЕЛИЗ
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