o be much disputed
whether anything else, such as a slave, a piece of land, or a robe,
could be treated as a price. Sabinus and Cassius held the affirmative,
explaining thus the common theory that exchange is a species, and the
oldest species, of purchase and sale; and in their support they quoted
the lines of Homer, who says in a certain passage that the army of the
Greeks procured themselves wine by giving other things in exchange,
the actual words being as follow: 'then the longhaired Greeks bought
themselves wine, some with bronze, some with shining iron, some
with hides, some with live oxen, some with slaves.' The other school
maintained the negative, and distinguished between exchange on the one
hand, and purchase and sale on the other: for if an exchange were the
same thing as a sale, it would be impossible to determine which is the
thing sold, and which is the price, and both things cannot be regarded
in each of these characters. The opinion, however, of Proculus, who
affirmed that exchange was a species of contract apart by itself, and
distinct from sale, has deservedly prevailed, as it is confirmed by
other lines from Homer, and by still more cogent reasons, and this has
been admitted by preceding Emperors, and is fully stated in our Digest.

3 As soon as the contract of sale is concluded--that is, as we have
said, as soon as the price is agreed upon, if the contract is not in
writing--the thing sold is immediately at the risk of the purchaser,
even though it has not yet been delivered to him. Accordingly, if a
slave dies, or is injured in any part of his body, or if a house is
either totally or partially burnt down, or if a piece of land is wholly
or partially swept away by a river flood, or is reduced in acreage by
an inundation, or made of less value by a storm blowing down some of
its trees, the loss falls on the purchaser, who must pay the price even
though he has not got what he purchased. The vendor is not responsible
and does not suffer for anything not due to any design or fault of his
own. If, however, after the purchase of a piece of land, it receives an
increase by alluvion, it is the purchaser who profits thereby: for the
profit ought to belong to him who also bears the risk. And if a slave
who has been sold runs away, or is stolen, without any design or fault
of the vendor, one should look to see whether the latter expressly
undertook to keep him safely until delivery was made; for, if he did
thi