[Footnote 2:  P. 255.]

[Footnote 3:  Reg.  Fus.  Tract., XXXVII. i.]

[Footnote 4:  Quoted in Janssen, op. cit., vol. ii. p. 9.]

Finally, it must be clearly understood that the attempt of some modern writers to base the mediaeval justification of commerce on an analysis of all commercial gains as the payment for labour rests on a profound misunderstanding.  As we have already pointed out, Aquinas distinctly rules out of consideration in his treatment of commerce the case where the goods have been improved in value by the exertions of the merchant.  When the element of labour entered into the transaction the matter was clearly beyond doubt, and the lengthy discussion devoted to the question of commerce by Aquinas and his followers shows that in justifying commercial gains they were justifying a gain resting not on the remuneration for the labour, but on an independent title.

Sec. 8. Cambium.

There was one department of commerce, namely, cambium, or money-changing, which, while it did not give any difficulty in theory, involved certain difficulties in practice, owing to the fact that it was liable to be used to disguise usurious transactions.  Although cambium was, strictly speaking, a special branch of commerce, it was nevertheless usually treated in the works on usury, the reason being that many apparent contracts of cambium were in fact veiled loans, and that it was therefore a matter of importance in discussing usury to explain the tests by which genuine and usurious exchanges could be distinguished.  Endemann treats this subject very fully and ably;[1] but for the purpose of the present essay it is not necessary to do more than to state the main conclusions at which he arrives.

[Footnote 1:  Studien, vol. i. p. 75.]

Although the practice of exchange grew up slowly and gradually during the later Middle Ages, and, consequently, the amount of space devoted to the discussion of the theory of exchange became larger as time went on, nevertheless there is no serious difference of opinion between the writers of the thirteenth century, who treat the subject in a fragmentary way, and those of the fifteenth, who deal with it exhaustively and systematically.  Aquinas does not mention cambium in the Summa, but he recognises the necessity for some system of exchange in the De Eegimine Principum.[1] All the later writers who mention cambium are agreed in regarding it as a species of commerce to which the ordinary rules regulating all commerce apply.  Francis de Mayronis says that the art of cambium is as natural as any other kind of commerce, because of the diversity of the currencies in different kingdoms, and approves of the campsor receiving some remuneration for his labour and trouble.[2] Nicholas de Ausmo, in his commentary on the Summa Pisana, written in the beginning of the fifteenth century, says that the campsor may