In truth, this discovery of a convenient means of effecting exchanges makes no alteration in the nature either of men or of things. We have still in every case the ‹want› which determines the ‹effort›, and the ‹satisfaction› which rewards it. The Exchange is complete only when the man who has made an ‹effort› in favour of another has obtained from him an equivalent service, that is to say, ‹satisfaction›. To effect this, he ‹sells› his service for the intermediate commodity, and then with that intermediate commodity he ‹purchases› equivalent services, when the two factors bring back the transaction to simple ‹barter›. Take the case of a physician, for instance. For many years he has devoted his time and his faculties to the study of diseases and their remedies. He has visited patients, he has prescribed for them, in a word, he has rendered ‹services›. Instead of receiving compensation from his patients in ‹direct services›, which would have constituted simple barter, he receives from them an intermediate commodity, the precious metals, wherewith he purchases the satisfactions which were the ultimate object he had in view. His patients have not furnished him with bread, wine, or other goods, but they have furnished him with the value of these. They could not have given him money unless they had themselves rendered ‹services›. As far as they are concerned, therefore, there is a balance of ‹services›, and there is also a balance as regards the physician; and could we in thought follow this circulation of services out and out, we should see that Exchange carried on by the intervention of money resolves itself into a multitude of acts of simple barter. In the case of simple barter, ‹value› is the appreciation of two services exchanged and directly compared with each other. In the case of ‹Compound Exchange› the two services measure each other’s value, not directly, but by comparison with this mean term, this intermediate commodity, which is called Money. We shall see by-and-by what difficulties, what errors, have sprung from this complication. At present it is sufficient to remark that [p111] the intervention of this intermediate commodity makes no change whatever in the notion of ‹value›.