'At the Book Fair of Leipsic, booksellers from all over Germany arrive, each with four or five publications of his own in some 40 or 50 dozen copies; these are exchanged for others and every seller takes home 200 dozen books, just as he has brought 200 dozen, with the sole difference, that he brought four different works and takes home 200. This is the demand and the production which, according to M. Ricardo's disciple, are correlative and convertible; one buys the other, one pays for the other, one is the consequence of the other. But as far as we are concerned, for the bookseller and for the general public, demand and consumption have not even begun. For all that it has changed hands at Leipsic, a bad book will still be just as unsold (a bad mistake of Sismondi's, this!), it will still clutter up the merchants' shops, either because nobody wants it, or because everyone has a copy already. The books exchanged at Leipsic will only sell if the booksellers can find individuals who not only want them but are also prepared to make sacrifices in order to withdraw them from circulation. They alone constitute an effective demand.'[182] Although this example is rather crude, it shows clearly that Sismondi was not side-tracked by his opponent's trick, that he knows after all what he is talking about. MacCulloch then attempts to turn the examination from abstract commodity exchange to concrete social conditions: 'Supposing, for the sake of illustration, that a cultivator advanced food and clothing for 100 labourers, who raised for him _food_ for 200; while a master-manufacturer also advanced food and clothing for 100, who fabricated for him _clothing_ for 200. Then the farmer, besides replacing the food of his own labourers, would have food for 100 to dispose of; while the manufacturer, after replacing the clothing of his own labourers, would have clothing for 100 to bring to market. In this case, the two articles would be exchanged against each other, the supply of food constituting the demand for the clothing, and that of the clothing the demand for the food.'[183]