The preceding considerations hold good not alone of increased facilities, but of their curtailment as well. This point is often neglected in respect of capital outlay, which once made cannot be recalled. Rotting of ties we have held to be a constant expense of operation. It goes on steadily, whether traffic conditions be good or bad. But, on the other hand, those ties, if they be under a third or fourth track, would never have been laid had not there been a promise of business sufficient to render the added investment profitable. As Lorenz observes, "the question is not, What expenditures would disappear if a certain proportion of the traffic should be discontinued? but What expenditure would not now be incurred if that traffic had never been called forth?" Viewed in this way, even the necessary replacement of ties under a (temporarily) little used extra track, is an expense determined at some time, even if not always, by the volume of the business. In the long run, therefore, the percentage of total cost which we may assign to an increase in the volume of traffic, is higher than appears from a cross-section of expenses, taken, as was at first had, in a given year. Lorenz has illustrated this steady expansion of all groups of expenditure in relation to expansion of traffic by the following table, in which the actual figures for each year [brought down to date] are replaced by an index number based upon 100 for the year 1895. It would have been highly suggestive to continue all of this data alike to the present time; but, as noted on the table, certain items have been so modified by changes in accounting practice, that this could not be done.