A fourth group of expenditures remains, denominated General Expenses. This includes all salaries of principal administrative officers from the president or receiver down to the real estate and tax agents, together with all their allowances for expenses, special cars or trains and the like. All clerical salaries in the general offices naturally belong here, as well as most of the legal expenses, outlay for pensions, relief departments and the like. A distinct improvement in the matter of principle has been made in the revised classification of operating expenses under the new law of 1906, by the segregation of a fifth group, denominated Traffic Expenses.[30] These cover all the work of soliciting business, making rates and accounting for freight and passenger traffic. Such outlays were formerly grouped in the main under conducting transportation, but, as is quite evident, they are distinct in their nature from the expenses incidental to the actual handling of trains. Administrative railroad organization has long recognized the peculiar and important nature of this work by constituting it a separate department, usually headed by one of the vice-presidents of the road. The main items under this special head are salaries and expenses of a large staff of officers and clerks, such as general passenger and freight managers, agents and travelling solicitors; rents and care of offices at home or abroad; advertising, membership in traffic associations, immigration and industrial bureaus, expenses for experimental farms, field demonstrators, donations to expositions, fairs and stock shows--everything, in brief, which tends to create or keep business, to be afterward actually handled by the transportation departments. In future the detailed official statistics will segregate these expenses; but at the present writing and in statistics down to 1906 they must be bulked in with conducting transportation. An important modification in accounting under the new law of 1906 has also been made in respect to depreciation charges. Heretofore the practice of companies varied widely, as will hereafter be shown. Under the new rulings a definite and uniform system of charging off for depreciation has to be provided, the details of which, however, need not concern us at this time.[31] The following table based upon the returns for 1905 shows the relative importance of the principal items under railroad expenditures grouped under the proper headings: