Deductions from the full tariff for the use of special equipment owned by shippers, has been one of the commonest means of building up great monopolies.[171] The allowances to the Standard Oil Company for the use of its tank cars, before the construction of pipe lines, and especially prior to 1888, were a source of great unrest.[172] But the construction of pipe lines has not lessened their importance. It is on record that the use of private cars in other lines of business has led to grave abuses. When stock cars and beef refrigerator cars, owned by private shippers, first began to be used about 1883-1884, they were much sought after by the railroads as traffic. They moved regularly, not by seasons; the volume of business was large and rapidly growing; it was concentrated at a few large initial points; much of it was high class and very remunerative. With the enormous extension of refrigeration to cover the long-distance movement of fruit and vegetables, a still more powerful encouragement came into play. These latter businesses were highly seasonal. Few roads could afford to maintain highly specialized equipment to care for a business of a few weeks length. But a private company operating all over the country, could utilize its cars first for early vegetables and fruits from the south, then from the middle west or the Oregon-Washington region, and finally in winter for oranges from California or Florida. The number of these cars rapidly increased until by 1903 there were 130,000 in service,--in fact about one-eleventh of all the freight cars in the United States were privately owned. The so-called Armour interests, primarily engaged in the packing business, were by far the largest single concern. The system of payment for the use of these cars consisted of an allowance, based upon the mileage performed. This used to be one cent per mile, loaded and empty, for refrigerator cars. In 1894 a determined effort was made by the carriers to reduce this below the point then reached of three-fourths of a cent per mile. But the extraordinary concentration both of ownership and traffic, rendered it easy for the car companies to defeat the proposition. In the meantime the steady increase in volume of traffic, making whole trainloads possible, together with the growth of very long distance business, made it imperative that these trains be operated at high speed with few stops. This at once enormously enhanced the earning power of each car, as based upon mileage. The performance was often as high as four times that of the ordinary freight cars. Under these new conditions, at the current rate of earnings, a car would pay for itself in three years, besides paying all expenses of maintenance. The burden of these allowances became very great. The situation some years ago is well described by a former member of the Interstate Commerce Commission, as follows:--