Cost of service, while unsound as a sole reliance, nevertheless affords an important check upon the value of service principle. Without it there is always grave danger that traffic managers, seeking to enlarge their revenues, may push rates unreasonably high. At first sight it would appear as if this could not occur, inasmuch as an inordinately high rate would immediately reduce the volume of business offered. It is constantly alleged by railway men that this must of necessity occur. And it would indeed follow, were it not that the incidence of the rate is rarely upon the actual shipper. He merely pays it, and at once shifts it to the consumer. For low-grade or staple goods like cement or kerosene, where transportation charges form a large part of the total cost of production, it is conceivable that higher freight rates might so far increase the price as to check consumption. Five cents a hundredweight higher freight means $1.25 per 1,000 ft. added to the price of soft lumber, $2 to hard lumber; three cents per bushel added to the price of wheat, and $1 to the ton of pig iron or coal. Such substantial additions might readily reduce the demand. Yet even this would not be true of necessities of life like anthracite coal or sugar, on which latter the freight rate amounts to about one-half cent per pound. Is five cents a barrel added to the price of flour likely to decrease the consumption of that staple commodity? Yet the enhancement of railway revenues would indeed be enormous from such an increase of freight rates. For these necessities of life, an increased freight rate might become an actual charge upon the people, without reducing their consumption, like a tax upon salt. Only upon goods the use of which might be freely lessened, would higher freight rates be reflected in a corresponding decline in the volume of business. Moreover, with all high grade traffic, the value of service principle fails utterly by itself alone to prescribe the upper level of a reasonable charge. Competent testimony is ample upon this point. Thus from the commissioner of the Trunk Line Association;[143] "The tonnage of the higher class articles is an extremely difficult matter for transportation companies to increase or decrease.... In that class of articles the carrier can do but little to increase the transportation." And the reason in part lies in the almost immediate diffusion of the burden in the processes of distribution. That no complaints are made--a defence often brought forward for higher rates--proves by itself the uncertain incidence of the burden imposed.