The principal obstacle to the successful operation of disability insurance has been the difficulty experienced in its administration--largely on account of the impracticability of closely defining permanent or total disability. With almost every revision of the constitutions changes were made in the definition of the term "disability." Strict construction of the law by the executive officials led to dissatisfaction and often to appeals from their decisions to the insurance committees, or to the boards of trustees.[62] During the early years disability claims were often presented through subordinate officials, who were either unable to interpret the laws aright, or were unwilling to assume the responsibility of pronouncing the claims illegal. The Engineers, after a period of thirty-two years, in 1898 adopted a satisfactory definition of total disability: "Any member of this Association losing by amputation a hand at or above the wrist joint; a foot at or above the ankle joint; or sustaining the total and permanent loss of sight in one eye or both eyes, shall receive the full amount of his insurance."[63] Similar definitions of disability have been worked out by the other railway organizations. The Conductors add to this "total loss of the sense of hearing." The Switchmen include "the loss of four fingers of one hand, at or above the second joint." Disability, as defined by the Letter Carriers, means inability, because of sickness or accident, to perform the regular duties of a letter carrier.[64] [Footnote 62: Proceedings of the Nineteenth Annual Session of the Order of Railway Conductors of America, 1887 (n.p., n.d.), p. 69.] [Footnote 63: Constitution, 1899 (Cleveland, 1898), Art. 28.] [Footnote 64: Constitution of the Letter Carriers of the United States, 1905, Art. 13, in The Postal Record, Vol. 19, No. 1, p. 3.]