Another advantage which these provisions seemed likely to secure to the capital-owning class deserves at least a passing mention. This policy of limiting the amount of municipal indebtedness was adopted at a time when, owing to the rapid growth of urban population, the local monopolies of water, light, transportation, etc., were becoming an important and extremely profitable field for the investment of private capital. The restrictions imposed upon the power of cities to borrow money would retard, if not preclude, the adoption of a policy of municipal ownership and thus enable the private capitalist to retain exclusive possession of this important class of industries. That the constitutional restrictions upon the general indebtedness of cities have retarded the movement toward municipal ownership is beyond question. It is not likely, however, that they will much longer block the way to municipal acquisition of those industries in which private management has proven unsatisfactory, since it may be possible to evade them by resorting to the device of a _special fund_. The same line of argument which has been accepted by the courts as supporting the constitutionality of the special fund for local improvement purposes is no less applicable to special debts incurred for the purchase of revenue-producing public utilities, such as water works, lighting plants and street railways. Under this arrangement, however, the city must not assume any responsibility for the payment of the capital borrowed, the creditors advancing the purchase price or cost of construction, looking solely to the earnings under municipal operation for the payment of both principal and interest. It may be doubted whether the courts in permitting cities to employ the special fund in relation to local improvements realized its possibilities in the direction of municipal ownership.[165]