Elsewhere in this treatise it is pointed out that, to a certain extent, the State's right of taxation may, in return for a substantial consideration, be parted with.5 When thus parted with, the undertaking not to exercise the right in the manner specified constitutes a contract, the obligation of which is impaired by a subsequent law authorizing its exercise. The clause thus operates as a limitation upon the taxing power of the State. As to the police powers of the State, as will be presently shown, the rule is otherwise. No State, it has been held, may validly contract not to exercise in the future a contract which is necessary to the health, safety, comfort, or morality of its citizens.

3 Section 462. In Bronson v. Kinzie et al. (1 How. 311; 11 L. ed. 143). the court say: "If the laws of the State passed afterwards had done nothing more than change the remedy upon contracts of this description, they would be liable to no constitutional objection. For undoubtedly, a State may regulate at pleasure the modes of proceeding in its courts in relation to past contracts as well as future. It may, for example, shorten the period of time within which claims shall be barred by the statute of limitations. It may, if it thinks proper, direct that the necessary implements of agriculture, or the tools of the mechanic, or articles of necessity in household furniture, shall, like wearing apparel, not be liable to execution on judgments. . . . Although a new remedy be deemed less convenient than the old one, and may in some degree render the recovery of debts more tardy and difficult, it will not follow that the law is unconstitutional. Whatever belongs merely to the remedy may be altered according to the will of the State, provided the alteration does not impair the obligation of the contract." Citing Green v. Biddle, 8 Wh. 1; 5 L. ed. 547.

4 Watson v. Mercer, 8 Pet. 88; 8 L. ed. 876.

5 Section 503.