According to the view we take of the case, it is not necessary to inquire into the special equities set forth in the bill and relied upon in the argument for complainant to show that this record presents a case for the interposition of a federal court, for the purpose of restraining the assessment or collection of a state tax. The primary and fundamental ground on which the maintenance of such a suit rests is the unlawfulness of the tax against which relief is sought, or, in other words, the invalidity or unconstitutionality of the legislative act under the authority of which the tax is imposed. It is true that this ground is not in itself sufficient. But when the illegality of the tax, or the invalidity or unconstitutionality of the legislative act under which it is imposed, is established, it becomes necessary to go further, and make out a case that can be brought under some recognized head of equity jurisdiction,—such as that the collection of the tax sought to be restrained may entail a multiplicity of suits, or cause some other irreparable injury, as, for instance, the ruin of complainant's business, or, where the property is real estate, throw a cloud upon the title of the complainant. Shelton v. Platt, 139 U. S. 591, 594, 11 Sup. Ct. Rep. 646; Allen v. Car Co., 139 U. S. 658, 661, 11 Sup. Ct. Rep. 682.

It is contended in behalf of the complainant (1) that the statute of Missouri, under the provisions of which the tax sought to be restrained is levied, imposes a tax upon interstate commerce, and to that extent is forbidden by the constitution of the United States, and is therefore void; (2) that the act denies to the complainant the equal protection of the laws of the state of Missouri, and is therefore void by reason of its being violative of the fourteenth amendment of the constitution of the United States; and (3) that the act is not uniform and equal in its operation, and is void by reason of its repugnance to section 3 of article 10 of the constitution of the state of Missouri.

We do not think that these propositions, taken in connection with the averments of the bill, present any ground justifying the interposition of a court of equity to enjoin the collection of the tax imposed by the statute in question. The first proposition—that the statute imposes a tax upon interstate commerce, and is therefore violative of what is known as the commercial clause of the constitution—is unsound. It is well settled that a state cannot lay a tax upon interstate commerce in any form, whether by way of duties laid on the transportation of the subjects of that commerce, or the receipts derived from that transportation, or on the occupation or business of carrying it on, for the reason that such taxation is a burden on that commerce, and amounts to a regulation of it which belongs to congress. Lyng v. Michigan, 135 U. S. 161, 10 Sup. Ct. Rep. 725; Leloup v. Port of Mobile, 127 U. S. 640, 8 Sup. Ct. Rep. 1380; Telegraph Co. v. State Board, 132 U. S. 472, 10 Sup. Ct. Rep. 161; McCall v. California, 136 U. S. 104, 10 Sup. Ct. Rep. 881; Railroad Co. v. Pennsylvania, 136 U. S. 114, 10 Sup. Ct. Rep. 958. The question on this branch of the case, therefore, is: Was the business of this express company in the state of Missouri, on the receipts from which the tax in question was assessed under this act, interstate commerce? The allegation of the bill is very positive that in the prosecution of its business as an express company the complainant is engaged, in part, in the transportation of goods and other property between the states of Nebraska, Kansas, Texas, and other states of the Union, and the state of Missouri, and also in the business of carrying goods between different points within the limits of the state of Missouri. The question of this point, therefore, is narrowed down to the single inquiry whether the tax complained of in any way bears upon or touches the interstate traffic of the company, or whether, on the other hand, it is confined to its intra-state business. We think a proper construction of the statute confines the tax which it creates to the intra-state business, and in no way relates to the interstate business of the company. The act in question, after defining in its first section what shall constitute an express company, or what shall be deemed to be such in the sense of the act, requires such express company to file with the state auditor an annual report 'showing the entire receipts for business done within this state of each agent of such company doing business in this state,' etc., and further provides that the amount which any express company pays 'to the railroads or steam boats within this state for the transportation of their freight within this state' may be deducted from the gross receipts of the company on such business; and the act also requires the company making a statement of its receipts to include, as such, all sums earned or charged 'for the business done within this state,' etc. It is manifest that these provisions of the statute, so far from imposing a tax upon the receipts derived from the transportation of goods between other states and the state of Missouri, expressly limit the tax to receipts for the sums earned and charged for the business done within the state. This positive and oft-repeated limitation to business done within the state—that is, business begun and ended within the state evidently intended to exclude, and the language employed certainly does exclude, the idea that the tax is to be imposed upon the interstate business of the company. 'Business done within this state' cannot be made to mean business done between that state and other states. We therefore concur in the view of the court below that it was not the legislative intention, in the enactment of this statute, to impinge upon interstate commerce, or to interfere with it in any way whatever; and that the statute, when fairly construed, does not in any manner interfere with interstate commerce.

The second and third propositions stated above are reducible to the single contention that the act in question violates the requirements of uniformity and equality of taxation prescribed by the constitution of Missouri, and thereby denies to the complainant the equal protection of the laws of the state which the fourteenth amendment to the constitution guaranty shall not be abridged by state action.

This court has repeatedly laid down the doctrine that diversity of taxation, both with respect to the amount imposed, and the various species of property selected either for bearing its burdens or for being exempt from them, is not inconsistent with a perfect uniformity and equality of taxation in the proper sense of those terms; and that a system which imposes the same tax upon every species of property, irrespective of its nature or condition or class, will be destructive of the principle of uniformity and equality in taxation, and of a just adaptation of property to its burdens.

The rules of taxation in this respect were well stated in the opinion of the court, delivered by Mr. Justice BRADLEY, in Railroad Co. v. Pennsylvania, 134 U. S. 232, 237, 10 Sup. Ct. Rep. 533, as follows: 'The provision in the fourteenth amendment, that no state shall deny to any person within its jurisdiction the equal protection of the laws, was not intended to prevent a state from adjusting its system of taxation in all proper and reasonable ways. It may, if it chooses, exempt certain classes of property from any taxation at all, such as churches, libraries, and the property of charitable institutions. It may impose different specific taxes upon different trades and professions, and may vary the rates of excise upon various products. It may tax real estate and personal property in a different manner. It may tax visible property only, and not tax securities for payment of money. It may allow deductions for indebtedness, or not allow them. * * * It would, however, be impracticable and unwise to attempt to lay down any general rule or definition on the subject that would include all cases. They must be decided as they arise. We think that we are safe in saying that the fourteenth amendment was not intended to compel the state to adopt an iron rule of equal taxation. If that were its proper construction, it would not only supersede all those constitutional provisions and laws of some of the states whose object is to secure equality of taxation, and which are usually accompanied with qualifications deemed material, but it would render nugatory those discriminations which the best interests of society require, which are necessary for the encouragement of needed and useful industries, and the discouragement of intemperance and vice, and which every state, in one form or another, deems it expedient to adopt.'

In the case of Insurance Co. v. New York, 134 U. S. 594, 606, 607, 10 Sup. Ct. Rep. 593, the court, speaking through Mr. Justice FIELD, said: 'But the amendment [the fourteenth] does not prevent the classification of property for taxation—subjecting one kind of property to one rate of taxation, and another kind of property to a different rate—distinguishing between franchises, licenses, and privileges, and visible and tangible poperty, and between real and personal property. Nor does the amendment prohibit special legislation. Indeed, the greater part of all legislation is special, either in the extent to which it operates, or the objects sought to be obtained by it; and, when such legislation applies to artificial bodies, it is not open to objection if all such bodies are treated alike under similar circumstances and conditions, in respect to the privileges conferred upon them, and the liabilities to which they are subjected. Under the statute of New York all corporations, joint-stock companies, and associations of the same kind, are subjected to the same tax. There is the same rule applicable to all, under the same conditions, in determining the rate of taxation. There is no discrimination in favor of one against another of the same class;' citing a long list of authorities.

The contention of the complainant, however, in this connection, is that the rule of uniformity and equality of taxation is destroyed by the arbitrary discrimination involved in the definition of what shall be taxed under the act, imposing upon certain persons or associations taxes from which other persons or companies of precisely the same kind, doing exactly the same kind of business, under exactly the same conditions, are exempt. In other words, the contention is that the act of the legislature arbitrarily defines what shall constitute an express company, and then lays a tax upon its business, while at the same time it permits the same kind of business to be done by any person or company not embraced within the class thus defined, without being subject to any tax at all. It is said that the act, by the very terms of its definition, restricts the tax to persons or corporations who carry on the business of transportation on contracts for hire with railroad or steam-boat companies doing business within the state, and that it permits any person or company that may be so fortunate as to own its own means of transportation to go free from any such tax; that is to say, an express company that engages for hire a railroad or steam-boat company to transport its merchandise must pay a tax for the privilege of doing business, while the railroad or steam-boat company, owning its own means of transportation, might, in connection with the business for which it was primarily chartered, engage in the express business without paying any tax whatever on the privilege of carrying on such express business. It is strenuously argued, therefore, that this is an unjust discrimination against the express companies defined by the act, and in favor of other companies or persons that may, in connection with their primary or original business, engage in the express business, or that may carry on a separate express business, owning their own means of transportation.

The fallacy of this argument lies in the assumption that the definition of what shall constitute an express company excludes from the classification companies which are as much engaged in the business, or as much under the same conditions, as are those which, under the definition, are subject to the tax.

The legislation in question cannot be considered as invidiously discriminating against the express companies defined by it, and in favor of other companies or persons that may carry express matter on certain other conditions or under different circumstances. There is an essential difference between express companies defined by this act and railroad or steam-boat companies or other companies that own their own means of transportation. The vital distinction is this: Railroad companies pay taxes on their road-beds, rolling stock, and other tangible property as well as, generally, upon their franchise; and steam-boat companies likewise pay a tax upon their tangible property. This tax is not necessarily an ad valorem tax at the same rate as is paid on other private property in the state belonging to individuals. Generally, indeed, it is not, but is often determined by other means and at different rates, according to the will of the state legislature. Kentucky Railroad Tax Cases, 115 U. S. 321, 337, 6 Sup. Ct. Rep. 57. On the other hand, express companies, such as are defined by this act, have no tangible property, of any consequence, subject to taxation under the general laws. There is therefore no way by which they can be taxed at all, unless by a tax upon their receipts for business transacted. This distinction clearly places express companies defined by this act in a separate class from companies owning their own means of transportation. They do not to business under the same conditions or under similar circumstances. In the nature of things, and irrespective of the definitive legislation in question, they belong to different classes. There can be no objection, therefore, to the discrimination made as between express companies defined by this act and other companies or persons incidentally doing a similar business by different means and methods, in the manner in which they are taxed. Their different nature, character, and means of doing business justify the discrimination in this respect which the legislature has seen fit to impose. The legislation in question does not discriminate between companies brought within the class defined in the first section; and such companies being so entirely dissimilar, in vital respects, as regards the purposes and policy of taxation, from railroad companies and the like owning a large amount of tangible and other property subject to taxation under other and different laws, and upon other and different principles, we do not see how, under the principles of the many decisions of this court upon the subject, it can be held violative either of the fourteenth amendment of the constitution of the United States, or of the provision in the constitution of Missouri relating to equality and uniformity of taxation. See Barbier v. Connolly, 113 U. S. 27, 5 Sup. Ct. Rep. 357; Soon Hing v. Crowley, 113 U. S. 703, 5 Sup. Ct. Rep. 730; Dent v. West Virginia, 129 U. S. 114, 9 Sup. Ct. Rep. 231; Railroad Co. v. Humes, 115 U. S. 512, 6 Sup. Ct. Rep. 110; City v. Weber, 44 Mo. 547; Insurance Co. v. Com., 85 Pa. St. 513; State v. Welton, 55 Mo. 288.

The opinion of the court below on this branch of the case is elaborately argued, and is conclusive. We concur in the reasoning of it, as well as in the language employed, and refer to it as a correct expression of the law upon the subject.

Decree affirmed.