Opinion by
Smith, J.,The power of the legislature to classify the cities of the commonwealth, and to legislate for each class separately, is too well settled to be questioned. This power is based on “ a necessity springing from manifest peculiarities, clearly distinguishing those of one class from each of the other classes, and imperatively demanding legislation for each class', separately, that would be useless and detrimental to the others Ayars’s Appeal, 122 Pa. 266; Weinman v. Railway Co., 118 Pa. 192; McCarthy v. Com., 110 Pa. 243. The proper basis of such classification is population, and this is the only legitimate basis for the classification of cities and counties : Wheeler v. Philadelphia, 77 Pa. 338; Kilgore v. Magee, 85 Pa. 401; Com. v. Patton, 88 Pa. 258; Scowden’s Appeal, 96 Pa. 422.
Not only does classification rest on the single element of population, but the legislation based on classification is limited in scope. It is only “for the purposes of legislation regulating their municipal affairs, the exercise of certain corporate powers, *69and having respect to the number, character, powers and duties of certain officers thereof” (Act of June 25,' 1895, sec. 1, P. L. 275), .that the legislature has divided cities into three classes. Legislation for any of these classes must relate to a subject within the purposes of classification as thus defined; to the organization and administration of the city government, to the regulation of municipal affairs, and of matters under municipal control, to the number, character, powers and duties of the officers employed in such affairs, and to the exercise, generally, of the corporate powers vested in the municipality; and it must apply to all cities of the designate^, class. If it relates to subjects not included in the purposes of classification, or excludes any city within the class mentioned, it falls within the constitutional prohibition of local or special legislation, and is void : Weinman v. Railway Co., supra; Ayars’s Appeal, supra; Ruan Street, 132 Pa. 257; Wyoming Street, 137 Pa. 494; Scranton v. Whyte, 148 Pa. 419; Chalfant v. Edwards, 173 Pa. 246; Lloyd v. Smith, 176 Pa. 213; Blankenburg v. Black, 200 Pa. 629. In the cases hereinbefore referred to, and the authorities therein cited, will be found illustrations of legislation both within the purposes of classification and outside those purposes.
Though classification is based on necessity, this is not to be understood as an absolute necessity, admitting of no alternative, but as a relative necessity, involving merely great and manifest public advantage or convenience. Since the conditions in a city of one million inhabitants demand regulations, on many subjects, that would be needless or burdensome in a city of ten thousand, the necessity for a classification between the extremes of population is unquestionable. And since many of the municipal regulations required in a city of either of these two classes would be unsuited to cities having a population largely Below that of the former yet much above that of the latter, there is an equal necessity, arising from considerations of public convenience, for an intermediate class. Proceeding on this view, the legislature, by the Actof May 23, 1874, P. L. 230, divided ,the cities of the commonwealth into three classes, and this classification was sustained by the Supreme Court, as being within the spirit if not within the letter of the constitution: Wheeler v. Philadelphia; Kilgore v. Magee, supra. The Act *70of April 11,1876, P. L. 20, amended, this classification by dividing cities into five classes ; and the Act of May 24, 1887, P. L. 204, made a division into seven classes. In 1889, these classifications were pronounced unconstitutional, as not warranted by any necessity. “ As to the number of classes created, the act of 1874 appears to have covered the entire ground of classification. It provided for all existing as well as every conceivable prospective necessity.” As to the act of 1887, “ The charter powers of the fourth to seventh classes, inclusive, are precisely similar. There is nothing to prevent the last four classes from being included in the third class, established by the act of 1874. Their needs are all so similar that no charter power required for either of them would be unnecessary or detrimental to any of the others: ” Ayars’s Appeal, supra. The Acts of May 8, 1889, P. L. 133, and June 25, 1895, P. L. 275, again fixed the division into three classes, and each act increased the minimum population of each class. The validity of the present classification, under the constitution, must be regarded as firmly established.
It only remains to determine whether the provisions of the Act of June 7, 1901, P. L. 493, now under consideration, are within the purposes .for which cities are legally classified.
Among subjects of municipal concern, none is more important than the preservation of the public health. The prevention of disease by municipal authority is as clearly a municipal function as the prevention of its spread by quarantine or otherwise. Legislation designed to guard against disease, by establishing or promoting the sanitary conditions most favorable to health, must be deemed within the purposes for which the classification of cities is permitted. The regulation of the municipal affairs of the several classes of cities, therefore, must be held to embrace adequate statutory provisions on this subject. There is no apparent reason why the established classification, with respect to other municipal purposes, should not be maintained as to this. The differences in local needs and conditions affecting this matter, among the three classes of cities, are as obvious as those relating to various other purposes for which the power to legislate for a class is undeniable. And among sanitary conditions, few are more important than a sys*71tern of plumbing, house drainage, and sewerage which shall be safe and sufficient at every point. The establishment and maintenance of such a system requires expert knowledge and skill. Provisions calculated to insure that the work involved in the system shall be performed only by competent persons, that the materials used shall be suitable, and the methods emplojmd adequate, obviously fall within ttye regulation of municipal affairs. The statutory provisions now under consideration clearfy meet the constitutional requirements, and must be declared valid.
The provisions of other acts on this skbject, in relation to other classes of cities, afford no guide in deciding as to the constitutionality of those now before us. That they are different from those here under consideration is nothing'to the purpose. The classification of cities is based on differences of conditions and needs, implying corresponding differences in the' legislation providing for them. Classification would be meaningless and nugatory if nevertheless uniformity in legislation were inquired. It is for the legislature to determine what differences in conditions and needs justify differences in municipal regulations, subject to judicial review as to whether the end is true classification, or special legislation, disguised as classification: Lloyd v. Smith, 176 Pa. 213. If the legislative provisions are directed to any of the purposes for which classification is designed, their fitness for the purpose is to be determined by the legislature, and not by the courts.
The suggestion that the 70th section of the act makes the director of public safety the sole judge in all disputes arising under the act is evidently based on a misapprehension. That section 'merely relates to differences regarding construction, and in effect makes the director the arbiter between the -contending parties, — substantially as differences respecting various constructions are, by contract, to be determined by the supervising architect. Section 71 provides for a judicial trial when a penalty'is involved, and the present appeal arises from such a trial.
The act of 1901 follows, in purpose and plan, the Act of June 7, 1895, P. L. 135, and extends its principal provisions. This court has sustained the latter act on a similar branch of its main subject, as a proper exercise of the police power of the *72state or municipal purpose, when assailed on the ground of unconstitutionality, in Shenck v. Pittsburg Club, 11 Pa. Superior Ct. 84. The Supreme Court having refused an appeal from our decision in that case, we give a like construction to the act of 1901.
Judgment affirmed.