If the validity of some particular form of regulation for a particular purpose be conceded, another difficulty arises in determining the proper range and scope of the proposed law. The equal protection of the laws guaranteed by the fourteenth amendment does not demand a mechanical equality of treatment of all persons irrespective of the conditions of their occupation or employment; but this equality is inconsistent with arbitrary or partial discrimination. Ever since the Supreme Court of the United States declared the Illinois anti-trust law unconstitutional, because it made an exception from its prohibitions with reference to agricultural products or live stock in the hands of the producer or raiser,[67] there has been a feeling of uncertainty as to the extent of permissible classification. The tendency of the federal Supreme Court has been on the whole to concede to state legislatures a considerable latitude in the selection of objects of police restraint; but the risk of contest on this ground is a factor to be reckoned with in framing any restrictive legislation. Some of the states, as Illinois, are inclined to apply the principle rather strictly against the singling out by statute of certain groups, when other groups might be liable to similar dangers or evils. The categories which we find mentioned in the American statutes restricting the hours of labor of women, are factories (by this or some other equivalent designation), mechanical establishments (not clearly differentiated from factories), mercantile establishments, laundries, hotels and restaurants. In most of the states having laws on the subject only some of these are covered. No law has as yet undertaken to regulate with particular reference to women either industrial home work or domestic or semi-professional service. Only one state (Oregon) includes the important transportation and transmission employments, especially the telephone and telegraph service, in which so many women are engaged, while Montana confines its restriction to the public telephone service. Up to the present time no law relating to women’s work has been declared unconstitutional by reason of the specification of particular employments; the law sustained by the Supreme Court of the United States applied to manufacturing and mechanical establishments and laundries. It seems reasonable enough to differentiate these employments from those in which there is an element of personal service, such as waiting on customers or rendering direct assistance to the employer, and which are therefore free from the monotonous routine of purely mechanical work. It might be difficult on the other hand to justify the omission of such work as dishwashing or scrubbing in restaurants or hotels. Again, where the restriction applies to employment in mechanical, but not in mercantile establishments, a question might be raised concerning the clerical positions of both classes which are filled by women, and which are