This section is from the book "The Constitutional Law Of The United States", by Westel Woodbury Willoughby. Also available from Amazon: Constitutional Law.
The interstate comity clause of the federal Constitution does not compel the several States to grant to resident citizens of the other States immediately upon their entrance into the State the political privileges extended to their own citizens. This the Supreme Court has held from the very beginning and has recently reaffirmed in the case of Blake v. McClung.9 "A State," says the court in that case, "may by rule uniform in its operation as to citizens of the several States, require residence within its limits for a given time before a citizen of another State who becomes a resident thereof shall exercise the right of suffrage or become eligible to office. It has never been supposed that regulations of that character materially interfered with the enjoyment by citizens of each State of the privileges and immunities secured by the Constitution to citizens of the several States. The Constitution forbids only such legislation affecting citizens of the respective States as will substantially or practically put a citizen of one State in a condition of alienage when he is within or removes to another State, or when asserting in another State the rights that commonly appertain to those who are part of the political community known as the People of the United States, by and for whom the Government of the Union was ordained and established."
9 172 U. S. 239; 19 Sup. Ct. Rep. 165; 43 L. ed. 432.
finally, it is to be said, the several States may impose upon non-residents such special limitations and obligations as axe. in aim and effect, not discriminative but reasonably necessary for the protection of their own citizens from fraud, disease, or injury of any sort. Thus, as an example, though the citizens of other States may not be forbidden to sue in the courts of the State, they may be required to give bonds for costs not exacted of residents.1"
In connection with this police power of the States a difficult question is raised as to the constitutionality of laws conditioning the exercise of certain professions,, such as law, medicine, and dentistry upon residence in the State for specified periods of time. There is no question but that the State in the legitimate exercise of its police power may require evidence of good character or sufficient technical attainments of all persons desiring to practice these professions. A certain period of residence in the State may, therefore, possibly be a proper requirement, in order that the applicant's moral character and general attainments may be learned, but it would seem that if this required period be made unnecessarily long, it might be held that non-residents are unduly discriminated against. We have, however, no cases in which this position has been taken.