The declaration discloses a case within the jurisdiction of the court--a controversy between citizens of different States. The plea in abatement, impugning these jurisdictional averments, was waived when the defendant answered to the declaration by pleas to the merits. The proceedings on that plea remain a part of the technical record, to show the history of the case, but are not open to the review of this court by a writ of error. The authorities are very conclusive on this point. Shepherd _v._ Graves, 14 How., 505; Bailey _v._ Dozier, 6 How., 23; 1 Stewart, (Alabama,) 46; 10 Ben. Monroe, (Kentucky,) 555; 2 Stewart, (Alabama,) 370, 443; 2 Scammon, (Illinois,) 78. Nor can the court assume, as admitted facts, the averments of the plea from the confession of the demurrer. That confession was for a single object, and cannot be used for any other purpose than to test the validity of the plea. Tompkins _v._ Ashley, 1 Moody and Mackin, 32; 33 Maine, 96, 100. There being nothing in controversy here but the merits, I will proceed to discuss them. The plaintiff claims to have acquired property in himself, and became free, by being kept in Illinois during two years. The Constitution, laws, and policy, of Illinois, are somewhat peculiar respecting slavery. Unless the master becomes an inhabitant of that State, the slaves he takes there do not acquire their freedom; and if they return with their master to the slave State of his domicil, they cannot assert their freedom after their return. For the reasons and authorities on this point, I refer to the opinion of my brother Nelson, with which I not only concur, but think his opinion is the most conclusive argument on the subject within my knowledge. It is next insisted for the plaintiff, that his freedom (and that of his wife and eldest child) was obtained by force of the act of Congress of 1820, usually known as the Missouri compromise act, which declares: "That in all that territory ceded by France to the United States, which lies north of thirty-six degrees thirty minutes north latitude, slavery and involuntary servitude shall be, and are hereby, _forever prohibited_." From this prohibition, the territory now constituting the State of Missouri was excepted; which exception to the stipulation gave it the designation of a compromise. The first question presented on this act is, whether Congress had power to make such compromise. For, if power was wanting, then no freedom could be acquired by the defendant under the act.