Wislizenus studied medicine at the University of Jena in 1828, and later at Göttingen and Würzbürg. He was a member of the "Burschenschaft," but escaped arrest when that was broken up by the authorities. He followed his friend and teacher, the great clinician Schoenlein, to Zürich and there joined an expedition to aid Mazzini in his struggle against Austrian rule; but the Swiss troops disarmed them on the border so he was forced to return to his studies.
Wislizenus graduated in Zürich in 1834 and soon sailed for New York, where he began to practise his profession in 1835. Here he remained two years writing constantly for the German papers of the city. He then went west in 1837 and joined some of his fellow-exiles who had settled in St. Clair County, Illinois. In 1839 he came to St. Louis and immediately seized an opportunity to accompany an expedition of the St. Louis Fur Company for trading with the Indians. He thus went far into the Northwestern country towards the source of the Green Elver in the Wind River Mountains. When the expedition started to return he joined a band of Flat-head and Nez Percé Indians. He thus crossed the Rocky Mountains to Utah and went as far as Fort Hall, the most southern post of the English trading company. Here he could find no guide to take him to California, so he returned; crossing the Green and the south fork of the Platte, he followed the Arkansas to Missouri. During this trip he had no facilities for making scientific observations and collections, so it was wholly without any such results.
On his return to St. Louis in 1840 he resumed his practise of medicine He was identified with early efforts towards the establishment of an Academy of Science, and aided Dr. Engelmann in his efforts to found a botanic garden, and was an earnest worker in the Western Academy of Science. He soon gained a lucrative practice, but as soon as the opportunity offered he was again in the field. He joined a trading expedition to Mexico, well equipped this time with instruments and apparatus for scientific work. In Santa Fé they first learned of the war between Mexico and the United States, but Wislizenus obtained a pass and proceeded to Chihuahua, where he with other Americans was seized and imprisoned. He was sent to a small mountain town of the interior and there had ample opportunity to carry on his collecting and observations in the neighborhood during the winter. Upon the arrival of Col. Doniphan's troops in the spring he was released and accompanied them in a professional capacity until their disbanding at New Orleans in 1847, when he returned to St. Louis.
Senator Thomas H. Benton became interested in him and his experiences in Mexico, and finally was the cause of his being summoned to Washington and being requested to prepare for publication the results ot his investigations. His resulting "Memoir of a Tour to Northern Mexico in 1846 and 1847" was considered important enough so that the senate ordered 5,000 copies printed for distribution. This publication