Wislizenus worked diligently at his practice for six years, even 
taking care of his friend George Engelmann’s patients for a time when 
Engelmann went to Germany to be married. His fascination with the 
West remained compelling, however, and as soon as he could afford 
it, he started on an ambitious trip to observe and record the flora, fauna, 
geology, climate, and topography of northern Mexico and parts of 
California. 
Wislizenus’ timing for this expedition turned out to be extremely 
bad. The explorer reached Mexico just before war broke out between 
that country and the United States. He and other Americans there were 
promptly imprisoned by the Governor of the state of Chihuahua and 
spent several months, in Wislizenus’ words, ‘‘in a very passive situa- 
tion’ that lasted until their release by invading American forces.!4 Upon 
being set free, Wislizenus temporarily joined the army as a surgeon 
and continued his scientific observations. He remained with the army 
until it reached the mouth of the Rio Grande, proceeding from there 
to New Orleans and up the Mississippi to St. Louis. 
The war frustrated Wislizenus’ effort to make a scientifically fo- 
cused tour. Nevertheless, his research and collecting yielded a wealth 
of information and specimens despite the numerous difficulties he faced 
and the changes in plan he was forced to make. The intrepid German 
managed to visit several mines in New Mexico and analyze their ores; 
and he made detailed studies of numerous geological formations, com- 
piled meteorological tables, calculated the elevation of key points along 
his route, and collected an impressive number of previously unknown 
plants. 
At the insistence of Missouri Senator Thomas Hart Benton, the 
United States Senate published Wislizenus’ account of his expedition 
in English in 1848. In addition to Wislizenus’ daily journal entries, the 
book contained maps, meteorological tables, and a ‘‘botanical appen- 
dix’’ written by George Engelmann. '5 This book, unlike the first one 
Wislizenus wrote, was widely appreciated. In fact, it was the most im- 
portant scientific contribution Wislizenus made during his active and 
fascinating life. The explorer Alexander von Humbolt praised and used 
it, for instance, and a German translation was sold in Germany. 
Wislizenus went to Washington to supervise the publication of his 
book in 1848. When he returned to St. Louis, he found there a raging 
Asiatic cholera epidemic. This pestilence was not new to St. Louis. The 
first cholera outbreak occurred in the early 1830s, brought by travellers 
to St. Louis from Pittsburgh and Cincinnati via the Ohio and Mississippi 
rivers. It came again in 1848 when thousands of German immigrants, 
fleeing a European epidemic as well as poor harvests and economic 
malaise in Germany, arrived at the city. '6 
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