On 17 June 1878, he had an important audience with Victor Hugo, where he pledged himself to France as his home country to great public aclaim.

Loewenthal took an active part in the conference which opened in Berne in 1883 to draft and vote on a draft "convention to establish a General Union for the Protection of the Rights of Authors in Literary and Manuscript Works", a conference whose work would lead to the International Convention of Berne in 1886.

He took part in research on cholera with Robert Koch, and continued work with Victor André Cornil in Paris.

There, Lowenthal was mentioned in dispatches to a packed house by the Journal Officiel from 9 August that year, in the following terms: French: Monsieur le Docteur Wilhelm Loewenthal, ancien délégué général pour l'Allemagne, actuellement délégué correspondant à Lausanne (Suisse), fait une communication sur les connaissances actuelles de la science relativement aux microbes.

Wilhelm Lowenthal, lately living in Germany, is actually writing to us from Lausanne, in Switzerland, about things he knows about the science of microbes.

In 1886, he received 16 certificates in medicine from the University of Heidelberg, equivalent to a French baccalaureat or roughly an English Bachelor of Science.

This allowed him to go on a mission to Tonkin, at the request of the colonial administration, to experiment with “the immediate parasiticidal action of Salol on cholera microbes”.

The colony was under the control of the Jewish Colonization Association (JCA), run by Baron Maurice de Hirsch.