The subject of this thesis is the development of the Slovene language and the expansion of its terminology in the second half of the 19th century. The first section of the thesis begins with a brief introduction of the historical background, as well as the political and social circumstances of that time. The central section of the thesis examines the translation of the book Das Buch der Natur from the author Friedrich Karl Ludwig Schoedler from German into Slovene, ordered by the Slovene publisher Slovenska matica. Based on historical documents from the Archives of the Republic of Slovenia, the translational approach of the translator Janez Zajec is examined, particularly as regards his translation of Mineralogie und Geognosie, the third part of Schoedlers book Buch der Natur. Furthermore, based on a translation analysis, the translational decisions of Janez Zajec are examined, as well as the extent of his interventions into the German source text. The final section of the thesis examines the contribution of Janez Zajec to the process of Slovene terminology extension by means of introduction of Czech loan words into the Slovene language. A terminology analysis provides the proof of reception and integration of these loan words within the Slovene language and offers insight regarding their further development up to the present day.