In 1803 he was appointed personal physician to Frederick Augustus, and from 1815 served in Dresden as a trainer of Saxon military doctors. For health reasons, he left academic work in 1822, retiring to a private practice, from which he concentrated on botanical studies.
Kreysig is largely known for his work with cardiological diseases. In 1815 he explained inflammatory processes associated with endocarditis.[2] With physician Ernst Ludwig Heim (1747–1834), the "Heim-Kreysig sign" is named, which in adherent pericardium, an in-drawing of the intercostal space occurs, synchronous with the cardiac systole.[3]
Aristotelis de soni ed vocis humanae natura atque ortu theoria cum recentiorum decretis comparata, Leipzig 1793
De peripneumonia nervosa s. maligna commentatio, Leipzig 1796
Neue Darstellung der physiologischen und pathologischen Grundlehren (New representation of physiological and pathological basic teachings), Leipzig 1798–1800
Abhandlung über das Scharlachfieber, nebst Beschreibung einer sehr bösartigen epidemischen Frieselkrankheit, welche im Februar 1801 in Wittenberg herrschte (Essay on scarlet fever, etc.), Leipzig 1802
Die Krankheiten des Herzens, systematisch bearbeitet und durch eigenen Beobachtungen erläutert (Diseases of the heart, etc.), Berlin (1814–1817, four volumes)
System der praktischen Heilkunde, usw (System of Practical Medicine); Leipzig und Altenburg, (1818–1819, two volumes)
Über den Gebrauch der Mineralwässer von Karlsbad, Ems, usw (On the usage of mineral waters of Karlsbad, Ems, etc.), Leipzig 1825