Reil advanced the doctrine of the life-force as the chemical expression of physiological function. Like Glisson and Hunter, he recognized irritability as a specific property of tissue. He founded the Archiv für die Physiologie, the first journal of physiology. Volume 1 was issued in 3 parts. This first issue of the journal, containing Reil's long paper, appeared in 1795. The volume was complete in 1796, at which time a title page for the complete volume was issued, dated 1796. Reil published 12 volumes of the Archiv für die Physiologie from 1796 to 1813.

Description of the “island of Reil”. This was the first part of the surface of the cerebral hemispheres to be given a name since 1641 (No. 1377.3). See also Reil’s follow-up paper in Arch. Physiol. (Halle), 1809, 9, 136-46; Reil was the editor of this journal, the first periodical devoted to physiology.

The versatile Reil, physician and physiologist, was an early advocate of humane treatment for the insane. He was instrumental in the establishment of the first journal devoted to mental disease – the Magazin für Nervenheilkunde.