Later he had a private practice in Kassel, and travelled extensively throughout Europe, particularly Paris, where he collaborated with physicians that included Claude Bernard (1813–1873), Jean-Martin Charcot (1825–1893) and Jean Zuléma Amussat (1796–1856).
In 1840 he made first mention of vasomotor nerves in a treatise titled Physiologisch-pathologische und medicinisch-praktische Untersuchungen über die Spinal-Irritation.
Also, he is remembered for introducing a procedure of serial-section portrayal (thin slicing) of spinal cord specimens for histological study.
Stilling performed the first ovariotomy in Germany, using an extraperitoneal technique that minimized excessive internal bleeding.
This procedure is explained in his paper, Geschichte einer Exstirpation eines krankhaft vergrösserten Ovariums.