Der Gebrauch des Spektroskopes zu physiologischen und ärztlichen Zwecken.

The first monograph on medical spectroscopy. After Hoppe-Seyler published the first paper on the application of spectroscopy to blood chemistry in 1862 (No. 870), Valentin decided to publish his own contributions to the spectroscopy of blood in this monograph, rather than a journal article.  Digital facsimile from Google Books at this link.

See Frederic L. Holmes, "Crystals and carriers: The chemical and physiological identification of hemoglobin," In No truth except In the details. Essays in honor of Martin J. Klein. Edited By A. J. Kox & Daniel M. Siegel (1995) 191-244.