Kühne's original work falls into two main groups, the physiology of muscle and nerve, which occupied the earlier years of his life, and the chemistry of digestion, which he began to investigate while at Berlin with Virchow. In 1876, he discovered the protein-digesting enzyme trypsin. He was also known for his research on vision and the chemical changes occurring in the retinaunder the influence of light. Using the "visual purple", described by Franz Christian Boll in 1876, he attempted to make the basis of a photochemicaltheory of vision, but though he was able to establish its importance in connection with vision in light of low intensity, its absence from the retinal area of most distinct vision detracted from the completeness of the theory and precluded its general acceptance. Kühne also pioneered the process of optography, the generation of an image from the retina of a rabbit by applying a chemical processto fix the state of the rhodopsin in the eye. Later, Kühne attempted his technique on the eye of a convicted murderer from Bruchsal, Germany with inconclusive results. He was elected member of the Royal Swedish Academy of Sciences in 1898.
Some notable students
, martyr and national hero of the Philippines, learned physiology under Professor Kühne at the Heidelberg University in 1886. Ida Henrietta Hyde wanted to study physiology under Kühne at the University of Heidelberg on the recommendation of Professor Alexander Goette at Strasbourg. The University accepted her, but Willhelm Kühne refused to allow her in lectures and laboratories. He is reported to have said that he would never allow “skirts” in his classes. However, when a colleague asked him whether, if at the end of the course she could pass the examination, he would grant her the degree, he jokingly replied that he would. And so for six semesters, she had to study physiology independent of the classroom and of hands-on laboratory projects, using only his assistants’ notes and lab sketches. Finally, a four-hour oral examination by Kühne’s academic committee, proved her worthiness. The “Summa Cum Laude” degree, the highest honors, could not go toa woman, so Kühne invented a new phrase: “Multa Cum Laude Superavit" in English meaning “she overcame with much praise.” Hyde completed the PhD at Heidelberg in 1896, the first woman to receive one for this type of work. Kühne recommended her for a position at the Heidelberg-supported research program at the Naples Marine Biological Laboratory in Naples Italy, where she studied the nature and function of salivary glands. She was a life member of this organization, and its secretary from 1897 to 1900.
