Carl Johannes With (December 11, 1877 – June 16, 1923) was a Danish medical doctor and arachnologist, specialising in pseudoscorpions and mites.
With was born in Lemvig to Nicolai Rasmus With and his wife Rasmine Sophie Dorothea With, but was orphaned by the age of five. With married Inge Kiørboe on July 1, 1909, and together they had three children. With died in 1923 in Skibstrup, in the parish of Hellebæk (Helsingør Municipality), while still working on a dissertation on lupus.
Zoological career
After studying at the University of Oxford in 1896, With studied natural history and geography, and in 1904, undertook a research trip to England and in particular, the collections of the British Museum. In 1905, he won the (Schibbye Prize) for his work on Opilioacariformes.
Medical career
With was not confident that zoology could provide a secure future, so he studied medicine, including time at the in Paris. He took part in the Franco–Danish leprosy expedition to the Danish West Indies in 1909, graduated in 1911, and then started to work as a dermatologist at the University Hospital and Municipal Hospital in Copenhagen.