Donne's and Foucault's work was the first biomedical textbook to be illustrated with images made from photomicrographs, in this case daguerreotypes of blood cells. Among its noteworthy images are the first microphotographs of human blood cells and platelets, and the first photographic illustration of Trichomonas vaginalis, the protozoon responsible for vaginal infections, which Donné had discovered in 1836. The text volume of the Cours contains the first description of the microscopic appearance of leukemia, which Donné had observed in blood taken from both an autopsy and a living patient. His observations mark the first time that leukemia was linked with abnormal blood pathology. Foucault, who later achieved fame as a physicist, initally studied medicine, which he abandoned for physics due to an extreme fear of blood. Foucault initially directed his attention to the improvement of Louis Daguerre's photographic processes. For three years he was experimental assistant to Donné in his course of lectures on microscopy.