In 1898 Oscar Raab, while a student in Tappeiner's laboratory, recognized that paramecia were sensitized to light by the aniline dye, acridine. This finding led to extensive studies by Tappeiner and Jodlbauer and their associates,9,19,-21 and to the introduction of the term "photodynamic action," used by Tappeiner in 1904.
The use of hematoporphyrin in the study of photodynamics came soon after the original studies by Raab. The first study was by Hausmann in 1908. He reported destruction of paramecia and red blood cells and described in detail the symptoms of sensitized mice on exposure to light.6-8 Pfeiffer found the same thing in guinea pigs, and in 1913 Meyer-Betz sensitized himself and reported similar symptoms which lasted two months. During subsequent years, many studies1-4 were carried out using hematoporphyrin hydrochloride prepared according to the classic method of Nencki and Zaleski. However, Schwartz and associates16,17 have found that