390 STUDIES IN IMMUNITY. 



slightest bactericidal action in vitro, but act particularly as stimu- 

 lants to phagocytosis. 



Denys and Leclef * showed that this was the case with anti- 

 streptococcus serum, and Neufeld and Rimpau t later corroborated 

 these findings for the streptococcus and extended them to the 

 pneumococcus. They called these substances, which they supposed 

 to exist in the immune sera and which they believed to act favorably 

 on phagocytosis, bacteriotropins. 



But even before that time Wright, working with Douglas and 

 several other collaborators, had perfected a special technic by which 

 it was possible to study the relations of phagocytes to bacteria during 

 the process of phagocytosis. He demonstrated in the blood and 

 in other body fluids substances which he called opsonins. These 

 substances prepare the bacteria for phagocytosis by becoming fixed 

 upon them. They are, in general, thermolabile, greatly increased 

 in the immune sera, and specific. 



These opsonins, which are considered individual substances by 

 some, are by others believed to be identical with the sensitizers 

 or with the alexin. Recently LevaditiJ with two collaborators, 

 Inmann and Koessler, assumed an intermediate position in that he 

 believes the opsonins of normal serum to be identical with alexin 

 and the opsonins of specific sera to be identical with the sensitizers. 

 Neufeld and Hiine maintain, on the other hand, a distinctive posi- 

 tion for their bacteriotropins. Muir and Martin, || in a series of 

 experiments, using a technic which partially corresponds to that of 

 my experiments (fixation of complement), have shown a marked 

 similarity between alexin and opsonin. 



Let us now consider what our own investigations have taught 

 us. I wish first to report on the character of the opsonins in normal 

 sera. In my first experiments I employed frog leucocytes, since 

 I knew that after three washings with physiological saline solution 

 they lose completely their power of ingesting anthrax bacilli, and 

 that fresh serum will reactivate them by the fixation of the serum 

 opsonin upon the bacteria. Furthermore, I had previously con- 



* La Cellule, 1895. 



t Deutsche med. Woch., 1904, and Zeitschr. f. Hyg. u. Infektionskrank. 1905. 



t C. R. Soc. de Biologic, April and May, 1907. 



Arb. a. d. Kaiserl. Gesundheitsamte, 1907. 



|| Brit. Med. Journal, December, 1906. 



