130 IMMUNITY AND INFECTION 



the phagocytic cells. These enzymes are of two kinds: macrocytase, 

 present in the macrophages, and microcytase, found in the micro- 

 phages. 1 Van de Velde, 2 Buchner, 3 Hahn, 4 and Bordet 5 have demon- 

 strated such endo-enzymes. The solution of bacteria engulfed in leuko- 

 cytes can be shown by appropriate staining methods; the organisms 

 gradually lose their ability to take up stain and eventually disappear. 



At this stage of the development of the phagocytic theory of immu- 

 nity, the important part played by the blood serum in preparing bac- 

 teria for phagocytosis was prominently set forth in the investigations 

 of Wright and Douglas, 6 although foreshadowed by the excellent and 

 comprehensive observations of Denys and LeClef 7 and Neufeld and 

 Rimpau. 8 Wright and Douglas showed that leukocytes, freed care- 

 fully from adherent serum by washing with salt solution, would not 

 engulf bacteria, or, at least, but slowly. The addition of serum from 

 a normal or immunized animal caused active phagocytosis to take 

 place. The substances in the blood serum which prepare bacteria 

 for engulf ment by leukocytes were called "opsonins" by Wright and 

 Douglas: the immune opsonins which are specifically increased in 

 immunized animals are almost certainly identical with the substances 

 called bacterial tropins by Neufeld and Rimpau. That the opsonic 

 substances of the serum act primarily upon the bacteria rather than 

 upon the leukocytes was clearly shown by the observations of Hektoen 

 and Reudiger. 9 Streptococci suspended in plasma, blood serum or 

 defibrinated blood were engulfed by leukocytes. Leukocytes, washed 

 free from serum or plasma, were without phagocytic action upon the 

 same bacteria. If the streptococci, however, were allowed to stand 

 in contact with serum, plasma, or defibrinated blood for a short time 

 at 37 (a much longer exposure at to 4 C. was necessary), then 

 washed free from adherent serum or plasma, and exposed to washed 

 leukocytes, active phagocytosis took place. 



The present tendency is to ascribe to phagocytosis an important 

 part both in the destruction of many kinds of invading bacteria and 

 in the removal of alien or abnormal cells as well. The importance 



1 For a detailed discussion of leukocytic enzymes, see Opie, Jour. Exp. Med., 1905, 

 viii, 410. 



La Cellule, x, 2; Cent. f. Bakt., 1898, xxxiii, 692. 



Miinchen. med. Wchnschr., 1894, 718. 



Arch. f. Hyg., 1895, xxviii, 312. 



Ann. Inst. Past., 1895, ix, 398. 



See Wright, Studies in Immunization, 1909, Constable. 



La Cellule, 1895, xi. 



Deutsch. med. Wchnschr., 1904, 1458. 

 9 Jour. Inf. Dis., January, 1905, ii, No. 1. 



