112 STUDIES IN IMMUNITY. 



Prom these observations, then, it is easy to realize that Mar- 

 morek'a streptococcus owes its extreme virulence for the rabbit, 



not only to the great rapidity of its development in the body fluids, 

 but particularly to its power to prevent its own engulfment by 

 Leucocytes. It exercises a negative chemiotactic influence on 

 rabbit leucocytes, and this repelling action is characteristic not 

 only of streptococci adapted to the body fluids by origin in them, 

 but also of organisms grown on culture media. 



Indeed, if 0.5 of a cubic centimeter of a culture is injected into 

 the peritoneum of a rabbit that has received G c.c. of bouillon the 

 night before and contains, therefore, numerous leucocytes, the ma- 

 jority of these bacteria remain free and soon become surrounded 

 with an areola. And yet under such conditions the number of 

 bacteria injected is relatively small when compared with the large 

 number of phagocytes. We know, moreover, that the phagocytes 

 present in an exudate caused by injecting bouillon, are very ac- 

 tive and show remarkable phagocytic power for various bacteria. 



In this experiment, however, phagocytosis is not entirely absent; 

 there are always a few cocci that become the prey of cells. If the 

 number of bacteria inoculated is markedly diminished, if, for ex- 

 ample, 0.1 of a cubic centimeter is injected into the prepared peri- 

 toneum of such a rabbit, the number of engulfed bacteria increases; 

 this fact indicates, it would seem, that there are certain cells in 

 this exudate that are particularly active and absorb a certain num- 

 ber of bacteria. But however small may be the dose inoculated, 

 there always remain certain free bacteria whose multiplication 

 rapidly takes place. A previous inoculation of bouillon into the 

 peritoneal cavity increases the number of active leucocytes in the 

 exudate, but will not protect the rabbit against a subsequent 

 inoculation of streptococci even when these organisms are very 

 few in number in proportion to the phagocytes. 



This chemiotactic influence is present, particularly, in young 

 streptococci and is present, most markedly, in organisms under- 

 going active multiplication. It is easy to prove that the strepto- 

 cocci from a three- or four-day-old culture are much less repelling. 

 If even a large dose of such a culture (several cubic centimeters) is 

 injected into the prepared peritoneum of a guinea-pig, active phago- 

 cytosis occurs, and usually of the majority of the organisms 



