STUDY OF ANTISTREPTOCOCCUS SERUM. 107 



occurs. The streptococci being in too small numbers are engulfed 

 before they have time to adapt themselves to the medium, and 

 acquire their intense repelling property for leucocytes. Certain 

 ones among them, to be sure, resist and remain free relatively longer 

 than the others. But as their number is inconsiderable in propor- 

 tion to the cells present they finally encounter leucocytes which are 

 so vigorous that they yield to them. The totality of the strepto- 

 cocci injected are eventually contained within the cells. The 

 guinea-pig recovers without any further trouble. 



We have already mentioned that the streptococci that are able 

 to protect themselves against the attack of the guinea-pig leucocytes 

 are surrounded by an areola which takes a peculiar stain. We 

 may further note that in those experiments in which a sublethal 

 dose of streptococci is employed the more resistant micro-organ- 

 isms, that is, those last to be engulfed, are also usually those with the 

 most marked areola. 



The condition necessary for a fatal infection. — In order that 

 streptococci injected into the peritoneum of the guinea-pig may 

 produce a fatal infection the following condition must be satis- 

 fied; when phagocytosis by the rare leucocytes begins, the strepto- 

 cocci should be in sufficient quantity to permit the more virulent 

 of them to remain outside the cells long enough to become accus- 

 tomed to the chemical composition of the exudate so that they 

 and their descendants may acquire to the highest degree the faculty 

 of remaining free amid the increasing leucocytes. It would follow, 

 then, that if we inject a fatal dose of streptococci, not into a normal 

 intraperitoneal cavity where the cells at first are few and little 

 adapted to phagocytosis, but into a peritoneal cavity rich in vigor- 

 ous phagocytic cells capable of bringing about a rapid engulfing, 

 the bacteria will not have the necessary time for adaptation and 

 for increasing their resistance. This, indeed, is what happens. If 

 the number of active phagocytes in the peritoneal cavity of a guinea- 

 pig is increased by a previous injection of bouillon, a dose of strepto- 

 cocci equal to at least twice the ordinary minimal lethal dose may be 

 injected without fatal effect.* We shall not consider such an experi- 

 ment for the moment, but shall take it up again when we come to 



* The amount that can safely be injected naturally has its limits. If as much 

 as 1.5 or 2 c.c. is given, phagocytosis is incomplete, even in a prepared guinea-pig. 



