STUDY OF ANTISTREPTOCOCCUS SERUM. 115 



two animals : guinea-pig leucocytes are much less sensitive than rabbit 

 leucocytes to the repelling action of the streptococcus. As much as 

 0.5 of a cubic centimeter of a young culture of streptococcus or 

 even more is rapidly taken up in the peritoneal cavity of a guinea- 

 pig previously injected with bouillon. The same amount of strepto- 

 cocci injected into a rabbit similarly prepared suffers very little 

 engulfing and extracellular development occurs rapidly. 



This difference in reaction of the leucocytes explains clearly the 

 difference in the evolution of the disease in the two animals. 



The exudate in a guinea-pig given a fatal dose is always richer in 

 leucocytes; the purulent peritonitis which usually occurs in an 

 infected guinea-pig is not found in an infected rabbit at autopsy. 

 When a guinea-pig dies as the result of an intraperitoneal injection 

 the exudate contains, in addition to a large number of leucocytes, 

 numerous streptococci. The blood of such an animal, however, con- 

 tains fewer organisms than does that of a rabbit under the same con- 

 ditions. It need scarcely be insisted upon that the more active the 

 phagocytic apparatus against a given bacterium, the more difficult 

 does the invasion of the blood by this organism become. The 

 extreme alterations in the blood (destruction of red blood cells) 

 found in the blood of rabbits and resulting from an abundant growth 

 of the streptococcus is not found in the guinea-pig at autopsy. 



Cases of streptococcus reinfection occurring after a period of 

 apparent cure, although rare in guinea-pigs, are, on the contrary, 

 very frequent in rabbits that have received a small dose of pro- 

 tective serum. What is the cause of this difference? 



Among the leucocytes that take up bacteria there are always a 

 certain number that die after having destroyed the parasites that 

 they contain; and so it is easy to understand how such bacteria, 

 which may be almost intact, are liberated. These liberated bacteria 

 are much more likely to be taken up again in a guinea-pig than in a 

 rabbit, since the guinea-pig leucocytes are more actively phagocytic for 

 the streptococcus. It may be, too, that guinea-pig leucocytes have 

 a greater destructive power for the streptococcus than rabbit leu- 

 cocytes. This leads us to v a consideration of the alterations in 

 streptococci taken up by cells in the two animals we are studying. 

 In both of these animals the leucocytes cause destructive altera- 

 tions in at least some of the phagocyted bacteria. 



