26 



tube were now added .2 c. c. suspension of washed rabbit corpuscles 

 containing leucocytes from a pleural exudate and .2 c. c. suspension of 

 streptococci of medium virulence. Two additional tubes with unheatecl 

 normal and immune serum were prepared in the same manner and all 

 tubes incubated ]/ 2 hour. Smears were now made from all tubes and 

 stained and the degree of phagocytosis in each tube determined by count- 

 ing the cocci in each of 50 leucocytes, with the following result : 



Phagocytosis. 



Heated normal serum ~j- washed corpuscles + streptococci . ! 1.1 



Heated immune serum + washed corpuscles + streptococci 4.5 



Normal serum -f washed corpuscles + streptococci 4.3 



Immune serum + washed corpuscles -f- streptococci 7.3 



Washed corpuscles in NaCl solution + streptococci 1.1 



The experiment shows that the opsonin of the immune serum is only 

 slightly disturbed by heating at 60 C. for y 2 hour, whereas that of nor- 

 mal serum is entirely destroyed at that temperature. 



CONCLUSIONS. 



The normal sera of man, rabbits and guinea-pigs have no strep- 

 tococcidal power and do not acquire such a property in the course of a 

 streptococcus infection. 



Suspensions of organ cells of guinea-pigs have no streptococcidal 

 powers. 



Defibrinated human blood is distinctly streptococcidal and this prop- 

 erty is roughly proportional to the number of leucocytes the blood con- 

 tains per cubic millimeter. 



Normal leucocytes of rabbit, guinea-pig and man, suspended in 

 normal serum or blood, freely ingest non-virulent streptococci and de- 

 stroy them. The washed leucocytes in NaCl solution or in heated serum 

 do not ingest these organisms, but the latter multiply in these suspen- 

 sions. If, however, the streptococci are treated with normal serum, 

 washed and then added to a suspension of washed leucocytes they are 

 ingested and destroyed by the leucocytes. In the phagocytosis of strepto- 

 cocci, therefore, it is essential that the organisms should first be sensi- 

 tized, that is, acted upon by the opsonin of the serum. 



The leucocytes of guinea-pigs and of man take up living strepto- 

 cocci in vivo, and in all probability destroy them. It seems evident, 

 therefore, that the phagocytes, acting in conjunction with the opsonin of 

 the serum, are the most important (if not the only) factors concerned 



