14 



coccus infections in man the tissues are invaded by virulent streptococci 

 but in a majority of these cases the cocci disappear sooner or later and the 

 patients make a complete recovery. Freshly drawn human serum has no 

 streptococcidal powers in vitro and it is reasonable to suppose that it has 

 none in the body during life. We must look therefore for some other 

 agent than the serum alone to account for the disappearance of the cocci 

 from the tissues during convalescence. According to Metchnikoff and 

 his followers this agent is found in the phagocytes and this view seems to 

 explain the facts better than any other theory that has been advanced. 



I next undertook a series of experiments to determine more accu- 

 rately what factors are concerned in the destruction of the invading 

 cocci in cases of human streptococcus infections, and to analyze more 

 fully this phenomenon. In all instances where blood was used it was 

 drawn from the vein at the elbow by means of a Luer syringe and de- 

 fibrinated by gently whipping with a sterile wire. If the defibrinating 

 is carefully performed not a very large proportion of the leucocytes are 

 destroyed. In the experiments each tube contained from 0.8 to i.o c. c. 

 of blood or serum which was inoculated with one loopful of streptococcus 

 culture and two loopfuls from each tube were plated in glucose agar at 

 intervals. The tubes were always kept in the incubator at 36 C. When 

 highly virulent organisms were used 0.3 to 0.4 c. c. of defibrinated rabbit 



TABLE 6. 



THE EFFECT OF DEF1B1IINATED NORMAL HUMAN HLOOD AND HUMAN SERUM ON STREP- 

 TOCOCCI. 



Strepto- 

 cocci. 



300 



300 



300 



300 



300 



300 



300 



298 



298 



298 

 B104 

 B104 

 B104 

 B104 



381 



300 



298 



Defibrinated 

 Blood. 

 I 



II 



I la 



III 



IV 



V 



VI 



VII 



VII 



VIII 



I la 



III 



IV 



V 



VI 



Serum IV 

 Semin VII 



5 hours. 



160 



1060 



1300 



3500 



2600 



240 



390 



315 



315 



16 



510 



Many 



Many 



900 



Many 



Many 



10000 



