658 



SCIENCE 



[N. S. Vol. XXVII. No. 695 



freely susceptible to phagocytosis, as is the 

 ease when grown in broth or upon agar, 

 have become fairly resistant instead. 

 When grown in normal serum they fail 

 to acquire this resistance to the action of 

 opsonin and the leucocyte. 



Extracts from highly virulent pneu- 

 mococci contain a substance or combination 

 of substances which neutralize the opsonin 

 in serum. This substance unites with viru- 

 lent pneumococci quantitatively and by so 

 doing confers upon them a degree of resist- 

 ance to phagocytosis as well as to animal 

 virulence. The extracted virulent pneu- 

 mococci now acquire the power to absorb 

 pneumocoeco-opsonin. In other words, it 

 seems possible to extract from virulent 

 pneumococci the substance upon which 

 virulence probably depends and to which 

 the name ' ' virulin ' ' has been given. While 

 the action of virulin may be the subject of 

 several hypothetical explanations, at pres- 

 ent it is probably best to look upon it 

 simply as a substance or mixture of sub- 

 stances which when united with the pneu- 

 mococcal cell prevent the cell from taking 

 up opsonin, and which substance, when 

 free, has special affinity for opsonin. That 

 it does not merely concern free opsinophile 

 cell receptors seems likely because virulent 

 pneumococci when extracted, that is, freed 

 from virulence, are found to absorb pneu- 

 mocoeco-opsonin freely. 



The Mechanism of Streptococcus Im- 

 mmlity: Gustav F. Ruedigek. 

 In a previous paper it was shown that, 

 in test-tube experiments, suspensions of 

 rabbit leucocytes in normal rabbit serum or 

 blood destroy avirulent streptococci but not 

 the virulent organisms. Suspensions of 

 the leucocytes in heated serum or in 0.85- 

 per-cent. NaCl solution do not destroy the 

 avirulent streptococci. Dr. Hektoen and I 

 have shown that the avirulent streptococci 

 are freely taken up by rabbit leucocytes 



in normal serum, but the virulent organ- 

 isms are not taken up. Washed rabbit 

 leucocytes in heated serum or in 0.85-per- 

 eent. NaCl solution do not ingest the aviru- 

 lent streptococci. 



Rabbits were now immunized according 

 to Neuf eld 's method by injecting them first 

 with a large dose of heated virulent strep- 

 tococci and then with several doses of the 

 living culture. These animals acquired an 

 immunity so that they did not succumb 

 to a subcutaneous injection of twice the 

 minimum fatal dose of the streptococcus. 

 In test-tube experiments it was now found 

 that normal rabbit leucocytes, or washed 

 leucocytes from an immune rabbit, when 

 suspended in the immune rabbit serum, 

 freely ingest the virulent streptococci. If, 

 however, these leucocytes are suspended in 

 normal rabbit serum they scarcely take up 

 any of these streptococci. No difference 

 could be detected between the normal 

 leucocytes and those coming from an im- 

 mune rabbit. The immunity is dependent 

 upon a change in the serum, as' the follow- 

 ing experiment shows. Virulent strepto- 

 cocci were sensitized in the immune rabbit 

 serum and another lot was treated simi- 

 larly with normal serum. These cocci were 

 suspended separately in salt solution and 

 each suspension was added to a suspension 

 of washed rabbit leucocytes in salt solu- 

 tion. It was found that the streptococci 

 which had been sensitized in the immune 

 serum were taken up by the leucocytes to 

 the extent of eight per leucocyte, whereas 

 those which had been sensitized in the 

 normal serum were not taken up at all. 

 That is, the serum had acquired something 

 by virtue of which it was enabled to sensi- 

 tize the virulent streptococci so that they 

 were ingested by the rabbit leucocytes. 



The immune rabbit serum does not 

 possess anti-streptolytie properties. 



Fourth Meeting. — Papers in joint session 



