60 ESSAYS ON BACTERIOLOGY. 



Naturally, as the result of these discoveries, the at- 

 tempt has been made to find a bactericidal agent in 

 the blood. Hankin has been a leader in this special 

 work. He believes that he has established, for cer- 

 tain animals at least, that the blood contains a sub- 

 stance of a proteid nature which belongs to the globu- 

 lins and has certain bactericidal properties. Follow- 

 ing this supposition, he was able to neutralize inocula- 

 tions of anthrax by injection of a solution of this glob- 

 ulin. The tendency of investigation is unmistakably 

 in at least the general direction of Hankin's view. 



These albuminoid substances have been called de- 

 fensive proteids, and investigation seems to indicate 

 that they may act in one of three ways : first, by kill- 

 ing the bacteria, that is, microbicidal; second, by at- 

 tenuating or weakening the bacteria; third, by neu- 

 tralizing or destroying the toxines. In justice to the 

 work of Metschnikoff it must be said that this blood 

 . serum theory does not necessarily disprove his phago- 

 cytosis theory, for it is still q;iite possible that self- 

 limitation or immunity, or both, may result from 

 these defensive proteids acting upon or through the 

 cells. 



Behring and Kitasato found that the serum of rab- 

 bits vaccinated against tetanus had the property of de- 

 stroying the toxin of tetanus in guinea pigs, so that 

 gtiinea pigs might be cured of tetanus by injection of 

 rabbit serum taken from vaccinated rabbits. The 

 same authors proved a similar fact in regard to diph- 



