546 INFECTION AND IMMUNITY. 



may be found within the leucocytes in both natural 



and experimental infections. When injected into 



the pleural or peritoneal cavity of the guinea-pig 



phagocytosis is well begun within one-half hour 



and reaches its height in four to five hours. 



Bactericidal Experiments which were begun by van der Velde 



C cocytes iSd in 1894 demonstrate the bactericidal action of leu- 



cocytic exudates. The action is not so strong in 

 the cell-free exudate as when the leucocytes are 

 present, and when the leucocytes are caused to dis- 

 integrate by some means, as by alternate freezing 

 and thawing, trituration, the action of leucocidin, 

 or treatment with distilled water, the bactericidal 

 power of the fluid is increased. Presumably the 

 leucocytes discharge their bactericidal contents into 

 the surrounding fluid as a result of such inju- 

 ries. The nature of the bactericidal substance is 

 not known exactly; from the fact, however, that 

 leucocytes contain complement it has been suggest- 

 ed that they discharge this complement which then 

 acts with amboceptors in the serum in destroying 

 the organisms. It is possible that the cocci before 

 they are taken up by the leucocytes have absorbed 

 amboceptors and after their ingestion are suscepti- 

 ble to the action of the endocellular complement. 

 In contrast to the distinct bactericidal power of the 

 leucocytes stands the very low or entire absence of 

 a similar action by both normal and immune 

 serums. It would seem, then, that the most power- 

 ful agency in natural resistance to invasion by the 

 staphylococcus is represented in the phagocytic 

 and bactericidal activities of the leucocytes. Opso- 

 nins are essential for phagocytosis. 



Active-im- In 1888, Eichet and Hericourt showed that it 

 pogsible to increase t he resistance of the rabbit 



