584 BACTERIOLOGY. 



ondary process, the bacteria being taken up by the leu- 

 cocytes only after having been modified through the 

 opsonizing activity of the serum of the blood and of other 

 fluids in the body. 



9. That of the hypotheses advanced in explanation 

 of acquired immunity, the one worthy of greatest con- 

 fidence is that which assumes immunity to be due to 

 reactive changes on the part of the tissues that result 

 in the formation in these tissues of antitoxic and other 

 anti-bodies, which circulate free in the blood, and in a 

 variety of ways serve to protect the tissues from the 

 harmful effect of extraneous intoxicants and irritants, 

 in some cases acting principally as antidotes to a toxin, 

 in others exhibiting more the germicidal (bacteriolytic) 

 than the antitoxic property. 



