MECHANISM OF ANTIBODY FORMATION 91 



'provokes a more active production of antibody. This is seen 

 more clearly with toxoids than with particulate antigens, but 

 when looked for can be observed with all types of antigens. 

 The latent period is shortened, the antibody titer rises more 

 rapidly and to a higher titer, and the rate of subsequent fall is 

 slower, 



(3) "Antibody in the circulation is being constantly removed at a 

 rate which is approximately proportional to its concentration. 

 This is based largely on the data from passive immunity ex- 

 periments with sera of the same species, but adequate reasons 

 have been given for assuming that it holds also for actively 

 produced antibody. 



(4) "Antibody production following an antigenic stim,ulus rises 

 to a peak and then diminishes, but continues at a dim,inishing 

 rate often for long periods. The classical example is the 

 persistence of demonstrable yellow fever antibody more than 

 fifty years after the last contact with the virus. 



(5) 'Antibody production can continue long after the antigen 

 responsible has disappeared from, the body. This conclusion 

 is perhaps debatable, but reasons have been given earlier for 

 adopting it. The alternative, to suppose that the cell retains 

 the antigen unmodified but undetectable by any experi- 

 mental method, is against all biological analogies, creates 

 grave difficulties in interpreting qualitative changes in anti- 

 body with repeated immunization, and could only be adopted 

 if no other interpretation could account for the facts. 



(6) 'Antibody production is a function not only of the cell 

 originally stimulated, but of its descendants. The cells of 

 the reticulo-endothelial system are well known to vary enor- 

 mously in number and in response to physiological and 

 pathological stimuli. The inoculation of antigenic and non- 

 antigenic foreign material is one of the most potent methods 

 of inducing their proliferation. Although direct proof is im- 

 possible, it is a reasonable assumption from this lability in 

 numbers that the life of any of these cells is a short one, and 

 that when antibody production goes on for months or years 

 other cells than those initially stimulated must be respon- 

 sible." Rejecting the persistence of thorium dioxide in the 



