66 IMMUNO-CATALYSIS 



chicken which had produced antihorse serum precipitating with 

 1 : 102,400 dilution of antigen, showed no precipitin when bled five 

 hours after the reinjection of homologous horse serum antigen, but 

 the titer had risen to 409,600 when bled six days after the reinjection 

 of antigen. The other chickens showed similar behavior in every 

 respect. 



Using quantitative chemical technique and horse serum and crystal- 

 line egg albumin as antigens, Culbertson (1935) in a similar study 

 made the following observations : 



After its injection into the circulation the horse serum as antigen 

 persisted much longer in the blood of normal rabbits than of immune 

 rabbits. In the normal animals, injected for the first time, complete 

 removal of the antigen was never effected before the appearance of the 

 precipitins in the blood. 



All of the crystalline egg albumin introduced combines with circulat- 

 ing precipitin, which is immediately available for union with foreign 

 protein. When the antigen is given in slight excess, a small residue of 

 circulating precipitin generally remains in the blood. When large excess 

 of antigen is given, antigen persists free in the circulation for about as 

 long as an injection of similar size persists in the blood of a normal 

 animal. The fixed tissue antibody is available in much less amount, 

 and functions only when some of the antigen escapes union with the 

 circulating precipitin and reaches the fixed tissues. 



The above relationship between the circulating precipitin and 

 homologous antigen is not altered by the injection of numerous non- 

 specific substances into the circulation. 



Hektoen and Welker (1935) also observed that the reduction or 

 complete disappearance of antibody from the blood after introduction 

 of the specific antigen, is sharply specific and that in the rabbit im- 

 munized against many antigens the injection of one of the antigens as 

 the rule resulted in the disappearance from the blood of the precipitin 

 for that antigen only. Lewis (1912) reported that diphtheria horse 

 antitoxin, if injected into rabbits which had been previously injected 

 with horse serum, was considerably less effective in neutralizing diph- 

 theria toxin subsequently injected than in normal rabbits. Romer and 

 Viereck (1914) reported that, in guinea pigs sensitized against horse 

 serum, antitoxin injected into the blood disappeared more quickly than 

 it did in normal animals. According to Hooker and Follensby (1931) 



