MODIFIED AND CONJUGATED ANTIGENS 345 



(1) "When iodine is added to animal sera (antigen) without 

 the presence of acid or alkali, substances are formed which pre- 

 cipitate witli antisera i)re])arcd from iodinated sera. 



(2) "This takes place in the presence of aqueous solutions as 

 dilute as N/32. 



(3) "Wormall's observation that diiodotyrosinc, but not potas- 

 sium iodide, inhibits precipitation specifically in sj^stems of 

 iodinated proteins and their antisera was confirmed." 



Minimum Amount of Iodine to Change Antigenic Property. — 

 To ascertain the minimum amount of iodine necessary to alter a 

 protein antigenically, lie added 2.0 c.c. of iodine solutions corre- 

 sponding to iodine concentrations of N/8, N/16, N/32, and N/64 

 to 1.0 c.c. of normal horse serum and the mixtures were allowed 

 to stand at room temperature for fifteen minutes. Jacobs says 

 that "a minimum amount of acetic acid was added and the pre- 

 cipitates were centrifuged, taken up in 10 c.c. of saline with the 

 aid of just enough dilute carlionate to adjust the pH to approxi- 

 mately 7.5, and filtered through a Berkefeld V candle until clear." 

 In the tests he used dilutions of this solution corresponding to 

 1:10, 1:50 and 1:250. "The supernatants were precipitated with 

 three-fourths saturated ammonium sulphate, taken up in 10 c.c. of 

 saline, pH adjusted to 7.5 and passed through a Berkefeld filter. 

 Dilutions were made up comparable to those of the first precipi- 

 tate. Both precipitates and supernatants M^ere examined im- 

 munologically for the presence of normal horse serum and iodi- 

 nated precii>itinogen." He found that it required at least N/32 

 iodine to alter the antigen immunologically. In these altered 

 antigens there remained unaltered horse serum. He observed a 

 diminution of unaltered antigen as more iodine was added until 

 only a trace was left in the preparations containing the maxi- 

 muni amount of iodine. 



Specificity for Iodized Proteins. — Like Obermayer and Pick 

 (1906), Wormall (1932), Landsteiner and others, he found that 

 the immune serum for iodized liorse serum reacted with other 

 iodized antigens. 



Group Reactions Due to Different Haptens in the Same Mole- 

 cule. — Hooker and Boyd (1933) have coupled diazotized arsanilic 

 acid to egg white and gelatin, respectively, and found them both 

 to be antigenic despite the fact that gelatin is not antigenic. The 



