852 THE KAHN REACTION 



The first step in standardizing a newly made antigen is to determine the minimum 

 amount of normal saline to add to i cc. of antigen producing lipoid particles that 

 will readily disperse in additional saline. This is spoken of as the "titre" of the 

 antigen, and when determined the second step is to examine a number of negative, 

 positive, and especially weakly positive syphilitic sera with the antigen using this 

 titre, and with standard antigen as a control. If the sensitivity of the new antigen is 

 similar to that of the standard, the new antigen is classed as "standard." If not 

 similar, one of the several methods of antigen correction is employed, depending on 

 the nature of the antigen. 



I. An antigen might be more sensitive than the standard — due, probably, to a 

 greater concentration of specific lipoids. Since both excessive dilution and excessive 

 concentration of lipoids reduces antigen sensitivity, the oversensitive antigen may be 

 reduced in sensitivity either by still further increasing its lipoid content by concentra- 

 tion or by decreasing its lipoid content by dilution. 



One of two methods of antigen dilution may be used: (i) The antigen may be 

 diluted with alcohol (cholesterolized antigen with cholesterolized alcohol). Ten and 

 20 per cent dilutions may be tried. Each diluted product is compared in sensitivity 

 with standard antigen. If not comparable, greater or lesser dilution is resorted to. 

 (2) The saline in the antigen suspension may be increased beyond the minimum 

 amount. Thus, if the titre of a given antigen is i cc. of antigen plus i.i cc. of saline, 

 1.2 and 1.3 cc. of saline may be tried and each antigen suspension compared in sen- 

 sitivity with standard antigen. 



When reducing antigen sensitivity by increasing the lipoid concentration the fol- 

 lowing procedure is employed: A given amount, such as i cc. of non-cholesterolized 

 antigen is evaporated to dryness. The residue is dissolved in 10 cc. of cholesterolized 

 antigen and the sensitivity of the final product tested against the standard. If not 

 comparable, an antigen of a different degree of concentration is prepared and tested. 



II. An antigen might be less sensitive than the standard — due either to excessive 

 or to insufficient concentration of lipoids. If it is due to excessive concentration, the 

 method of alcohol dilution, or that of increasing saline in the titre, just discussed, 

 will increase the sensitivity of the antigen. If, on the other hand, insufficient con- 

 centration is the cause of lesser sensitivity, either one of two methods may be 

 employed: (i) the concentration of alcoholic extractives, already presented, or (2) 

 the addition of ether extractives to the antigen. This is carried out as follows: 

 The accumulated ether extract from the antigen preparation from 25 gm. of beef 

 heart is evaporated to about 50 cc. and cleared by filtration. A small amount of 

 this extract (0.5-1 per cent) is added to the antigen and the final product compared 

 in sensitivity with the standard antigen. If not comparable, a different amount of 

 the ether extract is added to the antigen and the product tested against the standard. 



For several years past practically all antigens in the writer's laboratory requiring 

 correction have been brought up to standard requirements by alcohol dilution. The 

 preliminary antigen titration and subsequent tests with serum in comparison with 

 standard antigen furnished the clue as to the extent of alcohol dilution to employ. 

 Of two antigens requiring concentration, one was corrected by the addition of ether 

 extractives, and the other by the addition of alcohol extractives, apparently with 



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