128 



Scientific Proceedings (119). 



and the remaining rats, which were the progeny of splenectomized 

 parents, were observed for 23 weeks. In no case was there evi- 

 dence of an increased appetite nor of variation from the normal 

 growth rate. 



Erythrocyte count on five of the "second generation" splenec- 

 tomized rats gave no indication of anemia following the operation. 



63 (1810) 



Determination of optimum amount of antigen in complement 



fixation tests. 



By R. L. KAHN and S. R. JOHNSON. 



[From Bureau of Laboratories, Michigan Department of Health, 



Lansing, Mich.] 



A study of the quantitative relation between antigen and 

 antibody in complement fixation, suggested a simple procedure 

 for determining the optimum amount of antigen in these tests. 

 Wassermann, protein and bacterial antigens were employed with 

 their specific antisera. It was observed in the case of the Wasser- 

 mann antigens (alcoholic, cholesterinized and Noguchi), that each 

 one appears to possess an optimum concentration for binding 

 complement with positive sera. This concentration could be 

 determined only with weak positive sera, preferably those giving 

 + and ++ reactions. The stronger positive sera do not seem 

 to be markedly affected by the quantity of antigen employed. 



The procedure consists in first determining the antigenic unit, 

 or smallest quantity which gives complete fixation with some 

 positive serum. A weekly positive serum is then pipetted into a 

 series of 10 tubes, employing the same quantity used in the regular 

 tests. The first tube then gets \ unit antigen; the second, \ 

 unit; the third, I unit, etc.; the last tube getting about 10 units of 

 this ingredient. After the fixation period, it will be observed, on 

 adding sensitized cells, that certain tubes — not necessarily those 

 containing the largest amount of antigen — will show the maximum 

 amount of fixation. The number of antigenic units contained in 

 these tubes being known, therefore, that number showing the 

 maximum fixation, represents the optimum amount of antigen to 



