KAHN TEST 
181 
suspension. Thus, if 0.05 cc. of serum is available, it is employed with 
0.005 cc. of antiijen suspension. Report these as micro tests. 
Quantitative Procedure With Serum.— The quantitative test deter- 
mines the relative number of reacting substances in syphilitic serum, 
the results being expressed in terms of reacting (Kahn) units. It is 
applicable to sera giving strong reactions. 
Serum Dilutions. — Frepave a series of 8 serum dilutions with phy- 
siological salt solution, such that the ratio of the volume of diluted 
serum to the volume before dilution ranges from 1 (undiluted serum) 
to 60 (1 part serum + 59 parts saline). The following scheme is 
employed : 
+ 0.7 cc. normal saline 
+ 0.2 cc. normal saline 
+ 0.4 cc. normal saline 
+ 0.3 cc. normal saline 
+ 0.4 cc. normal saline 
+ 0.5 cc. normal saline 
ilutio 
1 
Dilution 
No. ratio. 
1 . . . . 1 
= undiluted ser 
2 
5 
= 0.2 cc. undih 
3 
. 10 
= 0.7 cc. of (2) 
4 
. 20 
= 0.2 cc. of (3) 
5 
. 30 
= 0.2 cc. of (3) 
6 
. 40 
= 0.1 cc. of (3) 
7 
. 50 
= 0.1 cc. of (3) 
8 
. 60 
•= 0.1 cc. of (3) 
Preformance of Test.— Frepare standard antigen suspension as for 
routine test and measure 0.01 cc. amounts into 8 standard test-tubes. 
Add 0.15 cc. amounts of the 8 serum dilutions, in order, beginning with 
the highest dilution (8), to the tubes containing antigen suspension. 
Shake the mixtures of serum and antigen suspension three minutes. 
Add 0.5 cc. salt solution to each tube and shake sufficiently to mix 
the ingredients. After the salt solution has been added, the results are 
read. Record a definite precipitate (+ + + + , + + + , or + + ( as 
positive and a weak or negative precipitate (+, ±, or — ) as negative. 
Typical Reactions with the Quantitative Serum Procedure. 
Dilution ratio 
of serum . 
1. 
5. 
10. 
20. 
30. 
40. 
50. 
60. 
Highest dilu- 
tion ratio of 
Serum potency 
in terms of 
Diluted 
serum, cc. . 
Antigen sus- 
pension, cc. 
0.15. 
0.01. 
0.15. 
0.01. 
0.15. 
0.01. 
0.15. 
0.01. 
0.15. 
0.01. 
0.15. 
0.01. 
0.15. 
0.01. 
0.15. 
0.01. 
serum giving 
definite pre- 
cipitin 
reaction. 
D. 
reacting units 
(equivalent to 
4D). 
S. 
1 . . . 
Pos.i 
1 
4 
2 
Pes. 
Pos. 
5 
20 
3 
Pes. 
Pos. 
Pos. 
10 
40 
4 
Pos. 
Pos. 
Pos. 
Pos. 
20 
80 
5 
Pos. 
Pos. 
Pos. 
Pos. 
Pos. 
30 
120 
6 
Pos. 
Pos. 
Pos. 
Pos. 
Pos. 
Pes. 
40 
160 
7 
Pos. 
Pos. 
Pos. 
Pos. 
Pos. 
Pos. 
Pos. 
50 
200 
Determination of Reacting (Kahn) Un.its.—li a serum gives a posi- 
tive reaction only before dilution it is considered as containing 4 units. 
1 Pos. = definite precipitation reaction (-(- + -h + , -f-fH-or -|--|-). 
