KAHN TEST 183 
Shaking and Addition of Salt Sohdion.—Aiter mixing the concen- 
trated fluid with antigen suspension, shake the tube vigorously for three 
minutes. Add 0.5 cc. normal saline to tube. A definite precipitate 
suspended in a clear medium is read 4+. Proportionally weaker 
precipitates are read 3, 2 and 1 +, respectively. (The spinal fluid 
procedure may be carried out with 1.5 cc. spinal fluid + 1 cc. saturated 
ammonium sulphate solution. Dissolve the globulin precipitate in 
0.15 cc. normal saline (instead of 0.3 cc.) and perform the test with 
0.01 cc. of antigen susj)ension). 
Quantitative Spinal Fluid Procedure. — If the qualitative spinal-fluid 
test is positive, the remaining 0.15 cc. of concentrated globulin solution 
may be utilized for performing the quantitative test. 
Preparation of Glohnlin {or Spinal Fluid) Dihdions.—A series of 
four dilutions of the concentrated globulin solution with normal saline 
are prepared so that the ratio of the volume after dilution to the volume 
of the globulin solution before dilution ranges from 5 (1 part globulin 
solution -{- 4 parts of saline) to 20 (1 part globulin solution + 19 parts 
of saline) according to the following scheme: 
Concentrated globulin solution used in qualitative procedure 
0.15 cc. concentrated globulin solution + 0.6 cc. normal saline 
0.4 cc. of (2) concentrated globulin solution + 0.4 cc. normal saline 
0.2 cc. of (3) concentrated globulin solution +0.1 cc. normal saline 
0.2 cc. of (3) concentrated globulin solution + 0.2 cc. normal saline 
If 0.6 CC. of the original spinal fluid is available, dilutions for the 
quantitative procedure should be prepared by the following simpler 
alternative method •} 
0.15 cc. concentrated globulin solution + 0.6 cc. normal saline 
original (unconcentrated) spinal fluid 
0.2 cc. of (3) +0.1 cc. normal saline 
0.2 cc. of (3) + 0.2 cc. normal saline 
Performance of Te^/.— Prepare standard antigen suspension using the 
same titer as for routine tests with serum. Measure 0.01 cc. amounts 
of the suspension to the bottom of 4 test-tubes. To the tubes contain- 
ing antigen suspension, measure 0.15 cc. amounts of the dilutions, in 
order, beginning with the highest dilution ratio. Shake tubes vig- 
orously for three minutes. Add 0.5 cc. salt solution to each tube and 
shake gently to insure thorough mixing of the ingredients. After 
adding the saline, the results are read. Record a definite precipitate 
(+ + + + , + + + or + + ) as positive, and a weak or negative pre- 
cipitate (+, =•= or — ) as negative. 
volume of diluted globulin solution 
' Dilution ratio is here defined as — . The dilu- 
volume of undiluted globulin solution 
tion ratio, which is 1 for the concentrated globulin solution itself, is approximately 20 for 
a dilution of the spinal fluid itself made up of 1 part of fluid + 1 part of saline. 
Dilution 
Dilution 
No. 
ratio. 
1 . 
1 
2 . 
5 
3 
10 
4 . 
15 
5 . 
20 
Dilution 
Dilution 
No. 
ratio. 
2 . 
. 5 
3 . 
. 10 
4 . 
. 15 
5 
. 20 
