R. L. KAHN 859 



the concentrated globulin solution forming the basis for further quantitative study. This 

 solution is diluted 1:5, 1:10, and i : 20 with saline, and 0.15 cc. of each is tested with o.oi cc. 

 of antigen suspension. The tests are completed in the usual manner and the results computed 

 as in the case of the quantitative serum procedure according to the formula S = 4D where S 

 is the potency of spinal fluid in terms of reacting units and D is the highest dilution of the 

 concentrated globulin solution giving a positive precipitation reaction. The original spinal 

 fluid may be used for the i : 10 globulin solution and the i : 2 dilution of the spinal fluid for 

 the 1 : 20 g'obulin solution. If a precipitate is obtained in the i : 20 dilution, the final reaction 

 is 20X4 = 80 reacting units. In most cases, however, spinal fluids are negative in this dilution. 



Clinical application: As a check on treatment in neurosyphilis. 



"Micro-procedures."^ — These are special procedures which employ minute amounts of 

 serum or spinal fluid, and are employed only when insufficient quantities are available for 

 regular test. In the case of serum, one-tenth of antigen suspension in relation to serum is 

 employed. Thus, if 0.05 cc. of serum is available, 0.005 cc. of suspension is employed. In the 

 same way, any measurable amount of serum and suspension may be used. In the case of 

 spinal fluid, the globulins are precipitated in an amount that is available and the "micro- 

 procedure" performed with the dissolved globulin solution, employing fifteen parts of this 

 solution to one of antigen suspension. AH "micro-results" are interpreted as positive or nega- 

 tive, depending on the presence or absence of a precipitate. 



Procedure with fluid from syphilitic lesion. — Chancre or other syphilitic fluids are em- 

 ployed with antigen suspension in the proportion of 10: i, as in the case of micro-procedures. 

 Thus, if 0.03 cc. of fluid is available, it is employed with 0.003 cc. of suspension. In the case 

 of chancre fluid, precipitation reactions have been obtained even after 1:3 dilution with 

 saline. The results are interpreted as positive or negative. 



Procedure applicable to rabbit syphilis. — The quantitative serum procedure employing the 

 1:1, 1:5, 1:10, and 1 : 20 serum dilutions has been found to be applicable to the serum re- 

 action in rabbit syphilis. The results are interpreted on the basis of quantitative units, as in 

 human syphilis. 



Special investigation of a serum. — It is occasionally desired to study a serum giving nega- 

 tive results with the usual Kahn methods, for traces of syphilitic reagin. It is known that the 

 sensitivity of the precipitation reaction can be increased by prolonging the heating period of 

 the serum to one hour, by decreasing the amount of antigen suspension in relation to serum, 

 such as the use of a 20: i proportion of serum to suspension, and by increasing the shaking 

 period to seven or ten minutes. By applying these steps to a given serum, it is possible, 

 occasionally, to detect a minute amount of reacting substance. Such findings, while of no 

 general diagnostic value, may throw light on the diagnosis of an obscure case. 



APPLICATION OF KAHN REACTION 



Studies by different workers on the application of the Kahn reaction to clinical 

 medicine have been limited thus far almost entirely to the employment of the routine 

 diagnostic test. Judging from the results obtained, the test is comparable in specificity 

 and sensitivity to a reliable Wassermann reaction, although some claim the Kahn to 

 be more sensitive in primary syphilis and in treated cases. ^ It is obvious, however, 



' Kline, B. S., and Young, A. M. {J. A.M. A., 86, 928. 1926) recently suggested a microscopic- 

 slide test with very small amounts of serum and antigen dilution. 



^ The reliability of the Kahn reaction is generally accepted (Redfield, Faupel, Giordano, Owen 

 and Cope, Lederer, Button, Duemling, Pineda, Houghton, Hunter and Cajigas, Stucky and Huntley, 

 Johnson, Literer, McLean, Maynard, Berry, Ey and Belong, Walker, Hull, etc.). The Michigan Be- 



