PRECIPITIN TESTS IN SYPHILIS 

 Tabf.e XIV 



455 



- = No flocculation. 



-f = A'ery slight flocculation. 



+ 4 = Slight flocculation. 



+ + + = Moderate flocculation. 



4 -n- -I- = Complete flocculation. 



.syphilitic serum and no tendency to produce nonspecific pre- 

 cipitate. 



Time of Reading Results. — The results are read immediately 

 after the addition of salt solution and a second reading is made 15 

 minutes later. The six tube readings thus obtained are added and 

 divided by 6, plus minus (±) readings being disregarded. He 

 reports all readings of % or less as negative, % and % as doubt- 

 ful and readings more than % as positive. For further details see 

 Supplement No. 11, U. S. P. H. Service. 



Controls. — The test includes a positive serum, a negative serum, 

 an antigen and a patient's serum control. Positive controls must 

 have a precipitate while negative controls are free from a pre- 

 cipitate. The serum control is necessary to show that the serum 

 under test will not give a pscudoprecipitate Avith saline solution 

 only. The antigen control rules out any spontaneous precipita- 

 tion of antigen by saline solution. To avoid false reactions, a 

 weak + + + + or a + + + serum should be used as a positive control. 

 This practice permits the discovery of slight mishaps in technique 

 that would otherwise be unrecognized. 



Choice of Kahn Test. — Three separate tests, besides his new 

 verification test, are described by Kahn (1940). The routine test 

 is employed in the general diagnosis of syphilis and as a routine 

 test on admittance of cases to hospitals, etc. This is a three- 



