PRECIPITIN TESTS IN SYPHILIS 445 



the i'orniation of an ultramieroscopic precipitate. While the eoni- 

 })lieated procedure involved in the Jacobstahl method was im- 

 practical, it stimulated extensive research in this field. Bruck 

 and Hidaka (1911) modified this method so that the precipitate 

 was microscopic rather than ultramieroscopic in character. Mein- 

 icke (1917, 1918, 1920) followed with several modifications. In 

 the same period Sachs and Oeorgi (1920) suggested cholesterol as 

 an added substance to increase the sensitivity of the tissue extracts. 

 Although the Sachs-Georgi reaction has been generally discarded, 

 their principle of adding cholesterol or a similar sensitizer to rein- 

 force the tissue extract has made the practical development of the 

 flocculation test possible. I\Iany tests have been and are being pro- 

 posed with the objective of increasing specificity or sensitivity 

 or botli, but thus far they are modifications of this original method. 



Simplicity of Flocculation Method. — The simplicity of the floc- 

 culation methods contrasts sharply with many of the proposed com- 

 plement fixation procedures. The methods combine high sensitivity 

 and specificity, rapid results and stable standardized reagents at a 

 low cost per test. It further permits the use of several methods as 

 a check on each other with economy of time. 



Status of Flocculation Tests. — The value of the precipitation 

 nu'thod for tlie detection of sypliilitic reagin is still a contro- 

 versial subject. However, the widespread acceptance of such 

 tests as the Kahn, Meinicke, Kline and others is an expression 

 of approval by most syphilologists. From the present state of 

 confusion generally standardized precipitation methods will de- 

 velop which have adequate confirmation and of a specificity and 

 sensitivity consistent with clinical practice. While many of the 

 modifications are commendable, the process of standardizing has 

 ]u-ogressed slowly, due to the many technical modifications in use. 

 It is difficult to pick an ideal test witli such an assortment from 

 which to choose when each offers one or more characteristic ad- 

 vantages. 



Principle of Flocculation Tests. — The basic mechanism of all 

 precipitation tests is essentially the same. They differ in points 

 of technique, sensitivity, and interpretation. A positive reaction is 

 characterized hy the formation of aggregates which result from 

 the combination of the lipoid suspension and "reagin" found in 

 syphilitic serum but not present in nonsyphilitic serum. The 



