PRECIPITIN TESTS IN SYPHILIS 449 



i>eii and synergistic substances. It also affects the potential dif- 

 ferences indirectly through its effect on the dissociation of elec- 

 trolytes. Moreover, the reagin-filmed particles change from a 

 liophylic to a liophobic surface interface resulting in precipitation. 

 The water apparently has a physical role. 



Electrolytes. — The function of electrolytes in the precipitation 

 test is identical with their action in the agglutination reaction. 

 The reagin-lipoid complex acts as a denatured protein. This re- 

 sults in a lowered P.D. between the particles with drastic reduc- 

 tion in their repulsive forces. When such particles come in contact 

 through agitation or other physical means, sticky aggregates are 

 held together by the cohesive force. 



From this it is evident that the concentration of electrolytes 

 has an important bearing on the sensitivity of the test. Precipita- 

 tion occurs with greater ease as the concentration of the elec- 

 Irolytes is increased. It also becomes more sensitive as the valence 

 of the metallic ion is increased. 



The various electrolyte concentrations which have been used 

 in precipitation tests are listed in the following table : 



Kahn 0.90 per cent sodium chloride 



Kline 0.85 per cent sodium chloride 



Meinicke 3.00 per cent sodium chloride and 



0.01 per cent sodium carbonate 

 Hinton 5.00 per cent sodium chloride and 



0.022 per cent salicylic acid 

 Rosenthal 0.40 per cent (only serum electrolytes) 



Citochol 0.85 to 3.00 per cent sodium chloride 



Mazzini 1.00 per cent salt concentration 



(buffered saline) 



Deissler and Baker (lOSf)) and others favor the increase in the 

 electrolyte concentration as a means of increasing sensitivity and 

 velocity of the reaction. From two to three per cent sodium 

 chloride has given more satisfactory citochol reactions in the 

 laboratories of the above workers and in many other laboratories. 



Alcohol. — The lipoids are usually dissolved in alcohol or some 

 similar lipoid solvent. The alcohol has no role in the precipitation 

 of the particles. It serves as a solvent for the lipoids until disper- 

 sion is accomplished from the solution by diluting it with water. 

 It is an inert ingredient in the finished antigen since the changes 

 in ionization constants are negligible. 



