122 



PRECIP1TINS 



A constant amount of precipitinogen is placed in each of a row 

 Technique of f test- tubes, and to these are added diminishing amounts of 

 the Precipi- the immune serum, 

 tin Reaction. A set quantity of serum and varying amounts of precipitinogen 



can also be employed. The result of the reaction depends to 

 a very large extent upon the quantitative relationship of these in- 

 gredients. // relatively too much precipitinogen exists, a precipitate will not 

 form. An already formed precipitate will dissolve on the addition 

 of more precipitinogen. 



The explanation of this peculiarity is unknown. Since colloidal sub- 

 stances, however, at times give similar reactions, many authorities have 

 classed the precipitins among them. 



The technique of a precipitation test is best seen in the following table: 



A parallel row of tubes with normal serum should be included. 

 If highly valent sera, such as are obtained by immunization with 

 bacterial extracts, are employed, precipitation may result soon after 

 mixing the two constituents. The precipitins are strongly specific, al- 

 though it may be said that just as in agglutination, there exists in precipita- 

 tion a certain degree of "group reactions." 



The precipitation test has no clinical diagnostic value. It 



Diagnostic demonstrates nothing more than the agglutination test, is 



Value of more difficult of execution and associated with greater sources 



Bacterial of error. Only occasionally is it of service to prove the 



Precipitation, presence of soluble bacterial substances within exudates or 



organ fluids. 



Porges and v. Eisler have employed the precipitation test as a means for the differ- 

 entiation of capsule-bacteria where the method of agglutination is associated with 

 certain difficulties. The precipitinogen was produced by filtration of four- weeks-old 



