no 



PRECIPITINS. 



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 carrying out 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, although it may be said 

 that just as in agglutination, there exists in precipitation 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 o f error. Only occasionally is it of service to prove the 



Precipitation. p resence o f soluble bacterial substances within exudates or 



organ fluids. 



Forges and v. Eisler have employed the precipitation test as a means for the differen- 

 tiation of capsule-bacteria where the method of agglutination is associated with certain 

 difficulties. The precipitinogen was produced by nitration of four-weeks-old bouillon 

 cultures of pneumococci, rhinoscleroma, and ozoena bacilli. The immune serum was 

 obtained from rabbits which had received four to five subcutaneous injections of the 

 bacterial suspensions. 



Fornet has recently advocated the precipitation test as an aid in the 

 clinical diagnosis of typhoid. Although his attempts have not been attended 

 with practical success, the principles of the reaction deserve discussion on 

 account of their originality. 



Fornet believed that it should be possible to demonstrate in the blood of typhoid 

 patients the presence of the antigens (precipitinogens) which stimulate the antibodies, long 

 before the latter themselves become evident. He actuallv was able to obtain turbid 



