A STUDY OP FIXATION REACTIONS. 369 



ployed in order to obtain a racial differentiation, and thereafter a second deflec- 

 tion test be performed with weak immune serum for more delicate differentiation 

 between the various body tissues or secretions. 



INTERPRETATION OF RESULTS. 



Clear cut results with satisfactory controls are received as conclusive 

 by almost all observers. However, a large measure of confusion lias been 

 caused by the fact that some one or more controls are often omitted or 

 because the resulting deflection is not as absolute as could be desired. 

 When Wassermann first put forward this method he advanced the opinion 

 that a positive result could be obtained only in the event of antibody and 

 antigen uniting. The greater amount of work of this nature has been 

 done in the investigation of suspected syphilitic serum, and up to the 

 present time but few cases have been reported in which a positive result 

 was obtained from a patient unquestionably free from infection. These 

 few exceptions will be discussed later together with the change in the 

 interpretation of the reaction which has been brought about by the rapid 

 accumulation of fresh data. It may be stated that practically all 

 investigators agree that the serum diagnosis proves more quickly and 

 more certainly than any other method whether syphilis is or has been 

 present, However, there are a number of other causes which produce 

 deflection of a non-specific character. Bruck( 15 ) reports that serum 

 can be modified in its action by heat. Treatment at 55 degrees for half 

 an hour usually reduces the power so that it is rare to obtain deflection 

 with less than 0.3 cubic centimeter of such a serum. Normal monkey 

 serum when heated for half an hour to 60 degrees acquires strong powers 

 of deflection so that 0.1 will bind four times the dissolving dose . of 

 complement twice in succession, or in a single quantitative experiment 

 will bind ten times the dissolving dose. Brack compares this with the 

 Pfeiffer-Friedberger reaction within the normal body. He finds that 

 monkey serum is affected by heat in this manner with great regularity, 

 guinea-pig serum less frequently, and rabbit serum still less. If the 

 temperature is raised to G5° within 15 minutes the deflecting power is 

 completely destroyed. He thinks it probable that the changes in deflec- 

 tion are due to molecular changes comparable to those occurring on long 

 standing. 



In the serum diagnosis of syphilis it has been frequently observed 

 that a specific luetic serum will react with extracts of normal organs, 

 particularly if a large amount of extract is employed. Even in this 

 case, however, it is always necessary to employ a luetic serum in the 

 test. Wassermann ( 19 ) was at first inclined to believe that this was a 

 peculiarity of old extracts, but this does not seem to be the case. 



A positive deflection may sometimes be observed in the control with an extract 

 of liver itself, and Michaelis(4) also found that normal, non-deflecting serums 

 may become deflecting after being kept frozen for a long time. 



