374 Mr. A. H. Caulfeild. Inhibitive and Fixation [Aug. 24, 



anti-complementary result to one which may be termed antigenic with the 

 original restrictions of that term. Since my earlier observations on the 

 inhibitive reaction and the reaction of fixation, a number of factors have 

 appeared that have necessitated changes in the technique, in order to obtain 

 more correct interpretations of the end results. While these factors have 

 been mentioned to some extent in the literature upon complement-fixation 

 tests, the importance of their influence has not been brought out. 



The technique of the inhibitive reaction has been developed with an 

 alcohol-ether extract of the tubercle bacillus, finally prepared as a 2-per-cent. 

 stock solution. Four dilutions of this stock solution are used, the first of 

 which is fully anti-complementary with saline, a 1/10 to 1/20 further 

 dilution gives the antigenic strength, while the intermediate dilutions of 

 1/2 and 1/4 dilutions represent more or less anti-complementary strengths. 

 With these four dilutions, three main types of end results with pathologic 

 sera become evident. 



1. Inhibitive Reaction. — With these sera, according to their activity, 

 partial to complete hsemolysis results with the full anti-complementary 

 strength of antigen. Because of certain observations which will be presented 

 I prefer to term this phenomenon the inhibitive reaction, and to assume, for 

 facility of expression alone, that it is evidence of what may be called 

 inhibitin. In contrast to the conception that sensitisers* (amboceptors) show, 

 in the presence of their specific antigens, complement attraction, inhibitin 

 may be said to exert a complement negation effect. 



2. Fixation Reaction. — Sera with these effects (sensitisers, amboceptors) 

 must cause deflection of complement with the antigenic as well as with all 

 other dilutions. 



3. Indifferent Reaction. — The essential features here are complete hsemolysis 

 with the antigenic, and no haemolysis with the full anti-complementary 

 dilution. The varying results which were obtained with the intermediate 

 dilutions and these sera first demonstrated the importance of two factors 

 (serum suspension and natural sheep-corpuscle amboceptor) which should 

 always be controlled. When these are offset, many irregularities, especially 

 noticeable with varying amounts of serum in the inhibitive reaction and the 

 reaction of fixation, are explicable, while " doubtful reactions " also can to a 

 great extent be eliminated. 



From the prevalence of tuberculosis in adults, I have been forced to show 

 the specificity of the inhibitive or fixation reactions by the use of other 



* The terms " amboceptor " and " sensitiser " have been used with the same meaning. 

 In referring to tuberculous fixation bodies, it has been convenient to use the word 

 "sensitiser," reserving the term "amboceptor" for other than tuberculous fixation bodies. 



