296 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



3. Blood serum containing complement. This is usually 

 obtained from the guinea pig. It is carefully titrated 

 before use in order to determine the amount of complement 

 present. 



Suitable amounts of numbers one, two and three, that is, 

 of the antigen, serum containing amboceptor, and serum 

 containing complement are mixed. The amboceptor should 

 at once unite with the specific organism, such as the 

 glanders bacillus, and then the complement unite with this 

 sensitized antigen. Theoretically one might expect to 

 determine the presence of amboceptor then by examining 

 such material microscopically. Practically, however, this 

 does not prove to be feasible. The changes brought about 

 by the complement in the bacteria may be in some cases so 

 slight that they cannot be observed microscopically. It will 

 be noted, however, that if amboceptor is present the comple- 

 ment will be used up or fixed. If amboceptor is not present 

 the complement will not be fixed. To determine then, 

 whether or not the amboceptor is present, some reagent is 

 desirable which may be added to this mixture to determine 

 whether or not the complement has disappeared. This 

 reagent (the second group of materials) is prepared from 

 the following: 



4. Red blood cells of some suitable animal such as sheep. 

 These should be washed carefully and suspended in 

 physiological salt solution. 



5. Serum from rabbit which has been immunized by 

 repeated injection of sheep red blood corpuscles. This is 

 heated to destroy any complement present. It should con- 

 tain amboceptors specific for sheep red blood cells. 



Number four and five are mixed. The amboceptor unites 

 with the red blood cells, sensitizing them to complement. 

 These sensitized cells may now be used as an indicator in 

 solutions for the presence or absence of complement. This 

 mixture of 4 and 5 is added to the first mixture, containing 



