630 A MANUAL OF BACTERIOLOGY 



In the antigen series, the same causes may act, the antigen may 

 be too strong, or the sample of guinea-pig serum be anti-comple- 

 mentary. 



Controls. Though it is not absolutely necessary to put up a 

 control with negative and positive sera, this procedure serves as 

 an additional safeguard that everything is working properly. In 

 ordinary practice, a positive serum from the last batch of speci- 

 mens is kept in the ice-chest for the test the following week. It 

 is preferable to choose as a control a positive serum possessing 

 medium fixative powers, e.g. a -f + serum. The negative serum 

 may be similarly reserved from the last batch of specimens, or a 

 serum may be obtained from one of the laboratory staff on the 

 morning of the test. Both these sera, whether old or fresh, should 

 be inactivated with the other specimens on the morning of the test. 



Measurement of the Specimens and Reagents. The serum is 

 measured into the quill tubes with the throttled pipette (c), p. 624. 

 For 2, 3, or 4 volumes the pipette is once charged with the 2, 3, or 

 4 volumes respectively, and 1 volume is discharged into each tube, 

 Donald's drop method may also be used. 



For the complement-antigen and complement -saline mixtures 

 the throttled pipette (d) is used. The pipette is filled to the 

 10-volume mark, the mixture is discharged into the quill tube and 

 the tube is shaken to mix the contents. The quill tubes of the 

 size named ( 6-25 mm. ) are just large enough for the contents to be 

 mixed by shaking. If the tubes are smaller, the contents must 

 be mixed by aspirating up once and discharging, but this entails 

 rinsing the pipette every time. 



For the amboceptor-corpuscle mixture the throttled pipette (e) 

 is used. The pipette is filled to the 5- volume mark and the mixture 

 is discharged into the quill tube and the tube is shaken to mix 

 the contents. 



The serum specimens should be free from haemoglobin so far as 

 possible. The presence of . haemoglobin seems sometimes to 

 increase slightly the fixative power of the serum. 



Bacterial growth in a specimen may likewise tend to render a 

 negative serum positive. 



It is not necessary to put up a saline tube as well as an antigen 

 tube with each specimen, but any specimen which reacts positively 

 in antigen must also be tested in saline to ascertain that it does not 

 fix without antigen. 



