THE MACROSCOPICAL REACTION 387 



Three test-tubes containing the 10, i, and o.i per cent, solutions 

 of specific serum (about 90 c. mm. remaining in each) . 

 Tube containing 50 per cent, solution of pooled serum. 

 Sedimentation pipettes (vide page 1 7) or teat pipettes. 



METHOD. 



1. Pipette 90 c. mm. of the bouillon culture into each 

 of the tubes containing the diluted serum; and the 

 same quanitity into the tube containing the pooled 

 serum. 



2. Fill a sedimentation tube (by aspirating) or a teat 

 pipette from the contents of each tube. Seal off the 

 lower ends of the sedimentation tubes in the Bunsen 

 flame. 



3 . Label each tube with the dilution of serum that it 

 contains viz., 5, 0.5, and 0.05 per cent. 



4. Place the pipettes in a vertical position, in a 

 beaker, in the incubator at 37 C., for one or two hours. 



5. Observe the granular precipitate which is thrown 

 down when the reaction is positive, and the uniform 

 turbidity of the negative reaction as compared with the 

 appearances in the control pooled serum. 



OPSONIN. 



Opsonin is the term applied by Wright to a substance, 

 present in the serum of an inoculated animal, which is 

 able to act upon or sensitise bacteria of the species 

 originally injected, so as to render them an easy prey 

 to the phagocytic activity of polymorphonuclear leuco- 

 cytes. In the method for demonstrating opsonin about 

 to be described, a comparison is made between the 

 opsonic " power" of the pooled serum and the specific 

 serum. 



Apparatus: 



Small centrifuge and tubes for same (made from the barrels 

 of broken capillary pipettes by sealing the conical ends in the 

 bunsen flame). 



Capillary Pasteur pipettes. 



India-rubber teats. 



