TECHNIC OF PRECIPITIN REACTIONS 337 



Tube 4: 2 c.c. of typhoid bouillon filtrate+1 c.c. of unknown serum. 

 Tube 5: 2 c.c. of typhoid bouillon filtrate+1 c.c. of typhoid im- 

 mune serum (positive control). 

 Tube 6: 2 c.c. of typhoid bouillon filtrate+1 c.c. of normal salt 



solution. 



Tube 7: 2 c.c. of typhoid bouillon filtrate+1 c.c. of normal serum. 

 Tube 8: 1 c.c. of serum+1 c.c. of normal salt solution. 

 The tubes are not shaken, and are kept at room temperature for 

 from one to six hours. If the unknown serum contains considerable 

 typhoid precipitins, a positive reaction will be noticed in the first four 

 tubes in a short time often within from ten to fifteen minutes. Tube 

 5 should show a strong reaction and the other tubes should remain clear. 

 In studying the biologic relationship of an organism to others of the 

 same group its immune serum may be used in amounts of 1 c.c. of vary- 

 ing dilutions, as 1:50, 1:100, 1:500, 1:1000, 1:2000, 1:4000, and 

 so on, with a constant dose of 1 or 2 c.c. of the bouillon filtrates of the 

 various organisms studied. A comparison of the precipitates in the 

 respective dilutions of the different filtrates indicates the relationship, 

 according to the amount of group precipitins present in the immune 

 serum. 



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