70 



LABORATORY COURSE IN SERUM STUDY 



immune animal serum is used this should previously be diluted about 

 1-100). Mix this dilution of serum thoroughly by drawing it in and out 

 of the pipette several times. Then place 5 drops of this first dilution 

 in the second watch glass. Mix the contents of the second glass as 

 before. Place 5 drops from the second glass in the third glass ; return 

 the remainder of the fluid to the second glass, mix the contents of the 

 third watch glass and remove 5 drops of this last to make its volume 

 equal to that of the others. We now have four watch glasses, each con- 

 taining 5 drops of fluid, representing 1-10, 1-20, 1^0 dilutions of the 

 serum in the first three, and salt solution in the fourth. The pipette is 

 now thoroughly rinsed with salt solution and filled with the typhoid 

 broth. Five drops of the broth are allowed to fall into each of the 

 watch glasses, reducing the dilutions to 1-20, 1^0, and 1-80. These are 

 the usual dilutions used in the Widal test for diagnosis. By means 

 of a platinum loop a series of hang-drop preparations is then made, 

 first with the control, then of the highest dilution, etc. The drops are 

 allowed to stand at room temperature for an hour and are then studied 

 under a high, dry lens of a microscope and the completeness of the clump- 

 ing and the loss of motility in the different preparations recorded. 



Discard 5 drops of Mixture No. 3 and add 5 drops of a broth culture 

 of B. typhosus to each glass. 



B 



A similar test, using the same reagents, measured by the Wright 

 technique, should also be set up : 



Take four watch glasses as before and a capillary pipette, broken off, 

 squarely tipped, stoppered with cotton, and provided with a rubber 

 nipple. Place a mark with a wax pencil about one inch from the tip of 

 the pipette. Pour out salt solution into a watch glass or cover of a 

 Petri dish so that it is easily reached with a pipette. Draw up salt solu- 

 tion to the mark, admit a bubble of air, draw up salt solution again to the 

 mark, admit a bubble of air, and proceed until 9 units of salt solution have 

 been taken up. Then take up serum to the mark and discharge the 



