QUALITATIVE BACTERIOLOGICAL ANALYSIS. 181 



emulsion with broth, and examine in a hanging-drop. This is 

 called the rapid method as compared with the two former, 

 which are slow methods. 



(d) Wright has introduced a method of making the dilutions 

 by means of glass capillary pipettes. Normal salt solution is 

 used to dilute the serum, and a twenty-four hours agar growth 

 of B. typhosus is made into an emulsion with normal salt solu- 

 tion. The dilutions of serum, thoroughly mixed with an equal 

 volume of emulsion (which, of course, doubles the dilution of 

 serum already prepared), are placed in capillary pipettes, which 

 are then sealed at one end and kept at the room temperature 

 for twenty-four hours. When agglutination is " complete" the 

 bacilli are found as a firm sharply- outlined mass at the bottom 

 of the pipette ; if, however, the agglutination is " incomplete " 

 granular masses are seen throughout the tube. The appearances 

 must always be compared with a control tube containing only 

 the emulsion diluted with an equal volume of salt solution, which 

 has been left at the room temperature for the same time. 



Wright's method of making the dilutions is admirable, but I 

 have often found that when normal salt solution is used to make 

 the emulsion, and also to dilute the serum, the sharpness or 

 sensibility of the reaction is much diminished. The following 

 method of procedure is therefore recommended : 



Place a little of the anti-typhoid serum in a watch-glass, 

 insert the point of a capillary tube in the fluid and allow this to 

 run up the tube for about an inch and a half, mark on the 

 glass with a wax pencil the upper limit of the fluid, and then 

 blow out the serum into a watch-glass. Next dilute the serum 

 1-5. This is easily done by inserting the point of the pipette 

 in a little sterile broth (contained in a watch-glass), which is 

 allowed to run up to the mark on the tube. The broth is then 

 blown out into the watch-glass containing the serum, three 

 other equal quantities of broth, obtained in the same manner, 

 are next added to the serum, and the broth and serum are then 

 thoroughly mixed. Some of the dilution of 1-5 is now converted 

 into 1-25, by taking a portion of the 1-5 dilution and adding to 

 it four equal portions of broth. The 1-25 dilution is made into 

 1-50 by taking a portion and mixing with it an equal portion 

 of broth. The 1-50 dilution is converted into a dilution of 



