118 



METHODS OF EXAMINING SERUM 



r 



ing power of a serum is to be tested — expressed as the highest dilution in 

 which it produces complete sedimentation within twenty-four hours— a 

 standard quantity (by weight) of bacteria must be added to a given 

 quantity of bouillon. This is not necessary for clinical diagnosis.) 

 4. To test microscopically, mix equal quantities (measured by a marked 



capillary pipette) of the 

 diluted serum and the 

 bacterial emulsion on a 

 glass slide, cover with a 

 cover -glass, and examine 

 under the microscope. The 

 form of glass slide used for 

 hang-drop cultures (Fig. 25) 

 will be found very suitable. 

 The ultimate dilution of 

 the serum will, of course, be 

 double the original dilution. 

 To observe sedimentation, 

 mix equal parts of diluted 

 serum and of bacterial 

 emulsion, and place in a 

 thin glass tube — a simple 

 tube with closed end or a 

 U-tube. Keep in upright 

 position for twenty -four 

 hours at room temperature, 

 or at 55° C. in a water 

 bath for two hoUrs. One 

 of Wright's sedimentation 

 tubes is shown in Fig. 40, d. 

 Diluted serum is drawn up 

 to fill the space rnn, a small 

 quantity of air is sucked up 

 after it to separate it from 

 the bacterial emulsion, 

 which is then drawn up in 

 the same quantity ; the 

 diluted serum will then 

 occupy the position hi. 

 The fluids are then drawn 

 several times up into the 

 bulb, and returned to the 

 capillary tube so as to mix, 

 and finally blown carefully 

 down close to the lower 

 end, which is then sealed 

 off. The sediment collects 

 at the lower extremity. 

 It is often important to observe not merely the fact that agglutination 

 occurs, but also the weakest concentration of the serum with which the 

 reaction can be obtained. 



Standard Cultures. — Dreyer has introduced a method of standardising 

 agglutinable cultures, the organisms being killed by formalin. 



The bacillus (b. typhosus, b. paratyphosus, etc.) is grown for twenty- 



Fig. 40. — Tubes used in testing agglutinating 

 and sedimenting properties of serum. 



