TESTING AGGLUTINATIVE POWER OF SERUM. 



Ill 



way and added till the requisite dilution is obtained. (c} By means of a 

 platinum needle with a loop at the end (Deldpine's method). A loopful of 

 serum is placed on a slide, and the desired number of similar loopfuls of 

 bouillon are separately placed around on the slide. The drops are then mixed. 

 A very convenient and rapid method of combining the steps i and 2 is to 

 draw a drop of blood up to the mark i or .5 on a leucocytometer pipette and 

 draw the bouillon after it till the bulb is filled. A dilution of 10 or 20 times 

 is thus obtained. Then blow the mix- 

 ture into a U-shaped tube (Fig. 53, c) 

 and centrifugalise or simply allow the 

 red corpuscles to separate by stand- 

 ing. (In this method of course the 

 dilution is really greater than if pure 

 serum were used, and allowance must 

 therefore be made in comparing re- 

 sults.) The presence of red corpus- 

 cles is no drawback in the case of 

 the microscopic method, but when 

 sedimentation tubes are used the cor- 

 puscles should be separated first. 



3. The bacteria to be tested 

 should be taken from young cultures, 

 preferably not more than twenty-four 

 hours old, incubated at 37 C. They 

 may be used either as a bouillon 

 culture or as an emulsion made by 

 adding a small portion of an agar 

 culture to bouillon. In the latter 

 case the mass of bacteria on a plati- 

 num loop shoujd be gently broken 

 down at the margin of the fluid in a 

 watch-glass. When a thick turbidity 

 is thus obtained, any remaining frag- 

 ments should first be removed and 

 then the organisms should be uni- 

 formly mixed with the rest of the 

 fluid. The bacterial emulsion ought 

 to have a faint but distinct turbidity. 

 (When the exact degree of sediment- 

 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 stand- 

 ard 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 hanging-drop cultures (Fig. 34) will be found very suitable. 

 The ultimate dilution of the serum will, of course, be double the original dilution. 



FIG. 53. Tubes used in testing agglutinating 

 and sedimenting properties of serum. 



