TESTING AGGLUTINATIVE POWER OF SERUM. Ill 







I. 



V>:?y 



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 -a^ 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 should 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 

 sHde, 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. 



