120 LABORATORY GUIDE IN BACTERIOLOGY 



/) Make a control hanging drop without serum to 

 test the motiUty and the absence of clumps. 



g) When the clumping is completed allow the drop 

 to dry in the air without stirring or spreading, fix in the 

 flame, or better with absolute alcohol, and stain with 

 gentian violet. A permanent preparation can be 

 obtained in this manner, showing the agglutinated 

 bacteria. 



Blood may also be obtained by puncturing the lobe 

 of the ear and collecting the blood in a capillary glass 

 tube with a small bulb. Hold the bulb down, fill 

 three-fourths with blood, and seal the ends in the 

 flame. In 45 minutes the serum will have separated, 

 and may be tested. 



The above-described method of an agglutination 

 test is known as the microscopic test. Another 

 method, in which larger amounts of serum and suspen- 

 sion are required, is known as the macroscopic method. 

 Small test tubes are used, and- definite amounts of 

 ba:terial suspensions are introduced, by means of 

 graduated pipettes. The serum is then added in vary- 

 ing amounts so as to effect the desired dilutions (see 

 table in appendix, p. 197). The tubes are then incu- 

 bated at 37° C, usually for 2 hours. After this they 

 are placed in an ice -chest for sedimentation. If com- 

 plete agglutination has taken place, the bacteria will 

 have collected in clumps at the bottom, forming a 

 sediment. The supernatant fluid is clear. By varying 

 amounts of sediment and varying degrees of turbidity 

 of the supernatant fluid, the degree of agglutination 

 may be estimated. A control tube of a bacterial 

 suspension without addition of serum serves as a guide. 

 Controls with normal serum should also be made. 



