BACTERIAL SUSPENSION. 213 



ing 5 or 10 c.c. of physiologic salt solution into 

 the tube and shaking vigorously; the resulting 

 suspension is then ready for use. For either the 

 macroscopic or microscopic test it is absolutely 

 essential to have a homogeneous suspension of the 

 bacteria., in order to avoid misinterpretations which 

 may be occasioned by the accidental or natural 

 bacilli were agglutinated before they were injected 

 should be shaken thoroughly before the emulsions 

 are used. This uniformity of suspension is readily 

 accomplished with such organisms as the typhoid 

 bacillus and cholera vibrio,, motile organisms^ but 

 when they grow in chains (streptococcus) or in 

 coherent masses (diphtheria and tubercle bacilli) 

 more violent measures must be resorted to. Daily 

 shaking of a liquid culture of the diphtheria or 

 tubercle bacillus is fairly effective, but the medium 

 must be passed through a paper filter before it can 

 be used safely; in this way the larger clumps are 

 removed. Some investigators dry a large quantity 

 of tubercle bacilli, grind them up thoroughly in an 

 agate mortar and suspend the particles in salt 

 solution; the fragmented condition of the organ- 

 isms does not interfere with their participation in 

 the reaction. One should have a uniform technic 

 in preparing a bacterial emulsion in order to obtain 

 as nearly as possible the same number of bacteria 

 in a given volume of solution, on different occa- 

 sions. For example, one may uniformly suspend 

 a twenty-four-hour agar culture in 10 c.c. of salt 

 solution. A uniform technic makes it possible to 

 observe the quantitative relationship which exists 

 between the mass of bacteria to be agglutinated 

 and the agglutinating power of the serum. 



