QUALITATIVE BACTERIOLOGICAL ANALYSIS. 179 



of different races of the B. typhosus, before it is used to 

 diagnose an unknown bacillus. A serum which fails to agglutinate 

 the stock cultures when used in a dilution of 11000 should be 

 rejected as being too weak to secure satisfactory results. 



(3) The Time during which the Serum is allowed to Act on the 

 Bacillus. The third factor of the agglutination reaction becomes 

 of great importance when weak anti-typhoid sera are employed. 

 If a quickly acting powerful serum is used for the test the time 

 limit of two hours is quite sufficient for all practical purposes. 

 But sometimes a powerful serum cannot be obtained, and 



POWEEFUL ANTI-TYPHOID SEBUM. 



WEAK ANTI-TYPHOID SEBUM. 



The sign + indicates complete agglutination. 



incomplete agglutination (large clumps, but a few 



motile bacilli). 

 ., no trace of agglutination. 



