3o6 



MANUAL OF BACTERIOLOGY. 



In using, melt in a water-bath; add normal sodium hydrate till the reaction 

 is slightly alkaline to htmus-paper. Add 20 c.c. Merck's litmus solution. 

 Also add 3 drops of a t per cent, alcoholic solution of crystal violet. Mix 

 thoroughly. Pour into Petri dishes, and use as in the original method. 



M. W. Richardson has devised an application of the serum-test to plate- 

 colonies suspected of containing typhoid bacilK. If a typhoid colony be torn 

 with a needle, under moderate magnification "a seething motion resembling 

 much the appearance of a swarm of bees" may be seen. This appearance is 

 due to the motility of the bacteria. If such a colony be touched with a small 

 quantity of blood-serum from a case of typhoid fever, the motion is said to cease 

 instantly and almost absolutely. Colonies of other motile bacteria do not 

 undergo a corresponding loss of motility. 



Fig. 92. — Application or the Sekum-reaction to Typhoid Bacilli. 

 shows the distribution of the bacilli before the reaction. It is to be re- 

 membered that they are motile and their positions may change continu- 

 ally. B shows clumping of the motionless bacilli after mixture with the 

 serum of a case of typhoid fever. (Diagrammatic.) 



The Seritm-test for Typhoid Fever.* 

 When a small quantity of a culture of typhoid bacilli is mixed with a, little 

 blood-serum derived from a case of typhoid fever, within a few minutes the 

 motility of the typhoid bacilli ceases and they become agglutinated into clumps 

 ormasses (see Agglutinins, Bacterial Poisons, page 166). The bacilli may event- 

 ually undergo disintegration into granular material (see Lysins,Bacterial Poisons, 

 page 166). This reaction rarely takes place vidth the blood-serum of healthy 



* This test is often known as the "Widal reaction." For a history and 

 general discussion of the subject see Durham. Journal of Experimental Medi- 

 cine. Vol. V. P. 353. 



