TYPHOID BACILLUS 341 



blood cells appear in the field viewed under the microscope. Fresh 

 whole blood presents one great disadvantage the fibrin in it may 

 cause a pseudoagglutination, for the fibrin network that forms as 

 coagulation proceeds entangles typhoid bacilli in its meshes, giving 

 the appearance of a true agglutination. Whole blood can be con- 

 veniently drawn into a blood-counting pipette and diluted accurately 

 and immediately. 



The Culture to be Used. Old stock cultures of typhoid bacilli usually 

 give the best results. Freshly isolated cultures not infrequently agglu- 

 tinate less readily than those which have been on artificial media for 

 some time. The organisms should be grown in 0.1 per cent, dextrose 

 broth for eighteen hours at 30 to 32 C. It has been found that 

 typhoid bacilli grown at this temperature agglutinate somewhat 

 better than those grown at 37 C. Killed cultures are frequently 

 used, but the results obtained are somewhat less accurate than those 

 with living cultures. In rare instances it has been found that killed 

 cultures will agglutinate with typhoid sera at 45 C. when living 

 cultures fail to agglutinate. Controls must always be made: the 

 typhoid culture is diluted with an equal volume of salt solution. 

 Spontaneous agglutination sometimes takes place when no serum is 

 present. This is shown in the control and at once invalidates the 

 agglutination w r hich may be obtained with the serum. 



Technic of Test. (A) Microscopic Method. Dried blood, blood 

 serum, blister fluid, or whole blood is diluted 1 to 20 with physiological 

 salt solution. A loopful of this diluted fluid is mixed intimately with 

 a loopful of typhoid broth culture on a coverglass and suspended in 

 a hanging drop slide ringed with vaseline to prevent evaporation. 

 The final dilution of the blood is 1 to 40 by this procedure. A control 

 is made using a loopful of salt solution and a loopful of typhoid culture 

 prepared in the same manner. Both the serum and the control are 

 kept at room temperature. A preliminary examination should show 

 actively motile bacteria in the control preparation and usually actively 

 motile bacteria in the serum preparation. It sometimes happens that 

 agglutination takes place in the serum preparation almost immediately. 

 If the preliminary examination is satisfactory, the final examination 

 is made at the end of an hour. Both preparations are examined and 

 the controls should show actively motile unclumped organisms. A 

 positive agglutination is recorded if the control is as stated and the 

 organisms in the serum preparation are non-motile and gathered 

 together in clumps with few or no free-swimming bacteria between 

 the clumps. 



