422 BACTERIOLOGY. 



from the typhoid organism often a matter that requires 

 the careful application of all the different tests. 



THE AGGLUTINATION KEACTION. The nearest ap- 

 proach to a trustworthy means of identification is the 

 reaction of typhoid bacilli with the blood of typhoid 

 subjects, and in so far as can be said now, this reaction 

 is specific. When typhoid bacilli are brought in con- 

 tact with the blood-serum from human beings sick of 

 typhoid fever, or from animals that have survived in- 

 oculation with cultures of this organism, there occurs 

 a peculiar alteration in the relation of the organisms to 

 one another in the fluid. As ordinarily seen in a hang- 

 ing drop of bouillon, the typhoid bacilli appear as single, 

 actively motile cells ; when to such a drop a little dilute 

 serum from a case of typhoid fever is added the motility 

 of the bacteria gradually lessens and finally ceases, and 

 they then congregate, "agglutinate 7 ' in larger and 

 smaller clumps, or if one add to 4 or 5 c.c. of a twenty- 

 four-hour-old bouillon culture of typhoid bacilli in a 

 narrow test-tube about eight drops of serum from a case 

 of typhoid fever and maintain this mixture at body tem- 

 perature the normally clouded culture will be seen after 

 a few hours to have undergone a change; instead of a 

 diffuse clouding it is clear and flocculent masses of the 

 bacteria that have agglutinated together as a result of 

 the specific action of the serum used will be scattered 

 about in it. 



For the hanging-drop test, sufficient serum may be 

 obtained from a needle-prick in the finger, while for 

 the test-tube reaction a larger amount is needed ; this 

 may be obtained from blood drawn from a superficial 

 vein by means of a hypodermic syringe, or from the 



