BACILLUS TYPHOSUS 489 



from human beings sick of typhoid fever, or from animals 

 that have survived inoculation with cultures of this organ- 

 ism, there occurs a peculiar alteration in the relation of the 

 organisms to one another in the fluid. As ordinarily seen 

 in a hanging 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" 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 temperature 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 floccu- 

 lent 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 cleansed skin by a wet- 

 cup, or, better still, from a small cantharides or ammonia 

 blister. 



It is proper to state, however, that occasionally cultures 

 of genuine typhoid bacilli are encountered that do not 

 respond to this peculiar influence of typhoid blood, even 

 though the blood be tested at different stages of the disease, 

 and even though it may cause the characteristic cessation 

 of motion and clumping with other cultures of this organism 

 upon which it is tried. 



