WIDAL'S REACTION 



251 



of blood and bacilli is watched under the micro- 

 scope : — 



"The motility of the bacilli is instantaneously 

 or very quickly arrested, and in a few minutes the 

 bacilli begin to aggregate together into clumps, and 

 by the end of the half-hour there will be very few 

 isolated bacilli visible. In less marked cases, the 

 motility of the bacilli does not cease for some 

 minutes : while in the least marked ones the motility 

 of the bacilli may never be completely arrested, but 

 they are always more or less sluggish, while clump- 

 ing ought to be quite distinct by the end of the 

 half-hour." 



The result of this clumping is also plainly 

 visible to the naked eye, by the subsidence 

 of the agglutinated bacteria to the bottom of the 

 containing vessel : and thus an easy practical mode 

 of diagnosis is afforded by it. 



As with typhoid, so with Malta fever, cholera, 

 and some other infective diseases. And the unim- 

 aginable fineness of this reaction goes far beyond 

 the time of the disease. Months, even years, after 

 recovery from typhoid, a fiftieth part of a drop of 

 the blood will still give Widal's reaction : and it 

 has been obtained in an infant whose mother had 

 typhoid before it was born. A drop of dried blood, 

 from a case suspected to be typhoid, may be sent a 

 hundred miles by post to be tested ; and typhoid, 

 like diphtheria, may now be submitted to the 

 judgment of an expert far away, and the answer 

 telegraphed back. It would be difficult to 

 exaggerate the practical importance of this reaction 



