BACILLUS TYPHOSUS. 423 



cleansed skin by a wet-cup, or, better still, from a 

 small cantharides or ammonia blister. 



It is proper to state, however, that occasionally cult- 

 ures 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 charac- 

 teristic cessation of motion and clumping with other 

 cultures of this organism upon which it is tried. 



" WIDAL/S REACTION." When employed conversely 

 i. e., for deciding if the serum used is from a case of 

 typhoid fever or not the reaction constitutes "WidaPs 

 serum diagnosis of typhoid fever." In beginning these 

 tests it is often necessary to try several cultures of gen- 

 uine typhoid bacilli from different sources and of vary- 

 ing degrees of vitality, before a strain is procured that 

 reacts conspicuously and quickly with genuine typhoid 

 serum. 



WIDAL'S REACTION WITH DRIED BLOOD. This 

 reaction can also be obtained with redissolved dried 

 blood i. e., by the Johnston method : a drop of the blood 

 to be tested, obtained by a needle-prick in the cleansed 

 finger or lobe of the ear, is collected on a bit of clean, 

 unglazed paper and allowed to dry. The paper is then 

 folded, kept free from contamination, and taken to the 

 laboratory. With a medium-size platinum-wire loop a 

 drop of sterile bouillon, water, or physiological salt solu- 

 tion is gently rubbed upon the drop of dried blood until 

 the contents of the loop are of a dark amber color ; this 

 is then mixed with a drop of bouillon culture of typhoid 

 bacilli on a cover-glass, which is mounted upon the 

 hollow-ground slide as a hanging drop, when the effect 



