278 BACILLUS TYPHOSUS. 



(1) The colon bacillus coagulates milk ; the typhoid does 

 not. 



(2) The colon bacillus evolves gas, especially in media con- 

 taining grape-sugar ; the typhoid does not. 



(3) The colon bacillus gives the indol reaction^ when grown 

 in Dunham's solution ; the typhoid ^oeTnot. ~ 



(4) The colon bacillus is distinctly acid-producing ; the 

 typhoid usually produces no acid or 6nlyar~Very" "slight 

 amount. 



Occasionally, however, varieties of either organism are met 

 with that do not answer to these specific reactions, so that the 

 differentiation can never be said to be absolute. The Widal 

 test might be of assistance, but even here variations may 

 occur. Pfeiffer's phenomenon is also of value in the differ- 

 entiation. 



When the bacillus is obtained from the spleen, the cultures 

 are made from the fluid obtained from this organ. The 

 method of puncture is the same as that used in all explora- 

 tory punctures, but the danger from sepsis is much greater, 

 because the typhoid bacillus is capable of causing suppura- 

 tion. The wound in the spleen may be the starting-point of 

 a fatal septic peritonitis. 



Widal reaction : A most valuable aid in the clinical diag- 

 nosis of typhoid fever is the Widal reaction or the agglutina- 

 tion-test. It is not an absolute test, but when carefully and 

 properly performed it is of considerable diagnostic value. 

 The blood-serum of the typhoid patient mixed with a pure 

 culture of the typhoid bacilli yields the agglutination phe- 

 nomenon of Gruber. The blood is obtained through an 

 aseptic puncture of the tip of a finger or the lobe of the ear, 

 or directly from a vein. If the blood thus obtained is not to 

 be used immediately, it is allowed to coagulate on a sterile 

 piece of isinglass ; or in an emergency, on a piece of paper or 

 on blotting-paper. The blood-serum retains its agglutinating 

 power for months, and may, therefore, be sent any distance 

 for diagnosis. 



The test, as a rule, is not applicable until after the first 

 week. Fraenkel observed the reaction in one case on the 

 second day. It disappears during convalescence, although in 



