340 TYPHOID FEVER 



typhoid, but cases occur in which it may permanently disappear 

 before convalescence sets in. How long it lasts after the end of 

 the disease has not yet been fully determined, but in many cases 

 it has been found after several months or longer. As a rule, up 

 to a certain point, the reaction is more marked where the fever 

 is of a pronounced character, whilst in the milder cases it is less 

 pronounced. In certain grave cases, however, the reaction has 

 been found to be feeble or almost absent, and accordingly some 

 hold that (a feeble reaction when the disease is manifestly severe 

 is of bad omenj In some cases which from the clinical symptoms 

 were almost certainly typhoid, the reaction has apparently been 

 found to be absent. Such cases should always be investigated 

 from the point of view of their possibly being paratyphoid fever. 



It has been found that the reaction is not only obtained with 

 living bacilli, but in certain circumstances also with bacilli 

 that have been killed by heating at 60 C. for an hour, if 

 a higher temperature be used, sensitiveness to agglutination is 

 impaired. The capacity is also still retained if a germicide be 

 employed. Here Widal recommends the addition of one drop of 

 formalin to 150 drops of culture. The reaction, however, tends 

 to be less complete. 



Besides the blood serum it has been found that the reaction 

 is given in cases of typhoid fever by pericardial and pleural 

 effusions, by the bile and by the milk, and also to a slight 

 degree by the urine. The blood of a foetus may have little 

 agglutinating effect though that of its mother may have given 

 a well-marked reaction ; sometimes, however, the foetal blood 

 gives a well-marked reaction. It may here also be mentioned 

 that a serum will stand exposure for an hour at 58 C. without 

 having its agglutinating power much diminished. Higher tem- 

 peratures, however, cause the property to be lost. 



The Agglutination of Organisms other than the B. Typhosus 

 by Typhoid Serum. It was at first thought that' the reaction in 

 typhoid fever would afford a reliable method of distinguishing 

 the typhoid bacillus from the b. coli. Though many races of 

 the latter give no reaction with a typhoid serum, there are others 

 which react positively. Usually, however, a lower dilution and 

 a longer time are required for a result to be obtained, and the 

 reaction is often incomplete.' It has also been found that other 

 organisms belonging to the typhoid group (v. p. 335) react in a 

 similar way. The reaction as a method of distinguishing between 

 these forms is thus not absolutely reliable, but in certain cases it 

 is of great value in giving confirmation to other tests. The im- 

 portant point here is the determination of the highest dilution 



