SERUM DIAGNOSIS. 347 



certainly typhoid, the reaction has apparently been found 

 to be absent. 



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. This last may be effected 

 by keeping the bacilli at 60 C. for an hour. If a higher 

 temperature be used, sensitiveness to agglutination is im- 

 paired. 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. It may be remarked 

 that while clumping is taking place where dead cultures are 

 used, active Brownian movement among the free bacteria 

 may be noticed, which may lead the observer to doubt 

 whether the bacilli are really dead. 



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. 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 temperatures, however, cause 

 the property to be lost. 



The Agglutination of Organisms other thcui the B. 

 Typhosus by Typhoid Serum. It was at first thought that re- 

 action in typhoid fever would afford a reliable method of dis- 

 tinguishing 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 low r er dilution and a longer time are required 

 for a result to be obtained, and the reaction is often in- 

 complete. It has also been found that other organisms 

 belonging to the typhoid group, e.g., Gaertner's bacillus and 

 perhaps the bacillus of psittacosis, react in a similar way. 

 The reaction as a method of distinguishing between 

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



