344 TYPHOID FEVER. 



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 omen. In some cases, which from the clinical symp- 

 toms were almost 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 impaired. The capacity is also 

 still retained if a germicide be employed. Here Widal recom- 

 mends the addition of one drop of formalin to 150 drops of cul- 

 ture. 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 movements 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 ; 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 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, 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 be of value 



