SERUM DIAGNOSIS 373 



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. 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. Dreyer has introduced a simple technique which 

 enables an ordinary practitioner provided with dead cultures to 

 carry out the test for himself. 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 }>ower much diminished. Higher 

 temperatures, however, cause the proj>erty to be lost. 



The Agglutination of Organisms other than the B. TyphoxuK 

 ly 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. 382) 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 

 important point here is the determination of the highest dilution 

 with which clumping is obtained (for methods, see p. 120). 

 There is a point in this connection regarding which further 



