492 APPLICATION OF METHODS OF BACTERIOLOGY 



there is a discrepancy between the cUnical and the labora- 

 tory diagnosis in from 2 to 3 per cent, of the cases examined. 



In the hands of all who have carefully employed the 

 Widal reaction for the diagnosis of typhoid fever the results 

 are reported to have been almost uniformly satisfactory. In 

 the great majority of cases the reaction is, so far as experi- 

 ence indicates, specific — i. e., a typical reaction does not 

 occur between typhoid serum or blood and organisms other 

 than the typhoid bacillus, nor between the typhoid bacillus 

 and serums other than those of typhoid fever. There are, 

 however, confusing reactions — so-called pseudoreactions — 

 in which more or less clumping of the bacilli and a diminution 

 of motion, without complete cessation, are observed. These 

 reactions have been seen to occur with normal blood and 

 with blood from other febrile conditions. It is said by 

 Johnston and McTaggart^ that they can be prevented if 

 cultures of just the proper degree of vitality are employed; 

 and this corresponds with the results of a fairly wide per- 

 sonal experience with the test. 



In the light of present experience it is fair presumptive 

 evidence that the serum is from a case of typhoid fever 

 when unmistakable agglutination and cessation of motion 

 are seen in from fifteen to twenty minutes after typhoid 

 bacilli are mixed with the serum of a conspicuous febrile 

 condition. 



The blood of certain animals, as well as a number of 

 chemical substances, such as corrosive sublimate, alcohol, 

 salicylic acid, resorcin, and safranin in high dilution, cause 

 agglutination of the typhoid bacilli; but the reaction is 

 not specific, for in most cases they have the same effect on 

 other motile bacilli. 



' Montreal Medical Journal, March, 1897. 



