348 TYPHOID FEVER. 



be of value in giving confirmation to other tests. There is 

 a point in this connection regarding which further light is 

 required. Many races of B. coli in use have been isolated 

 from typhoid cases, and we as yet do not know what effect 

 a sojourn in such circumstances may have on its subsequent 

 sensitiveness to agglutination by typhoid serum. 



The discovery that the exhibition of Widal's reaction is 

 not confined to the B. typhosus has caused great attention 

 to be paid to the sensitiveness to different sera shown by 

 it and by other allied organisms. It has been found that 

 not only typhoid sera but the sera of healthy persons, and 

 of those suffering from diseases other than typhoid fever, 

 may occasionally clump typhoid bacilli even when con- 

 siderably diluted. It has not, however, been sufficiently 

 noted that, as Christophers has pointed out, a large pro- 

 portion of similar sera will clump the B. coli in dilutions of 

 from i : 20 to i : 200, and no doubt many of the reactions 

 shown by typhoid sera towards B. coli are due to the pre- 

 existence in the individuals of an agglutinative property 

 towards the bacillus. It has been shown that both the 

 B. coli and the B. typhosus are clumped by the normal 

 serum of the horse, the ass, and the rabbit, and it has been 

 found that the serum of an animal immunised against either 

 of these bacilli sometimes clumps both, and sometimes also 

 in addition the B. enteritidis, though usually the dilutions 

 necessary differ. It may also be remarked that in such 

 immunised animals the best agglutinating result is not 

 always obtained with subcultures of the race by which im- 

 munisation was effected. It is evident that these results 

 are of great interest, and may ultimately throw light on 

 the true nature of agglutination. 



With regard to the value of the serum reaction there is 

 little doubt. In nearly 95 per cent of cases of typhoid it 

 can be obtained in such a form that no difficulty is 

 experienced if the precautions detailed above are observed. 

 The causes of possible error may be summarised as follows : 

 the serum of the person may naturally have the capacity of 

 clumping typhoid bacilli ; there may have been an attack 



