AGGLUTINATION OF OTHER BACILLI. 345 



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 cir- 

 cumstances may have on its subsequent sensitiveness to agglu- 

 tination by typhoid serum. 



The discovery that the exhibition of agglutination is not 

 confined to the B. typhosus has caused great attention to be 

 paid to the sensitiveness to different sera shown by it and Uy 

 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 considerably diluted. It has not, 

 however, been sufficiently noted that, as Christophers has 

 pointed out, a large proportion of similar sera will clump the 

 B. coli in dilutions of from 1-20 to 1-200, 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 prop- 

 erty towards the bacillus. It has been shown that both the 

 B. coli and the B. typhosus may be 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 ad- 

 dition the B. enteritidis, though usually the dilutions necessary 

 differ. It may also be remarked that in such immunised ani- 

 mals the best agglutinating result is usually obtained with sub- 

 cultures of the race by which immunisation was effected. 



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 pos- 

 sible 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 of typhoid fever pre- 

 viously with persistence of agglutinative capacity ; the case may 

 be one of disease caused by an allied bacillus ; the disease may 

 have a quite different cause, r d yet the serum may react with 

 typhoid bacilli ; the disease may be typhoid fever and yet no 

 reaction may occur. The most important of these sources of 

 error is that with which diseases caused by allied organisms are 



