426 BACTERIOLOGY. 



The results obtained in the health department labor- 

 atories, as well as elsewhere, have shown that in a 

 certain proportion of cases not typhoid fever there 

 occurs a delayed moderate reaction in a 1 to 10 dilution 

 of serum or blood (the proportion originally proposed 

 by Widal); but very rarely, if ever, excepting in 

 typhoid fever, or at least typhoid infection, does a 

 complete reaction occur in this dilution within jive 

 minutes. When dried blood is used the slight ten- 

 dency of non-typhoid blood in 1 to 10 dilution to 

 produce agglutination is increased by the presence of 

 the fibrinous clumps, and perhaps by other substances 

 derived from the disintegrated blood-cells. From many 

 cases examined by Fraenkel, Stern, Forster, Scholtz, 

 ourselves and others, it has been found that in dilutions 

 of 1 to 20 or more a decided, quick reaction is never 

 produced in any febrile disease other than that due to 

 typhoid infection, while in typhoid fever such a distinct 

 reaction often occurs with dilutions of 1 to 50. 



The mode of procedure, therefore, as now employed 

 is as follows : The test is first made with the typhoid 

 bacillus in a 10 per cent, solution of serum or blood. 

 In the case of serum, one part of serum is added to 

 nine of the bouillon culture. With dried blood, a solu- 

 tion of the blood is first made, and the final dilution 

 guessed from the color of the mixed culture and blood 

 solution. To obtain an idea of the dilution by the 

 color, known amounts of blood are dried and then 

 mixed with definite amounts of water ; the colors re- 

 sulting are fixed in the memory as guides for future 

 tests. If there is no reaction that is to say, if 

 within five minutes no marked change is noted in the 

 motility of the bacilli, and no considerable clumping 



