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 five 
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 fibrincus 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 
