BACILLUS TYPHOSUS. 425 
good for diagnostic purposes from the dried blood as 
from the serum. 
The Typhoid Culture Employed. It is important that 
the culture employed for serum-tests should be a suit- 
able one, for although in our experience all cultures 
show the reaction, yet some respond much better than 
others. A broth culture of the typhoid bacillus de- 
veloped at 35° C., not over twenty-four hours old, in 
which the bacilli are isolated and actively motile, has 
been found to give us the most satisfactory results. 
Stock cultures of typhoid bacilli can be preserved on 
nutrient agar in sealed tubes and kept in the ice-hox. 
These remain alive for months or even years. From 
time to time one of these is taken out and used to 
start a fresh series of bouillon cultures. 
The Dilution of the Blood-serum to be Employed and 
the Time Required for the Development of Reaction. The 
serum test, as has been pointed out, is quantitative and 
not qualitative. By this it is not meant to assert that the 
agglutinating and immobilizing substances produced in 
the blood of a patient suffering from typhoid infection 
are the same as those present at times in normal blood, 
or those produced in the blood of persons sick from 
other infections. It is intended, however, to maintain 
that the effect upon the bacilli, as seen under the micro- 
scope, is identical, the difference being that in typhoid 
fever, as a rule, substances which cause this reaction 
are usually far in excess of the amount which ever 
appears in non typhoid blood, so that the reaction 
occurs after the addition to the culture of far smaller 
quantities of serum than in other diseases, or when the 
same dilution is used it occurs far more quickly and 
completely with the typhoid serum. 
