416 BACTERIOLOGY. 
immunized has been found to acquire protective and 
curative bactericidal and perhaps feeble antitoxic prop- 
erties against the typhoid bacillus. These character- 
istics have also been observed in the blood-serum of 
persons who are convalescent from typhoid fever 
(Pfeiffer and Kolle, Widal and Chantemesse). Re- 
cently the attempt has been made to employ the 
typhoid-serum for the cure of typhoid fever in man, 
but no marked results have been obtained. The injec- 
tion in man of very small amounts (0.3 c.c. of bouillon 
culture) of dead typhoid bacilli produces for a day or 
two a slight fever reaction, to be followed in a few days 
by the development of bactericidal substances in the 
blood, which apparently are sufficient in amount to 
give immunity for some weeks. The use of immu- 
nized serum, or when this cannot be obtained of dead 
cultures, would seem to be advisable where great 
danger of typhoid infection exists. 
The Diagnosis of Typhoid Fever, or rather of Typhoid 
Infection, by Means of the Widal or Serum Reaction. 
The chief practical application of our knowledge of the 
specific substances developed in the blood of persons 
sick with typhoid fever has been in the way of 
diagnosis. In view of the interest which has been 
manifested in this test, and of the fact that it is now 
so largely used, a brief history of the investigations 
which led up to its discovery may be given. ~ 
In 1894-95, Pfeiffer showed that when cultures con- 
taining dead or living cholera spirilla or typhoid bacilli 
are injected subcutaneously into animals or man, specific 
protective substances are formed in the blood of the in- 
dividuals thus treated. These substances grant a more 
or less complete immunity against the invasion of the 
