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 



