BACILLUS OF TYPHOID FEVER 421 



for this bacillus itself, also to a slighter extent increases the group ag- 

 glutinins for other closely allied species. That these group agglutinins 

 are separate substances and not merely a weaker manifestation of the 

 action of the typhoid agglutinin itself upon these other microorganisms, 

 may be demonstrated by the experiments of agglutinin absorption. 

 (See section on Agglutinins, page 234.) 



Immune serum obtained by immunization with one particular ty- 

 phoid culture usually agglutinates this culture in higher dilutions than 

 it will agglutinate other typhoid strains. This has been noticed in a 

 large number of investigations, but is not always the case. 



In the clinical diagnosis of typhoid fever, the phenomenon of agglu- 

 tination was first utihzed by Widal.' This observer called attention to 

 the fact that during the last part of the first or the earlier days of the 

 second week of typhoid fever, as well as later in the disease and in con- 

 valescence, the blood serum of patients would cause agglutination of 

 typhoid bacilli in dilutions of 1 : 10, or over, whereas the serum of 

 normal individuals usually exerted no such influence. Upon this basis 

 he recommended, for the diagnosis of the disease, the employment of a 

 microscopic agglutination test carried out by the usual hanging-drop 

 technique. The reaction of Widal is, at present, widely depended upon 

 for diagnostic purposes and although not universally successful, owing 

 to irregularities in agglutinin formation in some patients, and because of 

 differences in agglutinability of the cultures employed, it is nevertheless 

 of much value. The original conclusions as to the dilutions of the 

 serum which must be employed, have, however, necessarily been modi- 

 fied. Owing to the fact that Gruber,^ Stern,' Frankel,'' and a number of 

 others have found that occasionally normal serum will give rise to ag- 

 glutination of typhoid bacilli in dilutions exceeding 1 : 10, it has been 

 found necessary, whenever making a diagnostic test, to make several 

 dilutions, the ones most commonly employed being 1 : 20, 1 : 40, 1 : 60, 

 and 1 : 80. The wide application of the method has given rise to the 

 development of a immber of technical procedures, all of them devised 

 with a view toward simplification. In ordinary hospital work, it is most 

 convenient to keep on hand upon slant agar, a stock typhoid culture, the 

 agglutinability of which is well known. From this stock culture, fresh 



' Widal, Bull, de la soc. m6d. des hdpit., vi, 1896; Widal et Sicard, Ann. de 

 I'inst. Pasteur, xi, 1897. 



'Gruber, Verhand. Congr. f. inn. Med., Wiesbaden, 1896. 

 'Stern, Cent. f. inn. Med., xlix, 1896. 

 'Frankel, Dent. med. Woch., ii, 1897. 



