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 agglu- 

 tinins are separate substances and not merely a weaker manifestation 

 of the action of the typhoid agglutinin itself upon these other micro- 

 organisms, may be demonstrated by the experiments of agglutinin 

 absorption. (See section on Agglutinins, page 234.) 



In the clinical diagnosis of typhoid fever, the phenomenon of 

 agglutination was first utilized by Widal. 1 This observer called at- 

 tention 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 dis- 

 ease and in convalescence, 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 uni- 

 versally 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 fact that 

 the recent work of Hooker and of Weiss has shown that typhoid bacilli 

 differ in antigenic properties, and may on the basis of agglutination 

 and agglutinine absorption be divided into a number of groups, will 

 necessitate the use of several cultures for Widal reactions. The orig- 

 inal conclusions as to the dilutions of the serum which must be em- 

 ployed, have, however, necessarily been modified. Owing to the; fact 

 that Gruber, 2 Stern, 3 Frankel, 4 and a number of others have found that 

 occasionally normal serum will give rise to agglutination of typhoid 

 bacilli in dilutions exceeding 1 : 10, it has been found necessary, when- 

 ever 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, 

 number of technical procedures, all of them devised with a view 

 toward simplification. In ordinary hospital work, it is most con- 

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

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



1 Widal, Bull, de la soc. meU des hopit., vi, 1896; Widal et Sicard, Ann. de 

 Pinst. Pasteur, xi, 1897. 



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



9 Stern, Gent. f. inn. Med., xlix, 1896. ! *Frankel, Deut. med. Woch., ii, 1897, 



