BACILLI OF THE COLON-TYPHOlB-DYSENTERY GROUP 663 



small test tubes. In all cases it is desirable first to determine the 

 agglutinating power of the scrum when tested against a known 

 typhoid culture. (For detailed technique, see chapter on Technique 

 of Serum Reactions, page 302, 282.) 



In scientific investigations, specific agglutinations in high dilutions 

 of immune serum constitute very strong proof of the species of the micro- 

 organism and may often furnish much information as to the biological 

 relationships between similar species. It is found in immunizing ani- 

 mals with any given strain of typhoid bacilli, that there are formed 

 the " chief" or " major" agglutinins which are specific and active 

 against the species used in immunization, and the "-group" or "minor" 

 agglutinins, active also against closely related microorganisms. The 

 following extract from a table will serve to illustrate this point in the 

 case of typhoid and allied bacilli. 



The sera of most adult normal animals and human beings usually 

 contain a small amount of agglutinin for these bacilli. Immunization 

 with the typhoid bacillus, while increasing chiefly the agglutinin 

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

 agglutinins 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 288.) 



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

 tination was first utilized by Widal. 64 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 



64 Widal, Bull, de la soc. mcd. des hopit., vi, 1896; Widal et Sicard, Ann. de 

 1'inst. Pasteur, xi, 1897. 



