420 



PATHOGENIC MICROORGANISMS 



are cultivated in immune 8erum. A similar alteration in the agglutin- 

 ability of typhoid bacilli was noted by Eisenberg and Yolk * when they 

 subjected the microorganism to moderate heat or to weak acids such as 

 J HC1. 



The practical application of agglutination to bacteriological work is 

 found, as in the case of the bactericidal substances, in the identification 

 of suspected typhoid bacilli, and in the diagnosis o'f typhoid fever. 



When it is desired to determine by means of agglutination whether 

 or not a given bacillus is a typhoid bacillus, mixtures may be made 

 of young broth cultures, or preferably of emulsions of young agar cul- 

 tures in salt solution, with dilutions of immune serum. The tests are 

 made microscopically in the hanging-drop preparation or, preferably, 

 macroscopically in small test tubes. In all cases it is desirable first to 

 determine the agglutinating power of the serum when tested against 

 a known typhoid culture. (For detailed technique, see chapter on 

 Technique of Serum Reactions, p. 250.) 



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. Immuniza- 

 tion with the typhoid bacillus, while increasing chiefly the agglutinin 



1 Eisenberg und Volk, Zeit. f. Hyg., xlv, 1903. 



