794 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



patients, after a certain period of the disease, will cause a characteristic 

 clumping of the baciUi when mixed with pure cultures. The fresh 

 serum from a clot may be used, or, more conveniently, dried blood 

 from which a watery extract can be made. In positive cases the reac- 

 tion is present in at least the one-fiftieth dilution and usually in the one- 

 hundredth or higher dilutions. The culture employed should be 

 eighteen to twenty-four hours old; it should be freely agglutinable and 

 show no artificial clumping, characters not possessed by all strains, 

 especially those recently isolated. Cultures kiUed by a small per- 

 centage of carbolic acid have been recommended for constancy in place 

 of the living organisms. When the microscopic method is used the 

 reaction should be distinct in about one hour. 



An immune body capable of binding complement in the presence 

 of typhoid antigen is said to occur in typhoid sera before the agglutina- 

 tive property appears. < 



The detection of the typhoid bacillus in the circulating blood has 

 recently been very widely successful and furnishes the best support for 

 the diagnosis of the disease. While blood culture may be hardly 

 practical in public health laboratories, it has become a routine measure 

 in the modern hospital. Blood is taken aseptically from a vein and 

 about I to s c.c. is introduced into culture media, of which fluid media 

 containing ox-bile and agar plating media containing glucose have been 

 most strongly recommended. The fluid media, are used in loo to 500 

 c.c. amounts, wliich serves to dilute the antibacterial properties of the 

 blood while the bile acts as an anticoagulant and possibly also as an~ 

 antibactericidal measure. Plating lessens the diffusion of the anti- 

 bacterial properties and thus favors growth. 



The urine and faeces have sometimes to be examined for the presence 

 of B. typhosus. It then becomes necessary to differentiate the colonies 

 of this bacillus from those of the colon group. For this purpose many 

 special medid, have been devised, some depending on the motihty of the 

 typhoid bacillus to form a different shaped colony in suitable soft 

 media, others based on the fact that some substances such as fuchsin, 

 crystal violet, malachite green, etc., inhibit the growth of associated 

 organisms while permitting the typhoid bacillus to develop more or less 

 luxuriantly. 



As found in pure cultures, the bacUIus is about i/i to 3.5/^ in length and 0.5^1 to 

 0.8m in width (Fig. 167). Filaments are sometimes found several times the length 



