MICROBIAL DISEASES QF MAN AND DOMESTIC ANIMALS 847 



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

 reaction should be distinct in about one hour. 



Owing to the extensive adoption of inoculation against typhoid and 

 paratyphoid fevers, the problem of exact diagnosis has become more 

 difficult. If culture fails to reveal the exciting organism it becomes 

 necessary to take a series of at least three agglutination tests at inter- 

 vals of two or three days in order to determine the comparative curves 

 of agglutinin for B. typhosus, B. paratyphosus A. and B. paratyphosus B. 

 For this purpose Dreyer's technique has been largely used. 



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 

 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 5 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 100 to 500 

 c.c. amounts, which 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 media have been devised, some depending on the motility 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 bacillus is about i/x to 3.5/1 in length and 0.5^ to 

 o.S/z in width (Fig. 178). Filaments are sometimes found several times the length 

 of the single organism. It is quite regular in shape, straight with rounded ends. 

 The bacilli usually occur singly; occasionally two may be attached end to end for a 

 short time. There are ten to fourteen comparatively stout flagella about two or 



