642 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



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 antibacteri- 

 cidal measure. Plating lessens the diffusion of the antibacterial proper- 

 ties and thus favors growth. 



The urine and fseces 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 



^ 



V 



' . w x 



FIG. 112. Bacillus of typhoid fever. Xiooo. (After Williams.) 



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/j. to 3.5^ in length and .5/1 to .8/t 

 in width (Fig. 112). 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 fora short 

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

 the length of the organism peritrichic in their arrangement. There are no capsules 

 and no spores. They stain with all aniline dyes, and not infrequently exhibit more 

 deeply staining areas at the poles. They are Gram-negative. Biological and Bio- 



