436 PATHOGENIC MICROORGANISMS 



morphologically very similar to the typhoid bacillus, and, like it, 

 inclined to involution forms. The organism generally occurs 

 singly, more seldom in pairs. It is decolorized by Gram's 

 method of staining. With the ordinary anilin dyes it stains easily, 

 showing a tendency to stain with slightly greater intensity at 

 the ends. The organism is an aerobe and facultative anaerobe. 

 Although described at first by Shiga as being motile, its motility 

 has not been satisfactorily proven, and most observers agree in 

 denying the presence of flageUa and affirming the complete absence 

 of motility. 



Cultural Characteristics. — On agar the colonies are not characteristic, 

 resembling those of the typhoid bacillus. 



On gelatin, the colonies appear very much like typhoid colonies and 

 the gelatin is not liquefied. 



On potato, the growth, like that of typhoid, is at first not visible, but 

 after about a week turns reddish brown. 



In broth, there is clouding, with moderate deposits after some days. 

 No pellicle is formed. 



Milk is not coagulated. Litmus milk shows a slight primary acidity, 

 later again becoming alkaline and taking on a progressively deeper blue 

 color. 



Indol is not formed in pepton water by all varieties. 



No gas is formed in media containing dextrose, lactose, saccharose, 

 or other carbohydrate. 



While not delicately susceptible to reaction, the bacillus prefers 

 slightly alkaline media. 



Shiga differentiated his organism from the typhoid bacUlus chiefly 

 by supposed differences in colony characters and by the agglutination 

 reaction. 



Following the work of Shiga, a large number of investigators turned 

 their attention to the subject of dysentery, with the result that many 

 new forms were discovered and at first a considerable amount of con- 

 fusion prevailed. 



Flexner ' in 1899 investigated dysentery in the Philippines, and 

 isolated a bacillus which, he considered, corresponded to Shiga's 

 organism. 



Strong and Musgrave ' in 1900 described a bacillus isolated from 



> Flexner, Phila. Med. Jour., vi, 1900, and Bull. Johns Hopkins Hosp., xi, 1900. 

 ' Strong and Musgrave, Report Surg. Gen. of Army, Washington, 1900. 



