132 THE ACUTE SELF-LIMITED INFECTIONS 



in immunizing the lower animals with toxins obtained 

 in laboratory cultures. As an aid in the diagnosis of 

 dysentery the stools in which the bacteria may be found 

 almost in pure culture are cultivated. The shreds of 

 membrane or mucus from the stools are selected. 

 The development in the laboratory is comparatively 

 simple, but to identify the species or variety is any- 

 thing but easy. The agglutinins in the patient's 

 blood may be tested against pure laboratory cultures 

 of known varieties, and thus a bacteriological diagnosis 

 as to the type may be made. Thus for diagnosticating 

 dysentery we have only the feces culture and agglutin- 

 ation test. Since the bacilli are not in the blood, 

 cultures of this are not made. 



The dysentery bacillus is a short, straight, probably 

 non-motile rod with rounded ends. It is quite like 

 the typhoid bacillus in shape and size, but unlike this 

 germ does not move actively. It may at times show 

 degenerated forms. It is usually single, but may be 

 in pairs. It stains easily. It grows both aerobically 

 and anaerobically, but better under the former con- 

 ditions. Its growth upon laboratory media is also 

 like that of the typhoid bacillus. Best development 

 occurs at 37 C. or 98 F., and death results when 60 C. 

 or 142 F. is held for ten minutes. 



It resists freezing for a long time, possibly some 

 weeks. It is killed by drying only after long periods. 

 Its resistance to chemicals is practically the same 

 as that of typhoid bacilli. Animals do not contract 

 dysentery when they take the bacilli by mouth, but 

 when germs or their toxins are introduced under the 

 skin, into the vein or peritoneum, profound intoxica- 



