MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 817 



be used for isolation, but ordinary litmus lactose agar plates are satis- 

 factory for Shiga and "Y" types. 



Bact. dysenteries (Shiga) is rather short with rounded ends and closely 

 resembles the typhoid bacillus morphologically except that it does not 

 possess flagella. 



It stains readily with the aniline dyes and is Gram-negative. It grows best at body 

 temperature, is aerobic and facultatively anaerobic. It prefers a slightly alkaline 

 medium. On agar, broth, and gelatin growth resembles that of the typhoid bacillus. 

 In litmus milk an alkaline reaction usually follows a slight primary acidity without 

 any further apparent change. On potato growth it is at first invisible but may appear 

 later of a brownish color. Acid is formed from dextrose, levulose, and galactose. 

 (Other types described differ from this in the fermentation of mannit and sometimes 

 of maltose.) Gas is never formed. Indol is not formed. (Other types usually form 

 indol.) The toxins are probably chiefly endotoxins, though soluble poisons have also 

 been demonstrated by some workers. The bacterium remains alive for months when 

 preserved under the proper conditions. The thermal death point is 60 and re- 

 sistance to low temperature is considerable. It is sensitive to the usual strength of 

 ordinary disinfectants. 



Dysentery does not occur in animals under natural conditions. By 

 artificial methods, however, it is claimed the disease has been repro- 

 duced in dogs. Cultures, living or dead, are often extremely toxic to 

 small animals, especially the rabbit, and produce, after intravenous 

 injection, violent intestinal symptoms, due evidently to the excretion 

 of an irritating poison. Nervous symptoms are also more or less 

 marked and paralysis sometimes occurs before death. Immunity pro- 

 duced artificially in animals is accompanied by the production of lysins 

 and agglutinins and lately antitoxins have been described in accord 

 with the demonstration of diffusible toxins. The agglutination in man 

 is of diagnostic value. 



The epidemiology of dysentery is the same as for typhoid fever. In 

 a few instances the bacilli have been demonstrated in the faeces of 

 healthy persons, and convalescents may remain carriers for several 

 months. 



Some success has been recorded from the administration of animal 

 immune sera and has been attributed to both lytic and antitoxic 

 action. Active immunization as a means of prophylaxis does not seem 

 to be of much value. 



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