614 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



criminal fed with a pure culture of Shiga's organism developed the typica 

 disease. 



The organism can occasionally be isolated in almost pure culture from 

 bits of mucus in the stool. Ordinarily, however, special methods are 

 required for isolation. 



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

 the typhoid bacillus in gross morphological features. 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 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 resistance 

 to low temperature is considerable. They are sensitive to the usual strength of 

 ordinary disinfectants. 



Dysentery does not occur in animals under natural conditions. By 

 artificial method, however, it is claimed the disease has been reproduced 

 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 produced artificially in ani- 

 mals 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 fasces 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. 



