BACILLUS DYSENTERIC 349 



will yield a serum which is active against many more strains 

 than other species will when immunised with that strain. 

 Agglutination of the organism has not been obtained with serum 

 from cases other than those of dysentery, nor has a similar bacillus 

 been cultivated from other such sources. The reaction is also 

 absent in those cases of dysentery which are manifestly of amoebic 

 nature. 



Pathogenic Properties. The organism is pathogenic in guinea- 

 pigs and other laboratory animals, but, in these, characteristic 

 changes in the intestine are often awanting. Shiga, however, 

 obtained such effects by introducing the organism into the 

 stomach of young cats and dogs, and confirmatory results were 

 obtained by Flexner. Such attempts have been specially 

 successful when the virulence of the organism has been previously 

 exalted by intraperitoneal passage. In two cases, apparently 

 well authenticated, a dysenteric condition has followed in the 

 human subject from ingestion of pure cultures of the organism. 



It is probable that in the action of the bacillus a toxin is 

 concerned. It has been found that the nitrate from three weeks' 

 old cultures in alkaline bouillon is very toxic to animals, especially 

 rabbits, and that, however introduced into the body, it causes 

 a haBmorrhagic enteritis with a diphtheritic-like exudate on 

 the surface of the mucous membrane. According to some obser- 

 vers the toxin is more readily obtainable from the Shiga-Kruse 

 strains than from the Flexner strains. The toxin is fairly resist- 

 ant to heat, standing temperatures up to 70 C. without being 

 injured. From the fact, that by the maceration of cultures 

 whose filtrates are relatively non-toxic a stronger poison can be 

 obtained, the dysentery toxin has been thought to be an 

 endotoxin, but on this point no definite opinion can be expressed. 



Immunisation Experiments. Both large and small animals 

 have been immunised against the bacillus and also against its 

 toxic filtrates. In the former case the immunisation has been 

 commenced either with non-lethal doses of living cultures or with 

 cultures killed by heat. The nature of the immunisation is 

 probably complex. When cultures have been used, a bactericidal 

 serum, in which immune bodies and complements (vide Immunity) 

 are concerned, is developed. When the toxin is used for immun- 

 isation a serum protecting against the toxin is produced. Ac- 

 cording to some results animals immunised with cultures are 

 immune against the toxin, and vice versa. All races of animal 

 do not lend themselves to immunisation. Large animals (horses, 

 goats) have been immunised with the toxin with a view of ob- 

 taining sera for use in human dysentery, and in certain cases, 



