388 TYPHOID FEVER 



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. If the organism be grown for two or three weeks in 

 an alkaline bouillon, there appears, probably by autolysis of the 

 bacteria, a toxin in the culture medium separable by nitration in 

 the ordinary way. The optimum alkalinity is achieved by 

 adding '3 per cent, of soda to bouillon neutral to litmus, the 

 resulting precipitate not being removed ; free access of oxygen 

 is permitted during growth. Apparently, the Shiga-Kruse 

 strains yield the most toxic nitrates, and with the Flexner 

 strain, the results of most observers show that soluble toxins 

 cannot be obtained. The poison is very toxic to animals, 

 especially rabbits, and however introduced into the body it 

 causes after an incubation period haemorrhagic enteritis with a 

 diphtheritic-like exudate on the surface of the mucous membrane. 

 Toxins isolated from different strains differ as regards the 

 animals for which they are most toxic. The toxin is fairly 

 resistant to heat, standing temperatures up to 70 C. without 

 being injured. 



It may be said that an aggressive reaction (vide p. 189) has 

 also been described in the case of the dysentery bacillus. 



Immunisation Experiments. Both large and small animals 

 have been immunised against the bacillus and also against its 

 toxic nitrates. 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 

 immunisation, a serum protecting against the toxin is produced. 

 According to some results, animals immunised with cultures are 

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

 do not lend themselves to immunisation. 



Considerable work has been done in immunising large 

 animals (horses, goats) against the soluble toxins of the 

 dysentery bacillus with a view to obtaining therapeutic sera. 

 Doerr, using his toxin from the Shiga-Kruse strain, produced 

 in horses an antitoxic serum having protective and curative 

 properties in animals. This serum has been used in a number 

 of cases of bacillary dysentery in man with good results. Shiga 



