444 PATHOGENIC MICROORGANISMS 



diarrhea. This is at first watery, later contains large amounts of blood. 

 If the animals live a sufficient length of time, paralysis may occur, the 

 animal may fall to one side or may drag its posterior extremities. It is 

 a remarkable fact that intravenous inoculation gives rise to intestinal 

 inflammation of a severe nature, unquestionably due to the excretion 

 of the poison by the intestinal mucosa and limited, usually, to the ce- 

 cum and colon, rarely attacking the small intestine. Flexner,' who has 

 experimented extensively upon this question, beheves it probable that 

 most of the pathological lesions occurring in the intestinal canal of dysen- 

 tery patients are referable to this excretion of dysentery toxin, rather 

 than to the direct local action of the bacilli. 



Toxins from the Shiga-Kruse type are the most potent and those 

 which cause paralysis. 



Immunization with Dysentery Bacilli. — ^The immunization of small 

 animals, such as rabbits and guinea-pigs, against dysentery bacilli, 

 especially those of the Shiga type, is attended with much difficulty, 

 owing to the great toxicity of the cultures. Nevertheless, successful 

 results may be accomplished by the administration of extremely small 

 doses of living or dead bacilli, increased very gradually and at sufficient 

 intervals. Horses may be more easily immunized. The serum of such 

 actively immunized animals contains agglutinins in considerable con- 

 centration and of a specificity sufficiently illustrated in the preceding 

 section dealing with the identification of the various species. For 

 diagnostic purposes in human beings, the agglutination reaction, accord- 

 ing to the technique of the Widal reaction for typhoid fever, has been 

 utilized by Kruse ^ and others. According to most observers, normal 

 human serum never agglutinates dysentery bacilli in dilutions greater 

 than one in twenty, while the serum of dysentery patients will often be 

 active in dilutions as high as one in fifty. 



Bactericidal substances have been demonstrated in the serum of im- 

 munized animals as well as in the serum of diseased human beings. 

 These have been determined, in vitro, by Shiga,^ and by the intraperito- 

 neal technique of Pfeiffer by Kruse. ^ Bacteriolysis may take place in 

 high dilutions of the serum, and has recently been used for the differen- 

 tiation of the types of the dysentery bacilli by Ohno.^ 



True antitoxins in immune sera have been recently described by 

 Kraus and Doerr." 



' Flexner, Jour. Exp. Med., 8, 1906. 2 Kruse, Deut. med. Woch., 1901, 



3 Shiga, Zeit. f. Hyg., xli. * Kruse; Deut. med. Woch., 1903. 



5 Ohno, Philippine Jour, of Sci., vol. i, 1906. ' KroMS tind Doerr, loc. cit. 



