120 MEDICAL BACTERIOLOGY 



They cannot be found in feces 48 hours after defecation, due to the an- 

 tagonistic action of the colon bacillus. In water saprophytic bacteria cause 

 them to disappear in a few days. They dry out in cultures after 3 or 4 weeks, 

 unless transplanted. In a moist state 55C. kills them in less than an hour. 

 In a hot-air sterilizer they are destroyed in less than an hour at iooC. 



Toxin. Dysentery bacilli form an intracellular toxin. 



Agglutinins, precipitins and amboceptors occur in the serum of dysentery 

 patients and immunized animals. The agglutinins are specific; the serum from 

 a patient agglutinates the type of bacillus causing his condition, but none of 

 the other dysentery bacilli. The amboceptors give a group reaction; they will 

 fix complement when any type of dysentery bacillus is used as antigen. 



Pathogenesis Bacillary dysentery results from ingestion of polluted water 

 or food. The bacteria are usually confined in the primary seat of infection 

 the intestines it is possible that in some cases they may migrate to the gall- 

 bladder, but there is not a bacteremia as in typhoid fever. They escape in the 

 feces and bloody mu'cous flux of the disease. Bacteria are most readily found 

 in the stools during the first days of the disease and disappear after several 

 weeks. 



Different types of dysentery bacilli show different degrees of virulence, and 

 it is said that the Shiga type is the most virulent. 



Relatively large amounts of living bouillon cultures introduced through the 

 esophagus produce signs and lesions of the disease in guinea-pigs and rabbits 

 similar to the manifestations observed in man. 



Diagnosis. The bacteriological diagnosis of dysentery consists in the 

 examination of feces microscopically and by culture and examination of blood 

 serum for agglutinins. 



Feces. Have the patient defecate into a sterile bed pan, immediately pick 

 out a mucous shred and place it on a slide and let a cover glass fall upon it; 

 then, examine under the microscope for ameba. When ameba are present 

 they may not be found until a number of slides have been examined. If several 

 slides made from mucus fail to show them, slides should be made from the fluid 

 portion of the feces and from solid particles by dipping a camel's-hair brush 

 into it and gently smearing the slide. 



After making a microscopic examination for ameba, or before doing so, 

 a shred of the gelatinous-like substance or blood matter found in such stools is 

 sought for, removed with a platinum loop, washed with sterile water and then 

 drawn across the surface of a number of plates of Endo's agar. The plates are 

 incubated at 37C. for 18 to 24 hours. Red colonies are passed by; any color- 

 less colonies that appear are removed and transplanted into litmus milk, 

 Dunham's solution, and litmus bouillon, containing various carbohydrates, 

 used to differentiate dysentery bacilli. The subcultures are incubated at 

 37C. and inspected each day for several days. If a dysentery bacillus is found, 

 a 24-hour-old bouillon culture is used to make agglutination tests with the 

 patient's serum. 



Agglutination Tests. The patient's finger is asepticized, pricked with a 



