THE COLON-TYPHOID GROUP 109 



Culture. The bacilli are aerobic and facultatively 

 anaerobic. The growths on surface agar and gelatin 

 are much like those of typhoid; there is no liquefaction of 

 gelatin. In broth and peptone-water there is a general 

 turbidity without pellicle; indole may or may not be 

 formed. On potato the growth is usually thin and colour- 

 less, sometimes yellowish or brownish. In milk it grows 

 well without clotting, the reaction being first acid, and 

 generally after a few days becoming alkaline. It ferments 

 glucose with the production of acid, but no gas; lactose 

 is not attacked, and neutral red is unchanged. 



The varieties are identified by agglutination reactions 

 and action on mannitol. The Flexner type ferments 

 mannitol with production of acid, but no gas, while the 

 Shiga-Kruse bacillus has no action on this polyhydric 

 alcohol. Some varieties ferment maltose and saccharose 

 as well. 



The thermal death-point is about 60 C. Soluble 

 thermostable toxins are formed in alkaline media, and 

 Todd has been able to produce an antitoxin by treating 

 an animal with the toxin. 



Agglutinating Reaction. Provided the type of organ- 

 ism causing the disease be employed, the blood-serum of 

 patients with bacillary dysentery gives an agglutination 

 reaction, sometimes in high dilutions. Whereas agglutina- 

 tion can be obtained on the second day in some cases, in 

 others it is not found till the twelfth day. 



Pathogenesis. The liver abscesses generally found in 

 amoebic dysentery do not occur in the bacillary disease, 

 and the organism is not found in the urine or blood, but 

 it is abundant in the bowel discharges. The incubation 

 period, after the bacilli have been swallowed, is from one 

 to two days. 



The organism is met with in the so-called ulcerative 

 colitis, or ' asylums dysentery,' and in a considerable 

 proportion of cases of epidemic (summer) diarrhoea of 

 infants. 



Direct or indirect contact with infected bowel dis- 

 charges is recognised as a principal means of infection. 

 After apparent recovery the convalescent may still 

 excrete the bacilli. Polluted water has been held re- 

 sponsible for infection, but Forster has shown that the 

 Shiga bacillus has but a short life outside the body, and 



