284 VETERINARY BACTERIOLOGY 



typhoid bacillus, it does not commonly invade the blood or the 

 internal organs, with the exception of the mesenteric glands. 

 The disease is rather a toxemia than a bacteremia. 



Immunity. A soluble toxin has been demonstrated for the 

 Shiga type, but repeated efforts have failed to show that any such 

 is produced by the Flexner type. This poison was at first believed 

 to be an unusually potent endotoxin. Conradi first demonstrated 

 the toxin by growing the organism upon agar, then suspending it in 

 physiologic salt solution, and allowing the bacteria to undergo 

 autolysis. Later, Rosenthal and others showed that toxin will 

 be produced in considerable quantities in an alkaline bouillon, 

 but not in one that is neutral or acid. This bouillon is either 

 filtered through porcelain filters, or 0.5 per cent, phenol is added 

 and allowed to stand, and then filtered through paper until clear. 

 The toxin may be precipitated by ammonium sulphate, and after 

 dialysis and drying of such, 1 to 2 gm. may be a lethal dose for a 

 kilo of rabbit. It is weakened by prolonged heating at 70, 

 and destroyed at 80 to 100. The rabbit is very susceptible to 

 the injection of the toxin, while the guinea-pig is relatively resist- 

 ant. The effect upon the rabbit may be characterized as a hemor- 

 rhagic necrotic enteritis. 



Shiga first used antisera in the treatment of dysentery. He 

 regarded its curative properties as wholly bactericidal. Todd, 

 Koram, Doerr, and others have, by systematic immunization of a 

 horse, secured a serum that neutralizes the toxin actively. This 

 has been used with very favorable results in the treatment of dys- 

 entery caused by the Shiga bacillus. 



Bacteriologic Diagnosis. The disease may be recognized by 

 the Widal or agglutination test, and the several types of organisms 

 differentiated in the same manner. The organism may likewise 

 be isolated directly from the stools by plating. 



Transmission. Dysentery is spread irt much the same manner 

 as typhoid, and the same preventive measures must be used. 



BACTERIA OF WATER AND WATER PURIFICATION 



Diseases of man and animals, particularly those of the alimen- 

 tary tract, are frequently transmitted through contaminated or 

 impure water. The impurity, so called, arises from the presence 



