164 BACTERIOLOGICAL EXAMINATION OF WATER. 



Litmus-whey. After seven days incubation at 37 C. there is 

 a slight development of acid, which, however, never requires 



more than 6 per cent, of ^ alkali to neutralise it. 



Broth. A diffused growth takes place; an imperfect film 

 appears on the surface after several days incubation. 



Gelatine (25 per cent.). After incubation at 37 C. no film 

 appears on the surface, but a diffused growth takes place 

 throughout the medium. 



Proskauer and Capaldi's Medium, No. I. (Asparagin and 

 Salts). After twenty-four hours incubation at 37 C. there is 

 no growth. 



Proskauer and Capaldi's Medium., No. II. (Witters Peptone 

 and Mannite). After twenty-four hours incubation at 37 C. 

 there is a distinct growth, and the medium acquires a strongly 

 acid reaction. 



Microscopical Characters. A bacillus about 3 /u long and 

 1 ni broad, highly motile, with a quick, serpentine move- 

 ment. 



Staining Reactions. Stains readily with basic dyes. It is 

 decolorised by Gram's method. 



Flagella. Eight to twelve long wavy flagella, disposed all 

 round the bacillus. 



Spore-formation. It does not form spores, and is destroyed 

 when the cultures are heated to a temperature of 65 C. for ten 

 minutes. 



Reactions with Anti-typhoid Serum. The B. typhosus is quickly 

 agglutinated by a highly dilute anti-typhoid serum. A small 

 dose of anti-typhoid serum injected into the peritoneum of a 

 guinea-pig, along with a lethal dose of B. typhosus, protects the 

 animal from the effects of this organism. 



The most important of the above tests are the following : 



(1) The Slow Growth on Gelatine Plates. This test is of great 

 value ; none of the varieties of B. coli grow so slowly on gela- 

 tine plates as the B. typhosus. The B. enteritidis of Gartner, 

 and the organisms of the so-called Gartner group, are the only 

 bacilli which really grow like B. typhosus on gelatine plates, 

 though even these appear to grow more quickly than the true 

 typhoid organisms. 



