QUALITATIVE BACTERIOLOGICAL ANALYSIS. 151 



masses of bacteria gradually sink to the foot of the liquefied 

 medium. 



Gelatine-shake. No gas is formed. Sometimes the colonies 

 have a star-shaped appearance, but at other times they are 

 globular. 



Broth. At 37 C. there is a diffuse cloudiness ; later a skin 

 forms on the surface, and an abundant white deposit forms at 

 the foot of the tube, leaving the liquid above fairly clear. 



Indol. No indol is formed in broth cultures. 



Litmus -mill:. No decided change after seventy-two hours at 

 37 C. In five days weak gelatinous clot, but no acidity. 



Potato. By the second day at 37 C. a fairly abundant 

 creamy coating has formed on the surface, and later becomes 

 of a dirty-brown colour. 



Nitrate-broth. Reduces nitrates to nitrites. 



Microscopical Appearances, fyc. A large bacillus forming 

 long chains. It is motile. Old cultures resist heating to 80 C.; 

 but a satisfactory preparation of spores has not been obtained. 

 It grows luxuriantly at 37 C. and at room temperature. 



Bacillus Mesentericus (Sewage variety E.). 



Isolated from London crude sewage. Gelatine plates heated 

 to 80 C. for ten minutes. 



Gelatine-plate Cultures. The growth is not very rapid. The 

 deep colonies have a somewhat star-like appearance ; the super- 

 ficial colonies appear as bluish-white, delicate granular films, 

 which are almost colon-like in character. They are somewhat 

 irregular in shape, and from the wavy transparent edge 

 irregular processes are given off'. Under a low power the deep 

 colonies show a central darkish yellow spot from which root-like 

 processes are given off'. The surface colonies are transparent, 

 granular, and striated ; and from the edge delicate processes are 

 given off', which spread over the gelatine, forming curious and 

 intricate patterns. The colonies do not attain a large size, 

 and liquefaction only slowly sets in. 



Gelatine-stab. The growth at the surface is slow and resembles 

 a superficial colony. Growth takes place all the Avay down the 

 stab accompanied by slow liquefaction; delicate tuft-like fila- 

 ments are given off' all down the line of inoculation. 



