BACTERIDS. 127 



In Gelatine. — Within twenty-four hours this rapidly growing organ- 

 ism has produced a dimple-like depression in the surface of the 

 gelatine at the point of inoculation. This shortly afterwards becomes 

 a funnel-shaped cavity filled with a turbid liquid, in which a faint 

 tinge of opalescent green is evident. By the third or fourth day the 

 upper strata of the jelly are liquefied, and the liquid possesses a bright 

 iridescent green colour (Fig. 44, p. 87). Within a week or ten days the 

 whole of the nutrient jelly has liquefied, and the green gradually gives 

 place to a deep citron colour in the liquid. Grown in jelly, B. termo 

 produces little or no odour. 



In Liquid Media. — B. termo produces a dense turbidity, equally 

 disseminated throughout the liquid. Its growth is accompanied by 

 a very penetrating putrescent odour. 



Microscopically. — In its freely moving form B. termo appears as a 

 small dumb-bell, about 1 /x. long and 0-5 jx. broad. Long flagella 

 attached to each end have been described by Dallinger. The organ- 

 isms have an irregular flickering movement, appearing to rotate on 

 their own long axes, and gliding alternately in either direction, 

 usually in straight lines, but at times describing curves or looped 

 figures in their onward progress. 



In its zooglea form the bacterium appears as short straight rods, 

 clustered together in a clear transparent jelly-like mass, many of the 

 organisms undergoing division by transverse fission. In this stage the 

 organism lies quiescent, and the flagella are absent. The zooglea mass 

 often forms an iridescent scum on the surface of decomposing liquids. 



Bacterium lineola. On potato this organism forms a film identical 

 in appearance with that produced by B. termo, but tending to grow 

 rather more rapidly and luxuriantly. In jelly and in liquid media, 

 there are precisely similar reactions to those produced by the presence 

 of Termo. It is only by its microscopic characters that B. lineola 

 can be differentiated. In its freely moving form it is elliptical in 

 shape and about 5 /a. long by 2 /x. broad ; it also has two flagella, one 

 at either end, and moves in the same manner as B. termo. With this 

 form alternates a zooglea form, where great numbers of immobile 

 organisms are aggregated together within a delicate jelly-like mass. 

 This organism is found in all putrefying animal matter, and is one of 

 those associated with putrescent odours. 



Bacterium lactis. — In milk, produces the characteristic odour 

 and taste of sour milk, but does not cause coagulation, as many 

 micro-organisms do. 



Microscopically. — It consists of small dumb-bells, 2 \i. x 1 //,., which 

 have very active movements. Here and there they are found aggre- 

 gated into clusters, which seem to represent the zooglea stage of this 

 organism. 



Bacterium xanthinum. — Grows in boiled milk, producing a slight 

 yellow colour. A small bacterium, apparently identical morphogically 

 with B. termo. 



