of the Type of De Bary's B. megatherium. 341 



material, and the degree of condensation of the medium. Thus if a 

 gelatine culture becomes liquefied, either by the normal liquefying 

 action of the bacillus itself, or by the addition of water, the sheath 

 gradually dissolves, and the colonies disintegrate into flocculent masses 

 of rods possessing only very thin sheaths. In liquid cultures the 

 rods are practically non-capsuled from the beginning, and the same is 

 true of cultures on solid, saccharine media, if the material used has 

 been previously attenuated by being subjected to temperatures below 

 15 C. As has been said, the organism slowly liquefies sugar-gelatine; 

 on peptone-gelatine the same effect is produced, but more rapidly. In 

 neutral media growth is extremely slow, even under the most favour- 

 able conditions otherwise. 



The growing organism is somewhat intolerant of low temperatures, 

 and very susceptible to changes of temperature, a variation of two or 

 three degrees exercising a very marked effect upon the rate of growth. 

 It is probable that the minimum temperature for growth is in the neigh- 

 bourhood of 10 C., and the maximum about 35 C. At a temperature 

 of 22 C., growth is rather slow as compared with some other species, 

 notably B. subtilis, Ehr. The spores are able to withstand a tempera- 

 ture of 100 C. maintained for five minutes. Although the organism 

 is normally aerobic, growth occurs with almost equal vigour in vacua 

 or in pure hydrogen as in air, provided that vigorous material is used, 

 and that both the medium and the temperature are favourable. It is 

 therefore a facultative anaerobe. 



When growing directly on the surface of the gelatine, the colonies 

 tend to take the form of coiled and twisted strands, composed of long, 

 parallel, septate filaments. 



In milk, the organism produces peptonisation and an alkaline 

 reaction, but without coagulation. On potato the growth is spreading,, 

 whitish and slimy or viscous, and consists of non-capsuled rods. Later 

 it becomes dry and cheesy, and eventually distinctly yellow in colour. 



On agar, whether in the presence of sugar or peptone, flat, circular, 

 cheesy colonies are produced, which are tawny in colour, and emit a 

 strong odour resembling melted glue. 



Spores are produced abundantly on various media, the time required 

 varying from twenty-two to seventy hours, according to the medium 

 and the temperature. Spore-formation proper is preceded by peri- 

 pheral condensation of the cytoplasm on the walls of the rod, leaving 

 one or two large central vacuoles. The bulk of the cytoplasm then 

 collects at one end of the rod, minute portions being left behind as a, 

 thin, irregular lining on the walls, and on the septum dividing the rod 

 from its neighbour. The distal portion of the cytoplasm then con- 

 denses, and finally forms an oval spore, occupying an oblique position 

 in one end of the rod, and measuring 2 2'8/x x O m 8 I//. It escapes 

 by the dissolution of the thinner portion of the wall. The spore 



2 D 2 



