394 BACILLI WHICH DO NOT CAUSE FEBMENTATION. 



other species isolated by Miller have not as yet heen 

 published in detail. 



With regard to the pathogenic bacteria present in the 

 buccal secretions, see pages 319, 322 and 325 ; as 

 regards Spirochaete denticola, see below. 



Bacilli which are not known to produce Specific 

 Fermentations. 



Bacillus subtilis. 

 (Hay bacillus.) 



Hay bacillus. These are cylindrical rods, up to 6 /x. in length, and on 

 an .average about three times as long as they are thick. 



Morphological They grow and divide very rapidly; the length of time 



characters. between one fission and a second is, at 21 C., about an 

 hour and a quarter, and at 35 C. about 20 minutes. 

 Pseudo-threads frequently appear, which can be fre- 

 quently seen to be made up of rods, by the fact that 

 they soon become bent in a zig-zag manner; in other 

 cases, however, they do not present this appearance. 

 The individual members of a thread are as a rule in 

 different stages of growth and subdivision, and are 

 therefore of different lengths. Under various conditions, 

 which have not as yet heen accurately ascertained, the 

 rods begin to swarm; the movements are active and 

 snake-like. At each end of the rod a fairly long and 

 twisted flagellum can be seen, especially after treatment 

 with haematoxylin (Koch). When the substratum 

 becomes poorer in nutrient material the continued 

 multiplication of the rods by fission gradually ceases, 



Spore forma- and then as a rule spore formation commences. At one 

 part of the rod which has now ceased to move a dark, 

 shaded part becomes evident, sometimes more in the 

 middle, sometimes more towards one end, and ultimately 

 this portion becomes converted into a highly refracting 

 spore with dark outlines. The rods swell up at the 

 same time in some cases in an almost unnoticeable 

 manner. At the same time that the spores are formed 

 the contour of the rods becomes dull and indistinct, and 



