172 TEXT-BOOK OF BACTERIOLOGY. 



rate of increase can continue unabated till checked by exhaustion 

 of the nutritient medium. 



It has a considerable motile power, which is shown in a 

 very peculiar way. The rods do not glide elegantly and smoothly 

 through the fluid, but throw themselves, as it were, from side to 

 side, and " waddle '" across the field of the microscope. The Bacillus 

 subtilis is one of the species in which the organs of motion have 

 been distinctly seen as flagella at either end of the rods. 



Under some circumstances, as yet but imperfectly understood, 

 the Bacillus subtilis proceeds to sporulation. The appearance of 

 the spore-bearing cell usually undergoes no change, yet the fully- 

 formed' spores, though considerably shorter than the mother cell, 

 are often somewhat broader and thicker. They are formed in the 

 middle of the rods. They are egg-shaped bodies, which have a 

 very brightly-gleaming appearance and a high degree of resisting 

 power. On silk threads they retain their vitality unimpaired for 

 years. They outlive an exposure for above an hour to dry heat of 

 120 C., and are equally insensible to the influence of chemical sub- 

 stances. The process of sporulation is very peculiar in the Bacillus 

 subtilis. The strong envelope of the spore bursts transversely at 

 the middle, but instead of being 1 completely severed, it remains un- 

 divided at one point. The young cell then escapes, as Prazmowski 

 has observed, from the gaping aperture at right angles to the 

 longitudinal axis of the spore. According to De Bary, the budding- 

 cell, when it has attained a certain length, makes an evolution of 

 90, and protrudes at right angles to the rupture in the membrane. 

 The expanding new cell, by the hindrance which the tough spore 

 membrane opposes to its extension, is forced to turn toward the 

 ruptured opening in the middle and to seek exit there. 



The hay bacillus belongs to the strictly aerobic species : it can 

 thrive between great extremes of temperature, from 10 to 45 C.; 

 its optimum is about 30, which is also the best temperature for 

 sporulation, while the g-ermination of the spores takes place be- 

 tween 30 and 40 C. The rods take the anilin stain, and its spores 

 are particularly well adapted for double staining. 



If we grow Bacillus subtilis on the glass plate, small white dots 

 at first appear, which, under the microscope, appear as irregularh r - 

 rounded, green-shining, slightly-granulated masses. Yet the 

 growth of this micro-organism is so energetic that this first 

 stage is of short duration. Very soon the colonies expand rapidly 

 and reach the surface of the gelatin, which they quickly and ex- 

 tensively liquefy, thus offering the true characteristic forms of hay- 

 bacillus colonies. With the naked eye one sees the small pure cul- 



