112 MICRO-ORGANISMS AND DISEASE. [CHAP. 



never form spores, but when grown on the surface with free 

 access of air, or on solid media (e.g. serum gelatine, gelatine 

 broth, Agar-Agar, potato, &c.), the bacilli, having devsloped 

 into filaments, proceed to form spores. But they may form 

 spores even in fluid media if by some accident, either by 



FIG. 79 FROM AN ARTIFICIAL CULTURE OF BACILLUS ANTHRACIS IN BROTH 

 AFTER MANY DAYS INCUBATION. 



The threads are swollen and curled up, and in many places the protoplasm has 



disappeared, leaving the sheath and septa distinct. 

 Magnifying power 700. (Stained with Spiller s purple.) 



sticking to the glass vessel containing the fluid or by means 

 of a cotton-wool fibre, some of the bacilli remain on the 

 surface of the fluid. This formation of spores is not due to 

 exhaustion of the nourishing medium, as is maintained by 

 Buchner it has, in fact, nothing to do with it but represents 

 the last stage in the life-history of the bacilli, provided they 

 have an ample supply of oxygen. If this latter condition is 

 not fulfilled, as when they are grown at the bottom of a fluid, 

 the bacilli gradually degenerate as mentioned above. 



Spore-formation occurs, cceteris paribus, at all temperatures 

 between 18 and 45 C. Koch found 15 C. the lower limit. 

 Pasteur states that in a nutrient medium exposed to a tem- 

 perature of 42 to 43 C. the bacilli are not capable of forming 

 spores ; but this is not correct, for when the bacilli are 

 growing on the surface of the nutrient medium, they form 

 spores even at a temperature of 44 to 45 C., as I have con- 

 el n lively shown by growing them on Agar-Agar and peptone 

 mixture. The spore-formation consists in the appearance of 

 a bright glistening spherical body in the protoplasm of' an 

 elementary mass or cell ; this body gradually enlarges till it 

 reaches its full size, becoming at the same time oval. The 

 bacilli at these points are thicker than where no spore- 



