ix.] BACILLUS. 103 



nothing whatever to do with the exhaustion of the nourishing 

 material, as Buchner seems to think ; for if the conditions ot 

 spore-formation are given, amongst these particularly the 

 exposure to the air, bacilli will commence to form spores 

 long before the nourishing material is exhausted. I will 

 here mention a particular instance to show this. 



Take a test-tube with Agar-Agar peptone, such as has been 

 mentioned in a former chapter as fit for inoculation ; inoculate 

 the surface of the Agar-Agar with hay-bacillus or anthrax- 

 bacillus, place it in the incubator, and keep it there at a 

 temperature of 30 to 35 C. After 36 to 48 hours you will 

 find the surface covered with a good crop of bacilli and lepto- 

 thrix, and in some of them spore -formation is already going 

 on with great vigour. For several days after, the amount of 

 leptothrix increases, and in the filaments large numbers of 

 spores are formed. This goes on for several weeks, long 

 before the nourishing material becomes exhausted. But 

 during all this time the spore-formation is limited only to the 

 surface ; the filaments growing into the deeper strata remain 

 without spore-formation. The same observation can be made 

 with gelatine mixtures of peptone, broth, &c., in the test-tube 

 or in the glass cell described and figured in Chapter V. In 

 the case of the gelatine mixture it is particularly instructive 

 to watch this process, since it clearly proves that the free access 

 of air is essential for the formation of spores. For if the 

 anthrax-bacillus be grown on the (solid) mixture of gelatine 

 and broth described in a former chapter and kept at the 

 ordinary temperature of the room or in the incubator at not 

 more than 22 to 25 C., the spore-formation on the surface 

 occurs only as long as the material remains solid. Anthrax- 

 bacillus as it grows liquefies the gelatine mixture ; in conse- 

 quence of this after some days the superficial layers of the 

 material become fluid, and the bacillar growth, sinking to 



