72 MICRO-OKGANISMS AND DISEASE. [CHAP. 



described in a former chapter and kept at the ordinary tem- 

 perature 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 consequence of this 

 after some days the superficial layers of the material become 

 fluid, and the bacillar growth, sinking to the bottom of the 

 fluid layer, is thus removed from the surface. The spores 

 which were freely formed while the growth went on on the 

 surface, germinate again into bacilli, but because these have 

 now sunk into the depth, although rapidly multiplying and 

 growing into filaments, they cease to form any spores. 1 



Bacilli which are not possessed of the power of locomotion 

 (i.e. are without a flagellum) when sown into the depth of a 

 fluid or solid material, if they have no chance, accidental or 

 otherwise, of reaching the surface, do not as a rule form spores ; 

 but there are some such bacilli which, although not growing 

 on a free surface, nevertheless form spores, e.g. the bacillus 

 butyricus or amylobacter (Prazmowski). Some putrefactive 

 bacilli occurring after death in the abdominal organs (intestine, 

 kidney, spleen, liver), and in fluid exudations within the peri- 

 toneal and pleural cavities, show also spore-formation ; probably 

 they get their oxgyen from the tissues. Anthrax-bacillus, 

 however, never forms spores except it is growing well exposed 

 to the outer air. 



The bacilli which are possessed of a flagellum (e.g. hay- 

 bacillus, bacillus of putrefaction) generally form a pellicle 

 on the surface, and in this pellicle copious spore-formation 

 goes on. 



The spores first formed, when shaken down into the fluid, 

 again germinate into bacilli, and there multiply. The last 

 pellicle formed in a culture, before exhaustion, represents the 

 last crop of spores ; and these, owing to the exhaustion of the 

 nourishing fluid, remain as spores, only capable of germinating 

 into bacilli when new nourishing material is added, or when 

 they are transplanted to new nourishing material. 



It is a rule that wherever the spores are formed they ger- 

 minate into bacilli if they have access to nourishing material ; 

 but if not, or if the nourishing material is exhausted, they 

 remain as spores. Spore-formation does not take place at low 

 temperatures. Koch found in the case of anthrax -bacillus 

 that a temperature below 12 C. prevents the formation of 

 spores. Pasteur states that in the case of anthrax-bacillus 

 spore- formation does not take place above 40 C. ; never for 

 1 Report of the Medical Officer of the Local Government Board, 3881. 



