154 MICRO-CRGANISMS AND DISEASE. [CHAP. 



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 repre- 

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

 they have an ample supply of oxygen. If this latter con- 

 dition 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 tempera- 

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

 limit. Pasteur states that in a nutrient medium exposed to 

 a temperature 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 44 5 C., as I have con- 

 clusively 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- 

 formation has set in. Under the most favourable conditions, 

 each cubical or rod-shaped mass of protoplasm includes one 

 spore, in which case the bacillar filament contains an almost 

 unbroken row of spores ; but in other cases only an elemen- 

 tary mass here and there contains a spore, the rest breaking 

 down and becoming absorbed. In the first case also, the 

 protoplasm of the elements almost entirely disappears, the 

 sheath swelling up and becoming hyaline, and only the 

 bright spores remaining. Their linear arrangement, however, 

 still indicates that they were formerly contained in one 

 filament. 



