BACTERIA. 55 



does a species occur in this or that particular form ? Upon 

 this point we know very little at present. 



In the case of many bacteria multiplication by spores 

 takes place in the following manner. The plasma in the 

 cell becomes darker, and often distinctly granular ; after that 

 a small dark body appears, which quickly increases in size, 

 and at the same time becomes strongly refractive ; mean- 

 while by far the greater portion of the plasma of the ceil 

 disappears, becoming used up in the formation of the spore ; 

 this is seen enclosed in a clear liquid, which gradually 

 disappears ; finally, the cell-wall shrivels up, and only remains 

 as a withered appendage to the ripe spore. This organ is 

 often termed a resting-spore (Dauerspore), for two reasons, 

 namely, first, because it actually possesses far greater 

 durability and resistance to external influences than the 

 vegetative rods ; and, secondly, because the spore formation 

 generally takes place when the nutriment of the organism is 

 either exhausted or unfavourable to the further vegetative 

 growth of the latter ; the spores, then, serve to preserve the 

 life of the organism during this critical period. 



As soon as favourable conditions of nutriment and tem- 

 perature again occur, the spores germinate. They first 

 increase in size, and the contents lose their strong refractive 

 power. A bacterium then grows out from the spore, the wall 

 of which is sometimes seen to burst or divide into two shells 

 (Figs. 10, 13). The full-grown rod then multiplies in the 

 usual manner. 



Bacteria are now sometimes divided into endosporous and 

 arthrosporous bacteria, of which the first-named form their 

 spores in the interior of the vegetative rods, whilst in the 

 latter group no such interior spore-formation has hitherto 

 been observed ; in these forms, members of a series of united 

 generations of vegetative cells separate from the rest and 

 assume the character of spores immediately without previous 

 endogenous rejuvenescence, and become the origin of new 

 vegetative generations (for instance, Bact. aceti). Perhaps 



