56 MICRO-ORGANISMS AND FERMENTATION. 



the cell- wall shrivels up, and only remains as a withered 

 appendage to the ripe spore. In many cases the mother- 

 cell swells up during the spore-formation. This organ is often 

 termed a resting spore (" Dauerspor ") for two reasons : first, 

 because it actually possesses far greater durability and resist- 

 ance to external influences than the vegetative rods [thus, in 

 order to kill the spores of the hay-bacillus (B. subtilis) they 

 must be boiled for three hours at 100C., whilst the vegetative 

 threads are killed at that temperature in twenty minutes] ; and, 

 secondly, because the spore formation generally takes place 

 when the nutriment of the organism appears to be either ex^ 

 hausted 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 tempera- 

 ture 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. 13, 21). 

 The full-grown rod then multiplies in the usual manner. 



Bacteria are now frequently divided into endosporic and 

 arthrosporic 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 genera- 

 tions of vegetative cells separate from the rest and assume the 

 character of spores, immediately, without previous endogenous 

 rejuvenescence, and originate new vegetative generations. A 

 microscopically discernible difference between the arthrospores 

 and the other members, however, occurs only in some cases, in 

 that the walls of the latter spores grow thick (Cladothrix, 

 Leptothrix, Bacterium Zopfii). Perhaps by continued investiga- 

 tion endogenous spores may also be found in all species of the 

 arthrosporic group. It is only a supposition that the bacteria 

 classified above must be considered as analogous to spores. 



Finally, in the morphology of bacteria, we must mention 

 the so-called zooglcea formation (Fig. 13 d). It is known 

 that in all branches of the fermentation industries, in places 

 where cleaning is not strictly attended to, slimy, fatty masses 



