84 MICRO-ORGANISMS AND FERMENTATION. 



sometimes become detached (Fig. 24, ^4). Long before a trace 

 of these transverse walls can be observed, staining will show 

 that the organism consists of a series of segments, each of which 

 corresponds to a subsequent individual. The newly formed 

 segment cells are all in the same plane. A division in either 

 one, two or three planes has been observed in certain cocci. 



In the case of many bacteria, formation of spores takes 

 place in the following manner (Figs. 16, I, m; 24, B). The 

 plasma in the cell becomes darker, and often distinctly granu- 

 lar ; a small body subsequently appears frequently at one end 

 of the cell strongly refractive to light, which quickly increases 

 in girth, and is surrounded by a membrane. Meanwhile, by 

 far the greater portion of the remaining plasma of the cell 

 disappears, being used up in the formation of the spore. This 

 is seen enclosed in a clear liquid which gradually disappears f 

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

 withered appendage to the ripe, egg-shaped spore. In many 

 cases a swelling takes place in the mother-cell during spore- 

 formation (Figs. 16, /; 24, B). Before spore-formation begins, 

 the cells of many, especially anaerobic species, are coloured 

 blue with iodine like starch-granulose. Probably at this stage 

 the cells store up reserve food material. Usually only a single 

 spore is formed in a cell. 



One cause for spore - formation is that during vege- 

 tative growth the products of its own activity acids r 

 alkalies, etc. accumulate in the nutritive substratum, and. 

 as a consequence, further vegetative growth is checked. The 

 exhaustion of the nutritive medium may produce the same 

 effect. Spore-formation demands a suitable temperature, 

 and a certain quantity of moisture. The membrane of the 

 spore is very strongly developed, and is frequently surrounded 

 by a gelatinous envelope. The contents are strongly refractive,, 

 and contain but little moisture. Spores are of value in en- 

 abling the species to survive when conditions occur that are 

 unfavourable to vegetative life. They possess quite an 

 extraordinary power of resistance to harmful influences. The 

 membrane cannot be easily moistened or penetrated by water, 

 and the great durability of spores is especially due to the 

 fact that their plasma contains little or no moisture. Thus, 



