THE FISSION FrNGl 493 



organic inaterial is ternicil a saprophyte,^ and wlicn the 

 chemical changes induced by its activity are offensive the 

 process is putrcfaction.- 



The motile rods multiply rajjidly so long as there is any 

 food available or until the putrid products become so concen- 

 trated as to be harmful to the plant. Then the plants rise 

 to the surface of the liciuid, lose their swimming organs, 

 form long threads by remaining attached end to end after 

 fission, and at the same time they secrete a gelatinous covering 

 which binds them all together into a rather firm la3-er or 

 scum (.4). While in this stage resistent resting spores are 

 formed in many of the cells, by the protoplast becoming round 

 and secreting a new cell-wall iC). If the liquid is allowed to 



* ' .-•. •/•-' •'-. 



Fig. 32.3. — Milk-souring bacterium {BacterLum ticidi laciici. Rod-germ 

 Family, Bactcriacco:). Plants stained, ^^A (Migula.) — Causes the 

 souring of railk by converting the milk-sugar into lactic acid. 



evaporate and the scum to dry it will become more or less 

 powdery, and slight currents of air may then carrjr away 

 minute bits containing many of these excessively small spores 

 which no mere drying can harm. Myriads of such spores are 

 floating about in the air around us. When a Bacillus spore 

 falls into any putrescible liciuid it germinates bj- elongation 

 of the protoplast and the development of swimming lashes, 

 thus forming a motile rod like that already described. 



Very similar to Bacilli, both in structure and life-history, 

 are the many forms of the genus Bacterium which differs 

 from Bacillus mainly in lacking swimming organs. Bac- 

 terium acidi lactici (Fig. 323) causes milk to sour bj' convert- 



' Sap'ro-phyte < Gr. sapros, rotten. 



- Pu"tre-fac'tion < L. pulris, rotten; facere, make. 



