210 BACTERIA IN THE MANUFACTURE OF SUGAR 



formed spores 1.8-2.0 /* in diameter, the walls of which coincided with those of 

 the mother-cell. No. 9 of Fig. 54 shows two such cell-chains, each of which 

 exhibits two enlarged members wherein spore-formation has just commenced. 

 When transferred to a favourable medium, these spores were said to burst their 

 solid membrane and then reproduce themselves by fission. Liesenberg and 

 Zopf were, however, unable to discover such spores, and in any case their 



presence would be unimportant, since 

 the organism already possesses in its 

 mucinous envelope an excellent means 

 of protection against adverse influ- 

 ences. Owing to this envelope it is 

 able so Liesenberg and Zopf found 

 to withstand three and a half years' 

 desiccation in the air, and to resist the 

 influence of dry heat at 100 C. for 

 over five minutes ; whereas the naked 

 modification, growing on sliced pota- 

 toes, succumbs after five minutes' ex- 

 posure to a temperature of 75 C. 

 Like other fungi, however, it is much 

 less able to resist moist heat (stearu, 

 heating in liquids), the envelope being 

 readily penetrable by moist warmth. 

 On warming a culture of the gela- 

 tinous form in a nutrient solution up 

 to 88 C. in forty-three minutes, and 

 keeping it at that temperature for 

 five minutes, all the cells were killed, 

 whereas a temperature of 86-87O., 

 under otherwise identical conditions, 

 produced no injurious effect. The 

 naked variety showed itself even 

 somewhat more susceptible; never- 

 theless Leitconostoc mesenlerioides 

 must be classified among the heat- 

 resisting bacteria, by virtue of which 

 property it is enabled to appear in 

 the hot diffusion battery and juice 

 conduits of the sugar-factory. The 

 same faculty of resisting heat may 



also be utilised in preparing a pure culture of the microbe : the sample (a 

 gelatinous lump in a solution of sugar) destined for this purpose being kept for 

 a quarter of an hour at 75 C., by which treatment most of the extraneous 

 germs (adherent to the mucus) are killed, leaving the Leuconostoc unhurt. 



160. Physiology of Leuconostoc. 



The mucinous envelope is soluble in zinc iodochloride, concentrated sulphuric 

 acid, strong caustic potash or soda, or in baryta water, but potassium iodide or 

 iodosulphuric acid produce no noticeable alteration. This fact by itself proves 

 that we have not in this case (as was supposed by Van Tieghem) to deal with 

 cellulose. A beautiful double staining can be produced by first treating the 

 cover-glass preparation with dahlia-violet, which stains the cocci alone, and then 

 immersing it in an aqueous solution of rosolic acid, which is absorbed by the 



FIG. 55. Lenconostoc mesenterioides. 

 , b. chains and bands of the non-capsuled variety, 

 potato culture ; c, e, cells with gelatinous capsule 

 in various stages of development. In d one pair 

 of cells is viewed in the direction of the line join- 

 ing their centres, and hence appears as a simple 

 cell, not as a diplococcus. The shading in c-e 

 merely indicates the configuration of the agglome- 

 rations, and not a stratification of the capsule. 

 Magn. about 1200. (After Liesenberg and Zopf.) 



