LEUCONOSTOC MESENTERIOIDES. 273 



detected endospores in his Leuconostoc, and asserted that in un- 

 favourable media some of the cells increased in size, and formed 

 spores 1.8-2.0 p 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 influences. 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 modifica- 

 tion, growing on sliced potatoes, 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 (steam, heating in liquids), 

 the envelope being readily penetrable by moist warmth. On 

 warming a culture of the gelatinous 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 86-87 C., under otherwise identical condi- 

 tions, produced no injurious effect. The naked variety showed 

 itself even somewhat more susceptible ; nevertheless, Leuconostoc 

 mesenterioides 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 Leueonostoc. 



The mucinous envelope is soluble in zinc iodochloride, concen- 

 trated sulphuric acid, strong caustic potash or soda, or in baryta 

 water, but potassium iodide or iodosulphuric acid produce no notice- 

 able alteration. This fact by itself proves that we have not in 

 this case (as was supposed by Yan 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 mucinous envelope, the latter then sur- 

 rounding the blued cells with a rose-red halo. Preparations of 

 this kind sometimes exhibit a scaly stratification of the envelope, 



VOL. I. 8 



