PHYSIOLOGY OF LEUCONOSTOC 211 



mucinous envelope, the latter then surrounding the blued cells with a rose-red 

 halo. Preparations of this kind sometimes exhibit a scaly stratification of the 

 envelope, the explanation of which is clear : the outer layer of the cell membrane 

 swells up, detaches itself, and now encloses the cell on all sides, so that when 

 this process has been repeated several times the envelope continually increases 

 in size, whilst the dimensions of the bacterial cell itself remain unaltered. By 

 softly pressing the cover-glass of such a zoogloea preparation the cells can be 

 forced out of their mucinous envelopes. 



As already remarked, the substance of which this envelope consists was 

 stated by Scheibler to be dextran, an opinion also shared (as the result of analy- 

 tical experiments) by P. DAEUMICHEX (I.). If, however, we consider the means 

 by which these chemists arrived at their discoveries, doubts will arise as to the 

 accuracy of their conclusions. In all attempts, made by macrochemical means, 

 to determine the composition of the vegetable cell membrane, the same difficulty 

 is encountered, viz., the solution and removal of the cell contents. In order to 

 attain their object, the reagents employed for this purpose must penetrate 

 through the cell wall, and since they come into contact with it whilst still in all 

 their pristine strength, they decompose it more or less effectually. When the 

 lixiviation of the cell contents is completed, then the product remaining behind 

 for ultimate analysis cannot be considered, in point of composition, as unaltered 

 cell-membrane substance, though its form may be still unchanged. This applies 

 to the case now under consideration. In order to obtain the substance of the 

 mucinous membrane in a pure condition Scheibler boiled the gelatinous mass 

 (freed from adherent sugar) with milk of lime, and found that only a small por- 

 tion was dissolved. This fact of itself bears evidence against the (chemical) 

 uniformity of the substance of the mucinous envelope of Leuconostoc. It is also 

 probable that even the dextran recovered from the lime extract is a decomposi- 

 tion product of a more readily hydrolised constituent of the said membrane. 



The behaviour of this fission fungus towards sugars merits special considera- 

 tion. It has already been stated that the formation of mucus occurs only in 

 such nutrient media as contain grape- or cane-sugar, the other carbohydrates, 

 tested on this point by Liesenberg and Zopf, being found unsuitable. Leuco- 

 nostoc mesenterioides produces invertin, which then splits up the cane-sugar; so it 

 may be surmised that the development of the gelatinous membrane can only occur 

 in presence of grape-sugar (and perhaps also fructose !). This does not, however, 

 imply that lactose, maltose, and dextrin are unaffected by this fission fungus ; 

 on the contrary, it ferments them and forms lactic acid, a faint evolution of 

 gas being at the same time noticeable. The presence of a small quantity (3-5 

 per cent.) of calcium chloride in the nutrient medium favours the production of 

 mucus and the fermentative activity of the organism, the latter being brisker 

 when oxygen is excluded. The optimum temperature for the development of 

 this microbe being between 30 and 37 C., it is evident that in order to kill 

 this pest the juice in sugar- factories must be kept at higher temperatures. 

 Leuconostoc consumes a certain portion of the cane-sugar, and as it also produces 

 invertin, which forms invert sugar the presence of which is well known to 

 seriously retard the crystallisation of the cane-sugar another source of loss to 

 the sugar-manufacturer arises. Molasses naturally forms a highly suitable 

 nutrient medium for this microbe. The speed at which it increases therein is 

 reported (from practical experience) as follows by E. DURIN (I.) : A wooden vat, 

 previously used as a recipient for beet-juice, and the walls of which were covered 

 with a thin film of mucus (i.e. zoogloaa of Leuconostoc) was charged with 50 h.l. 

 (i 100 galls.) of neutral molasses. At the end of twelve hours the whole of this had 

 become converted into a mucinous coherent mass. This microbe also gives rise 

 to mischief in the refineries as well as in the raw-sugar works. F. STJIOHMEK (I.) 



