MORPHOLOGY OF THE ACETIC ACID BACTERIA 297 



and soon develops fine implications. That of B, Kiitzingianum resembles the 

 first species, but differs therefrom in raising itself high above the surface of the 

 liquid by gradually climbing up the walls of the vessel. Fresh differences make 

 their appearance when a small portion of the skin is examined under the 

 microscope. Whilst the cells of B. Kiitzingianum are, for the most part, single, 

 and are only rarely seen joined together as chains, those of the other two species 

 are seldom found as separate cells. The cells of B. aceti (Fig. 81) are somewhat 

 more slender, and frequently exhibit the sand-glass or figure 8 form (" en huit") 

 noticed by Pasteur. In B. Pasteurianum (Fig. 82) they are mostly rather longer 

 and considerably broader (plumper) than those of the other two species. 



These bacterial pellicles are true zoogloea, i.e. the individual cells are attached 



FIG. 81. Bacterium aceti. 



Cells from a freshly formed skin on 

 " doppel-bier." 



Mag-n. 1000. (After Hanscn.) 



FIG. 82. Bacterium I'asteurianmn. 



Cells from a freshly formed skin grown at 34 C. 

 on '-doppel-bier." 



Magn. 1000. (After Honsen.) 

 FIG. 83. Bacterium Kiitzing-ianum. 



Cells from a freshly formed skin grown 

 at 34 C. on " doppel-bier." 



Magn. 1000. (After Hansen~). 



together by a mucinous envelope, formed by the swelling and mutual fusion of 

 the external layers of the cell membranes, in which the cells then become 

 embedded. In ordinary (unstained) preparations the presence of this envelope 

 is only deducible from the mutual cohesion of the cells ; it can, however, be 

 rendered visible by suitable treating and staining, e.g. by Loefflei-'s method. 

 Fig. 8 (p. 31) was drawn from a preparation of this kind. 



The behaviour of the mucinous envelopes of these three species towards iodine 

 solution (iodine in water or alcohol or potassium iodide) is worthy of notice ; those 

 of B, Pasteurianum and B. Kiitzingianum are thereby stained blue, whilst that of 

 B. aceti remains unaltered. The point must be emphasised that it is the mucinous 

 envelopes and not the true cell membranes that are stained in this manner. The 

 cell plasma is in all three cases coloured yellow ; consequently the preparations 

 all exhibit yellow cells after the iodine treatment, these cells being embedded in 

 the case of B. aceti in a colourless matrix. In B. Pasteurianum and B. Kiitzingi- 

 anum this latter is blue, and to the unaided eye the appearance of the whole 



