VAEIOUS GROWTH-FORMS OF BACTERIA 



37 



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consists of a structureless, irregular lump of jelly containing bacteria 

 inside it, and its surface may be either smooth or folded. In nature, 

 a zoogloea may be formed from individuals of one species only 

 (homogeneous zoogloea), or several species may have contributed to 

 its formation (heterogeneous zoogloea). When the mucilaginous 

 material is liquefied, the imprisoned bacteria assume once more their 

 normal activities. This condition must be regarded as one in which 

 the formation of mucilage has been much more active than cell- 

 division. 



The best known example of the zoogloea condition is that of Leuco- 

 nostoc mesenteroides (now called Streptococcus mesentero'ides). This 

 coccus forms huge slimy masses in 

 nutrient solutions which contain sugar, 

 and much damage has been done by it 

 in sugar mills, for in the sugar solution, 

 before it is crystallised and refined, this 

 organism finds a most suitable medium. 

 The cocci are formed in chains (Fig. 55), 

 hence the original name Leuconostoc 

 has now been dropped and that of 

 Streptococcus substituted. 



Another well-known case is that of 

 the Kefir grains. These bodies, when 

 placed in milk, cause fermentation to 

 take place, with the result that a small 

 percentage of alcohol is produced. A 

 Kefir grain is a lump of mucilaginous 

 matter consisting of several kinds of 

 organisms, chiefly bacterial, and is 

 therefore a heterogeneous zoogloea. 



Much attention has been given to 

 the question of the existence of Pho- 

 morphism among bacteria. This term 

 refers to the capacity whereby a 



single species is enabled to assume different forms. Among the fungi, 

 the Uredineae and Ustilagineae show very marked pleomorphism. 

 The various forms of one of these plants are so different that 

 it is difficult to believe that they all belong to the same species. 

 Among bacteria, however, pleomorphism of the same kind as is found 

 in the above-named fungi does not exist. What we do find in some 

 species is a remarkable variety in the forms that may be assumed by 



Fig. 55. — Streptococcus mesente- 

 roides. (a) Appearance when mucilage 

 is not developed ; (6)zoogloea condition. 



