456 THIRD PART. BACTERIA OR SCH1ZOMYCETES. 



throughout or with the exception of certain transverse zones which do not turn blue ; and 

 in both cases the substance which has become blue spreads uniformly through the 

 protoplasm, without forming bodies in it of definite shape. This phenomenon has 

 been observed when the nutrient substratum contains starch, and when it is entirely 

 free from starch. The amyloid substance . disappears with the formation of spores. 

 This amyloid reaction with iodine occurs in Hansen's vinegar-forming Arthrobacterium 

 (Bacterium) Pastorianum, and occasionally in Leptothrix buccalis *, but without proof 

 of any connexion with spore-formation ; it is not found in the majority of the forms 

 which have been examined, nor is there any report of the occurrence of amyloid bodies 

 in the species which contain chlorophyll. 



Nuclei have not as yet been observed in Bacteria. 



The protoplasm of the Bacteria is surrounded in all cases, so far as we can de- 

 termine, by a membrane. In the case of cells or cell-rows which vegetate actively 

 in a fluid as isolated bodies and do not become cemented together into large 

 masses the cell-wall appears on the lateral faces of the protoplasmic body as a thin 

 bounding surface'; on the boundary lines of cylindrical cells closely united in rows it 

 is a septum,- which is in many cases only to be distinguished by the use of desiccating 

 and colouring reagents, and is so entirely invisible in the living specimen that a 

 cell-row composed of several cells looks like a homogeneous unsegmented cylinder. 



This delicate membrane immediately clothing the protoplasmic body must, in 

 some forms at least, and especially in some species of Spirillum, be highly extensible 

 and at the same time elastic. The straight cylindrical body in these species is often 

 seen to bend strongly backwards, and then to recover its former direction. According 

 to the views which prevail at the present day it is the protoplasm only that can be 

 supposed to be the active cause in this phenomenon, and the investing membrane 

 must possess the qualities just mentioned to be able to follow its movements. 



Few or more probably no vegetating cells of Bacteria are clothed with this delicate 

 membrane alone at the highest stage of their development. This is only the inner- 

 most lamella of a membrane which increases in thickness, and in doing so swells 

 and becomes gelatinous in its outer portions. Such gelatinous outer layers or invest- 

 ments are found wherever care is taken to observe them, and direct examination 

 shows that they are either connected in the manner indicated with the delicate inner 

 membrane or are formed from it. 



The particular character of the gelatinous envelope varies in the different species 

 within wide limits. In the freely moving rod-like cells of the typical Bacteria it is 

 invisible, but it can be recognised in the flakes of slimy matter formed by larger 

 accumulations of these forms. In other cases it is of greater thickness and firmer 

 consistence, and may either form distinct gelatinous sheaths round isolated cells and 

 aggregates of cells, or unite and cement the cells together into larger gelatinous 

 masses. 



The chemical composition of these gelatinous membranes would appear to be 

 very different in different species. Low - found that the membranes of the mother of 



1 See Zopf, Spaltpilze. 



8 Nageli, Ueber d. chem. Zusammensetzung d. Hefe (^Sitzgsber. d. Miinchener Acad., Mai, 1871) ; 

 Id., Theorie d. Gahrang, p. in. 



