THE INTIMATE STRUCTURE OF THE CELL ijg 



It is probable that cilia are not formed, and that motility is 

 due to the power of contractibility which is inherent in 

 protoplasm, and which here finds expression. 



Thioporphyra volutans (Ellis). 



Each organism is composed of either a single cell, or less 

 frequently, of a diplococcus, or very rarely a tricoccus. The 

 single cell is either spherical or ovate, and its diameter is 

 approximately 7/x. 



The membrane is well defined, and appears to be the outer 

 limiting layer of the cytoplasm ; it takes the colour more deeply, 

 apparently because its consistency is denser than that of the 

 cytoplasm. Its outer layers turn readily to a slimy material 

 which forms a loose irregular mantle enveloping the coccus. 

 The mantle is best observed when the cell is treated with the 

 Giemsa stain. It is too thin and too delicate in texture to be 

 regarded as a regular sheath, and it may be remarked that 

 most, if not all, bacterial cells of the Euhacteria possess a 

 similar covering. As is the case with Beggiatoa alba, solid 

 objects such as sulphur globules readily pass out of the cells. 



The cytoplasm is reticulate and readily stained. The dis- 

 position of the protoplasmic matter is described on page 153. 

 It is finely granular, and diftused through its substance is 

 a purple colouring matter which varies in tint from a deep 

 violet to a mauve colour. It is visible in individual cells only 

 if the pigment is intense. There is no nucleus. 



Motility is effected by means of a single long and strongly 

 developed cilium (Fig. 34/). Probably, as in Chromatiiim, this 

 cilium is composed of several cilia united by a common 

 envelope of slime. 



The sulphur globules which are formed in the cytoplasm 

 may be scattered throughout the cell, or grouped at one spot. 

 If the cell is ovoid, the grouping is at one of the poles (Fig. 

 34c). In appearance, size, and reactions they resemble the 

 sulphur globules of Beggiatoa alba (see Fig. 34 a — d, Fig. 35 a — e). 

 It is only the outer portion of the globule that is composed of 

 sulphur. Each contains a central core of organic matter which 



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