SECT. II 



PHYSIOLOGY 



293 



trary, the whole protoplasmic body is not involved, but it possesses 

 special organs of motion in the form of whip-like flagella or CILIA. 

 These may be one, two, four, or more in number, and arranged in 

 various ways (Figs. 97, 98). They extend through the cell wall when 

 this is present and move very rapidly in the water, imparting con- 

 siderable velocity to the protoplast, often giving it at the same time 

 a rotary movement. The minute swarm-spores of Fuligo varians tra- 

 verse 1 mm. (sixty times their own length) in a second, those of Ulva, 

 0"15 mm., while others move more slowly. The Vibrio of Cholera, 

 one of the most rapidly moving bacteria, takes 22 seconds to traverse 

 a millimetre. 



Although plants which are firmly attached and stationary exhibit 

 no such locomotory movements, the protoplasm within their cells 

 does possess a power of movement. Such internal protoplasmic 

 movements are especially active in the non-cellular Siphoneae, and in 

 non-septate Fungi, in the elongated internodal cells of the Characeae, 

 in the hairs of many plants, as well as in the leaf-cells of some aquatic 

 plants (cf. p. 58). 



In tliese movements the outermost layer of protoplasm in contact witli the cell- 

 wall remains at rest; the movement cannot thus be compared to that of an 

 amoeba enclosed in a cell. The movement continues 

 when the protoplasm has been detached from the 

 cell-wall. Its cause must be looked for in surface 

 tensions between the protoplasm and the cell-sap. 



The continuance and activity of such protoplasmic 

 movements, the existence of which was first observed 

 by CoiiTi in 1772, and later rediscovered by Tke- 

 viRANUS in 1807, ai-e dependent on factors which, 

 in general, support and promote the vital activity ; 

 the presence of free oxygen in aerobionts and proper 

 conditions of temperature seem to be particularly 

 favourable to them. That the movements in Nitella 

 continued for weeks in the absence of oxygen is 

 explained by the power the Characeae possess of be- 

 coming facultative anaerobes. Those Bacteria which 

 are obligate anaerobes lose their power of motion in 

 the presence of oxygen. On the other hand aerobic 

 Bacteria which lose their motility in the absence of 

 oxygen become motile again on the supply of oxygen 

 being restored (cf. p. 214). From the study of sections 

 in the cells of which currents had been induced in 

 the })roto[<lasm, by the injuries sustained in their 

 preparation and by other abnormal conditions, grave 

 errors have arisen concerning the existence of such 

 protoplasmic movements in cells, in which under normal conditions they cannot 

 be observed. The presence of protoplasmic currents in a cell may, in fact, indicate 

 either an energetic vital activity, or, on the other hand, be merely a symptom of 

 a pathological or, at least, of an excited condition of the [irotoplasm. 



Fio. Tl'2. — Streaiiiiny protoplasm 

 in the hypliae of lihhupus i: igii- 

 cans. (After J. C. Arthur.) 



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