AUTONOMOUS LOCOMOTORY MOVEMENTS 539 



This cohesion, which is at least noticeable in the surface layer, renders it 

 questionable whether we ought to regard it as liquid at all, and whether we may 

 therefore refer alterations in its form to surface tension only. The assumption 

 of an alternation in the condition of the protoplasm from a semi-solid to a liquid 

 state expresses most accurately our present knowledge of the subject. If 

 amoeboid movement is chiefly occasioned, as we are bound to believe, by surface 

 tensions, it must be pointed out at the same time that these tensions are doubt- 

 less initiated not by the environment but by the protoplasm itself. When the 

 medium in which a plasmodium lies is made perfectly homogeneous, movements 

 still go on in the plasma, and, conversely, a quiescent plasmodium remains un- 

 changed even when alterations in the medium are effected which are calcu- 

 lated to modify its surface tension very greatly (Pfeffer, 1890, p. 275). 



As in the case of growth phenomena, so also in locomotory mov^ements, 

 the environment plays a great part [compare Ewart, 1903]. Many of these 

 external factors are the essential formal conditions, without which locomotion 

 cannot take place. These, or other factors, influence the direction of the move- 

 ment, so that we may divide locomotory phenomena into autonomous and induced. 



The presence of a certain amount of water is one of the most important of 

 the formal conditions of locomotion, for it must be at once apparent that water 

 often acts as the medium in which the movement is carried out. Furthermore, 

 the protoplasm must also itself contain a certain amount of water of imbibition 

 in order that streaming or ciliary motion may take place. Rotation and circula- 

 tion, it is true, do not cease at once when the cell is plasmolysed, but the resting 

 condition of the peripheral layers may be observed with special clearness in such 

 plasmolysed cells. Ciliary movement also still continues m plasmolysed Bacteria, 

 but if a 5 per cent, to 10 per cent, solution of potassium nitrate be employed to 

 bring about plasmolysis a rigor sets in, which has been termed by A. Fischer 

 (1894, p. 75) ' drought-rigor ', and which disappears when the water is again 

 replaced. Similar rigor phenomena have been observed by Fischer in fiagella, 

 when these are treated with certain substances, e.g. acids, or when there is 

 a deficiency in nutrients ; narcotics such as ether, as might be expected, produce 

 similar results. Similarly, observations on amoeboid movement show that it, 

 too, ceases when the protoplasm is affected by narcotics, weak ammonia, &c. 



Among all the substances which influence movements the action of oxygen 

 is perhaps the most interesting. In many cases the presence of oxygen is an 

 absolutely essential condition for the performance of such movements, but that 

 applies only to aerobic organisms. The anaerobes referred to above cease to 

 move in presence of traces of oxygen, while facultative anaerobes exhibit move- 

 ments of very varying intensity when oxygen is withdrawn. There is thus no 

 essential interdependence between movement and growth, for some facultative 

 anaerobic Bacteria, according to Ritter (1898), grow very well without oxygen, 

 forming fiagella which, however, move only when oxygen is present. Other 

 facultative anaerobes move, for a time at least, without oxygen and, if well 

 nourished, their capacity for movement is maintained for a much longer period 

 than if starved. Doubtless the energy required for this movement arises from 

 intra-molecular respiration, for the continuance of which the presence of sugar is 

 necessary. According to Celakowski (1898), Pelomyxa continues to move for 

 72 hours in absence of oxygen, Oscillaria for 24 hours, Chara for 18 hours, and 

 Elodea for 1-4 hours, while the protoplasmic movements in the staminal hairs 

 of Tradescantia come to a standstill at once when oxygen is withdrawn. 

 KuHNE'sresearches (1898) on Characeae prove that even closely related organisms 

 behave very differently in this respect, for some species continue to exhibit move- 

 ments, employing intra-molecular respiration, only for hours, others for weeks. 

 A few organisms, e.g. the chromogenic Bacteria investigated by Ewart (1897), 

 have the special power of fixing oxygen loosely and making use of this reserve 



