CHEMICAL CHARACTERS OF CELL 45 



the characteristics of living things, is not, except in 

 the form of the so-called Brownian movement, 1 

 exhibited by not-living matter. A stone on the 

 moor will not shift its position, nor will any internal 

 movements take place within it, unless the wind 

 or the rain or the action of some other force cause 

 it passively to be moved. Atoms of non-living ma- 

 terial thrown into water will sink or swim accord- 

 ing to their specific gravity, and if they are capable 

 of floating they will be borne down stream or 

 hither or thither as the currents in the water 

 may determine. But the living animal, even of 

 the lowliest character, swims, if he chooses, and it 

 generally does choose, against the stream, whether 

 it does this like the amoeba by the putting forth of 

 temporary processes, or like the ciliata by the 

 waving of tiny permanent projections, or like the 

 fish by the aid of its fins. 



This tendency to move against the stream is 

 called rheotaxy. But thus to name the capability 

 or further to tell us that one of the characteristics 

 of living matter is to react in this way to running 

 water is not to explain the occurrence. Many 



1 These movements, first described by Eobert Brown, the / 

 botanist, are of a vibrating character, but there is no movement , 

 here of transportation as there is in living things, and the move- j 

 ments vary according to the condition of surface tension of the \ 

 fluid in which the fragments say of gamboge are suspended ; \ 

 this tension may be modified by solution of soap for example. 



