SPONTANEITY. 23 



molecular change along a wire, and produces results at a 

 distance; and many inanimate machines afford examples of 

 the co-ordination of movements for the attainment of 

 definite ends. 



Spontaneity. There is, however, one character belonging 

 to many of the movements exhibited by amoeboid cells, in 

 which they appear at first sight to differ fundamentally 

 from the movements of inanimate objects. This character 

 is their apparent spontaneity or automaticUy. The cells 

 frequently change their form independently of any re- 

 cognizable external cause, while a dead mass at rest and 

 unacted on from outside remains at rest. This difference 

 is, however, only apparent and depends not upon any faculty 

 of spontaneous action peculiar to the living cell, but upon 

 its nutritive powers. It can be proved that any system of 

 material particles in equilibrium and at rest will forever 

 remain so if not acted upon by an external force. Such a 

 system can carry on, under certain conditions, a series of 

 changes when once a start has been given; but it cannot 

 initiate them itself. Each living cell in the long-run is but 

 a complex aggregate of molecules, composed in their turn 

 of chemical elements, and if we suppose this whole set of 

 atoms at rest in equilibrium at any moment, no change can 

 be started in the cell from inside; in other words, it will 

 possess no real spontaneity. When, however, we consider 

 the irritability of amoeboid cells, or, expressed in mechanical 

 terms, the unstable equilibrium of their particles, it be- 

 comes obvious that a very slight external cause, such as 

 may entirely elude our observation, may serve to set going 

 in them a very marked series of changes, just as pulling 

 the trigger will fire off a gun. Once the equilibrium of 

 the cell has been disturbed, movements either of some of 

 its constituent molecules or of its whole mass will continue 

 until all the molecules have again settled down into a stable 

 state. Bat in living cells the reattainment of this state is 

 commonly indefinitely postponed by the reception of new 

 particles, food in one form or another, from the exterior. 

 The nearest approach to it is probably exhibited by the rest- 

 ing state into which some of the lower animals, as the wheel 



