266 A. E. HILTON ON THE CAUSE OF REVERSING CURRENTS 



advancing extremities of the network are bordered with wavy or 

 fanlike expansions, at the margin of which the plasm coming 

 through the hyaline threads of the network collects in irregular 

 ridges with constantly changing outline. We also observe in the 

 creeping plasmodium that while plasm masses diminish in the 

 parts towards the rear, new aggregations arise in more forward 

 positions ; the network acting both as channels for the fluid and 

 flowing interior plasm, and a means of locomotion of the entire 

 plasmodium, the veins being withdrawn from behind, while ex- 

 tending in the lines of advance. The significance of this 

 unequal distribution into irregular and fluctuating masses, 

 communicating by attenuated connections, will presently appear. 



If the plasmodium has been cultivated for convenience on a 

 flat piece of glass, and is viewed under the microscope by 

 transmitted light, with a magnification of sixty to a hundred 

 diameters, the sight presented is a striking one. The network 

 veins, and other expansions of plasm sufficiently thinly spread to 

 be semi-transparent, exhibit, in their interior, a rhythmic series 

 of alternate flowing movements, made visible by more opaque 

 granules carried along by the currents. The streaming com- 

 mences slowly, accelerates until it rushes impetuously, slackens 

 speed until it comes to a standstill, pauses as if hesitating, and 

 then reverses its course. Each alternation occupies, on an 

 average, about a minute and a half ; but, as we should expect, 

 the flow in the direction in which the plasmodium is creeping is 

 rather longer and stronger than in the opposite direction. 



This spectacle of streaming life-currents is singularly im- 

 pressive. The oscillating rhythm of pause and rush is curiously 

 fascinating, and in the mind of a thoughtful observer the 

 question almost inevitably arises, "Why do not the opposing 

 forces which alternately propel these currents counteract each 

 other, instead of operating in turn, causing these remarkable 

 reversals ? " 



When the problem is stated in that simple way, we see at 

 once that the solution we seek must of necessity be a physical 

 one, leading up to a physiological one ; because although the 

 phenomenon is, in the first place, obviously physical, it is certain, 

 action and reaction being equal and opposite, that physics cannot 

 furnish the full explanation. What, then, are the physical 

 facts, and the physiological solution they suggest ? 



