50 THE DATA OF BIOLOGY. 



plicable without assuming any more special agency. Con- 

 sidering that in creatures of the genus Noctiluca, for example, 

 to which the phosphorescence most commonly seen on our 

 own coasts is due, there is no means of keeping up a con- 

 stant circulation, we may infer that the movements of 

 aerated fluids through their tissues, must be greatly affected 

 by impulses received from without. Hence it may be that 

 the sparkles visible at night when the waves break gently on 

 the beach, or when an oar is dipped into the water, are called 

 forth from these creatures by the concussion, not because of 

 any unknown influence it excites, but because, being propa- 

 gated through their delicate tissues, it produces a sudden 

 movement of the fluids and a sudden increase of chemical 

 action. 



Nevertheless, in other phosphorescent animals inhabiting 

 the sea, as in the Pyrosoma and in certain Annelida, light 

 seems to be produced otherwise than by direct re-action on 

 the action of oxygen. Indeed, it needs but to recall the now 

 familiar fact that certain substances become luminous in the 

 dark after exposure to sunlight, to see that there are other 

 causes of light-emission. 



§ 20. The re-distributions of inanimate matter are habitu- 

 ally accompanied by electrical disturbances; and there is 

 abundant evidence that electricity is generated during those 

 re-distributions of matter that are ever taking place in 

 organisms. Experiments have shown "that the skin and 

 most of the internal membranes are in opposite electrical 

 states ; " ?ind also that between different internal organs, as 

 the liver and the stomach, there are electrical contrasts : such 

 contrasts being greatest where the processes going on in the 

 compared parts are most unlike. It has been proved by 

 du Bois-Eeymond that when any point in the longitudinal 

 section of a muscle is connected by a conductor with any 

 point in its transverse section, an electric current is estab- 

 lished; and further, that like results occur when nerves are 



