460 GENERAL PHYSIOLOGY 



verse galvanotaxis has not been observed thus far, although it is 

 scarcely doubtful that it will yet be found to occur in other 

 unicellular organisms. 



C. THE PHENOMENA OF OVER-STIMULATION 



When the Athenians, under the leadership of Miltiades, had 

 gained the victory of Marathon, one of the soldiers named Eukles, 

 still hot from the struggle, hastened from the battle-field to Athens 

 in order to be the first to bring to his countrymen the news of the 

 victory. Plutarch ^ who has given us the anecdote, tells of 

 the dramatic fate of this runner of Marathon. When Eukles 

 entered Athens exhausted by the effort of the long run, he still 

 had power to call out to his countrymen the news of the victory 

 in the words " Xalpere, xO'lpofiev ! " whereupon he fell dead. One 

 of our modern sculptors, Max Kruse, has illustrated this tale by 

 his figure of the runner of Marathon now in the National Gallery 

 at Berlin, and has given striking expression to the physiological 

 phenomena of total exhaustion. 



The cause of the tragic end of Eukles was his excessive 

 muscular exertion. Under the influence of long duration or 

 great intensity of stimuli, changes gradually appear in the living 

 substance which, when they have reached a certain extent, lead 

 to death. In the following pages we will examine somewhat in 

 detail the phenomena resulting from over-stimulation. 



1. Fatigue and Exhaustion 



If a living object be stimulated by long-continued, oft-repeated, 

 or very strong stimuli, after some time it passes into the condition 

 of fatigue. The general characteristic of fatigue is a gradual 

 decrease of the irritability of the living substance. This is 

 expressed especially in the fact that with increasing fatigue, the 

 intensity of the stimulus remaining the same, the result of the 

 stimulation becomes constantly less. 



We have already become acquainted with some examples of 

 this fact in considering galvanic stimulation.^ If a constant 

 current of average strength be passed through an Actinospkccriuin, 

 at the moment of making there begin to appear at the anode 

 marked phenomena of contraction. The protoplasm of the 

 pseudopodia flows centripetally until the latter are dra\vn in. 

 Then the walls of the vacuoles break ; and a granular disintegra- 

 tion of the protoplasm results, which proceeds constantly farther 

 from the kathode during the passage of the current. This dis- 

 1 Of. bibliography. ^ Of. pp. 422 and 423. 



