16 IRRITABILITY 



by a comparatively simple mechanism. The analysis of this 

 shows a difference in the intensity of the exciting or depressing 

 effect produced by the stimulus. The stimulus exerts its influence 

 unequally upon the specific activity of the motor elements of 

 different parts of the surface of the cell body. This difference 

 in response causes the axis of the freely moving organism to 

 assume a different direction in which to move. It is compelled 

 to move in a definite direction and so, in this field, the apparently 

 mysterious attraction and repulsion of living organisms toward 

 stimuli has, by means of the most simple analysis, been robbed 

 of its mystical character. 



Finally, I should like to touch briefly upon a view of the irri- 

 tability of living substance which has recently been brought for- 

 ward by Semon} It assumes the proportions of a whole system 

 and is proclaimed as a basis for the comprehension of organic 

 phenomena. It originated with an idea which Hering^ developed 

 many years ago and which later was accepted by Haeckel,^ 

 namely that heredity is a species of memory of the living sub- 

 stance. Semon attributes to living substance, in contrast to non- 

 living, a "Mneme." By "Mneme" he understands the capability 

 of living substance to assume, through the influence of a stimulus, 

 a permanently altered condition. The latent alteration resulting 

 from the stimulus he terms "Engramm." These "Engramms" 

 can later, however, not only be activated by the reapplication of 

 the original stimulus, but also by other stimuli, so that the state 

 of excitation once brought about by the original stimulus reap- 

 pears. Semon calls the reproduction of the state of primary 

 excitation by a later stimulus "Ekphorie." A great number of 

 other new word formations, such as "chronogene Engramme" 

 " phasogene Ekphorie,'' "mnemische Homophonie/' "mnemisches 

 Protomer" and countless ^others are supposed to serve for the 

 better understanding of a series of special facts, chiefly in the 



1 Semon: "Die Mneme als erhaltendes Princip im Wechsel des organischen Gesche- 

 hens." Zweite verbesserte Auflage, Leipzig. 



2 Ewald Hering : "Uber das Gedachtniss als allgemeine Function der organischen 

 Materie." Wein 1876. 



3 Ernst Haeckel: "Die Perigenesis der Plastidule oder die Wellenzeugung der 

 Lebenstheilchen." Berlin 1876. 



