THE MECHANISM OF LIFE 493 



the other exciting. The usual result is a decrease of irritability. 

 For example, if a narcotic be allowed to act upon a cell, or if a cell 

 be depressed by over-stimulation, every exciting stimulus will 

 produce a smaller reaction than if it had acted alone ; under 

 certain circumstances the cell will be completely inexcitable. 



But much more interesting are the phenomena that result when 

 two stimuli have the same kind of effect, for example, an excita- 

 tion, but act upon different, and especially upon antagonistic, 

 components of biotonus, that is, one pre-eminently upon dissimila- 

 tion, the other upon assimilation. In such a case the one stimulus 

 inhibits, opposes, restrains the other.^ A striking example of this 

 is afforded by the polar action of the galvanic current upon con- 

 tractile substances, for example, Amceba. The current acts 

 antagonistically at the two j)oles, exciting the amceba-cell to con- 

 traction at the anode, and to expansion at the kathode. This fact 

 can be confirmed with surprising clearness in fairly large fresh- 

 water Ammbce. If a constant current be passed through an amoeba 

 that has been made to contract into a ball by means of strong 

 stimuli, at the moment of making the current the contraction be- 

 gins to give way at the kathode, and phenomena of expansion be- 

 gin to appear, i.e., a large pseudopodium projects ; while at the 

 opposite pole the phenomena of contraction become still more dis- 

 tinct. A sudden reversal of the current suffices to put an immediate 

 end to the processes at the two ends of the body of the Ammba, and 

 to supplant expansion by contraction and contraction by expansion. 

 Analogous phenomena, except with the poles reversed, are exhibited 

 by muscle. We can observe subjectively in the eye the interesting 

 results of excitation of antagonistic metabolic processes. According 

 to Hering's theory of colour vision, the perception of colours is the 

 psychical expression of metabolic jDrocesses taking place in the 

 visual substance, each pair of complementary colours corresponding 

 to antagonistic phases of metabolism. Hence, if two complemen- 

 tary colours be mixed upon the rotating disc of the colour-top, the 

 effect of each ceases, and the whirling disc appears a colourless 

 grey. These facts show that two mutually interfering excitations 

 of antagonistic links in the metabolic chain are able to inhibit or 

 arrest their external effects. In other words, there are two wholly 

 different ways in which the suppression, the inhibition, of a vital 

 phenomenon can be accomplished : on the one hand, by the 

 depression of those components of biotonus upon which it 

 depends ; on the other hand, by the excitation of antagonistic 

 components. 



Finally, it is conceivable that two stimuli will interfere when 

 they act upon antagonistic components of biotonus in opposite 

 senses — i.e., one to excite, the other to depress. The outward 

 result of this would be an augmentation of those vital phenomena 



^ Cy. Verworn ('96, 2). 



