I30 PROTOPLASMIC ACTION AND NERVOUS ACTION 



combination; a good illustration is the water-soluble red 

 pigment of Arbacia eggs, echinochrome, which is con- 

 tained chiefly in minute round chromatophores scattered 

 throughout the protoplasm. That this material is free 

 to diffuse is shown, however, by the fact that cytolytic 

 action, even temporary, causes its rapid diffusion into 

 the surroundings; and. complete loss of pigment may 

 thus result. The localization or condensation of the 

 pigment in the chromatophores indicates apparently 

 that it is present there in some form of loose chemical 

 combination or adsorption; but in any such case an 

 equilibrium between the adsorbed and the dissolved 

 compound must exist (Cads = KCs{f). Presumably the 

 dissolved portion of the pigment is homogeneously 

 distributed throughout the protoplasm, hence the 

 chromatophores adsorb (or combine) equal quantities 

 and are similar in appearance. But any local decrease 

 in the concentration of dissolved pigment, due to diffusion 

 through the altered plasma membrane, disturbs the 

 adsorption equilibrium and leads to the liberation of the 

 adsorbed pigment, which may thus be completely lost 

 from the cell. The conditions are similar in any other 

 case of reversible adsorption. 



Hermann's observations on the difference between the 

 transverse and the longitudinal conductivity of nerve 

 fibers also indicate the higher conductivity of non- 

 partitioned protoplasm as compared with partitioned. 

 He found that the current encounters several times the 

 resistance when the fibers are placed transversely between 

 the electrodes, as compared with fibers arranged length- 

 wise, with equal distances between the electrodes and 

 equal sectional areas of tissue. The same is true for 



