BIONOMICS 245 



And thus we obtain further explanation of the extreme 

 cases of sexual dimorphism and of that remarkable abnormal 

 increase of size in certain types during palaeontological periods, 

 which we have already set down to the cumulative effects of 

 anti-symbiotic forces liberated by food substances obtained 

 otherwise than by a due (biological) reciprocal differentiation. 

 The study of surface-energy shows that the discharge of ions 

 of various direction by the minute colloid particles of our food 

 is indeed a most important and (in the long run) determinant 

 factor. Plant and animal being biological (and chemical) 

 opposites, it easily follows that there is normally a corre- 

 sponding difference of charges anabolic and katabolic in 

 their constituent particles. A normal colloidal charge would 

 direct an organism symbiogenetically ; the cumulative effect of 

 undesirable components in colloidal charges is to determine the 

 organism pathogenetically, with varying effects upon form. 

 Frequently, when opposing pulls of this kind are present, 

 the equilibrium struck by the species frequently is one 

 represented by sexual dimorphism antithesis of form 

 in male and female and likewise by an antithesis of 

 form as against the normal biological kin of the species, i.e., 

 those that have remained symbiotic and cross-feeding, and 

 therefore do not present dimorphic or monstrous ("terato- 

 logical ") developments. 



To return now to Spencer. Considerations of " nerve- 

 force " and its genesis involve him in considerable difficulties 

 which his physico-chemical method is apparently unable to 

 solve. 



Heat, light and electricity are emitted by inorganic matter when 

 undergoing changes, as well as by organic matter. But there is a kind 

 of force manifested in some classes of living bodies, which we cannot 

 identify with any of the forces manifested by bodies that are not alive 

 a force which is thus unknown in the sense that it cannot be assimi- 

 lated with any otherwise recognised class. I allude to what is called 

 nerve-force. 



This is habitually generated in all animals, save the lowest, by 

 incident forces of every kind. The gentle and violent mechanical 

 contacts, which in ourselves produce sensations of touch and pressure 



