240 Education through Nature 



the blood supply and in the amount and character of 

 other elements of the blood supplying the brain 

 quickly influence not only the character but the rapid- 

 ity of thought. Acuteness of sensation, involving not 

 only perfect sense-organs, but a healthy central nervous 

 system, is, therefore, an essential condition to mental 

 development, inasmuch as it furnishes the material 

 of thought. 



To avoid metaphysical difficulties, many psycholo- 

 gists assume a parallelism between mental and physical 

 states, without affirming any causal connection between 

 them. It is found, for instance, that the mind may 

 influence the body, as in voluntary acts of all kinds. 

 A reciprocal action thus exists which may, perhaps, 

 mean the interaction of the nervous system and 

 organs, as the muscles. This is no less true of other 

 organs of the body, for the stomach may influence 

 the body, and may, in turn, be influenced by it. Such 

 interaction between parts of an organized body is a 

 biological fact which nobody disputes. 



This view of psychology must lead to a recognition 

 of the physical and vital factors in mental processes. 

 Evidently introspection, or the exclusive study of 

 consciousness, as it appears in the adult, can afford 

 no absolute criterion of truth in all intellectual matters. 

 It must be supplemented by objective reality, for that 

 is the condition and occasion of mental processes. 



On the other hand, it is not assumed that the external 

 factor alone can account for the content of conscious- 

 ness. There is in the central nervous system a capacity 

 to react to external impressions ; and this capacity must 

 be sought in protoplasmic organization of a primitive 

 type, in which reside the forces of heredity. 



Mind, having its beginning in comparatively simple 

 reactions to stimuli of all kinds, is found to grow and 

 develop as the body and especially the nervous system 

 grows and develops; and, just as the body requires 



