30 THE POPULAR SCIENCE MONTHLY. 



But the more frankly the student of natural science acknowledges 

 these appointed limits, and the more humbly he is reconciled to this 

 ignorance, the more profoundly conscious is he of his right inductively 

 to fashion his own views as to the relations between mind and matter, 

 with perfect freedom, and untrammeled by myths, dogmas, or time- 

 honored philosophies. 



He sees material conditions in a thousand ways influencing mental 

 life. To his unprejudiced mind there seems no reason to doubt that 

 sense-impressions are really communicated to the so-called Soul. He 

 sees the human mind grow with the brain as it were, and, according 

 to the empiricists, he finds that the actual forms of his thought are 

 constituted.by means of external perceptions. In sleep, and in dreams, 

 in fainting, in intoxication and narcosis, in the delirium of fever and 

 in inanition, in mania, epilepsy, idiocy, microcephaly — in a thousand 

 morbid states he sees the soul to be dependent on the constant or tran- 

 sient condition of the brain. ISTo theological prejudice prevents him, 

 as it did Descartes, from recognizing in the souls of animals the rela- 

 tives of the human soul, and less perfect members of the same series 

 of development. On the contrary, he sees that in the vertebrates 

 those parts of the brain which physiological research and pathological 

 experience prove to be the seat of the higher mental activities keep 

 pace, in their comparative development, with the growth of these 

 activities. "Where mental capacity makes the immense leap from the 

 anthropoid apes to man which is indicated by the power of speech, we 

 find a corresponding leap in cerebral mass. The varied arrangement 

 of similar elementary particles in the invertebrates instructs the inves- 

 tigator of Nature that here, as in other organs, there is question less 

 of the general architecture than of the structural elements. 



With awe and wonder he regards the microscopic molecule of 

 nervous substance which is the seat of the laborious, constructive, 

 orderly, loyal, dauntless soul of the ant. Finally, the development 

 theory, coupled with the doctrine of natural selection, forces upon him 

 the theory that the soul came into being as the result, gradually at- 

 tained, of certain material combinations, and that probably, like other 

 heritable endowments that are of use to the individual in the struggle 

 for life, it has risen and perfected itself up to its present state through 

 a countless series of generations. 



Now, if the ancient thinkers found every interaction between body 

 and soul unintelligible and impossible on their theories, and if their 

 undoubted simultaneous cooperation is to be explained only by a Pre- 

 established Harmony of the two substances, then the notion they 

 formed of the soul, in conformity with their scholastic conceptions, 

 must have been erroneous. The necessity of a scholastic conclusion 

 so plainly in conflict with the reality, is, as it were, an apogogical 

 demonstration of the falsity of their premises. In his simile of the 

 two watches, Leibnitz, as has been well observed by Fechner, over- 



