MECHANISM OF NATURE 



potassium, is far richer in potassium than is the 

 soil under the fir tree which has furnished so little. 

 Have maple and fir received their potassium from 

 the air ? Evidently not. 



Again, the brain receives impressions through 

 the nerves, and these impressions are built up into 

 something tangible which may afterward, at any 

 time, reproduce the impression. But the brain that 

 receives impressions and the brain that remembers 

 impressions is the same material brain, and the 

 changes in it are material changes. 



The brain gets tired, and needs time to rest ; then 

 it must be built up of particles which need time 

 to organize and disorganize. 



But it is evident that atoms of elements do not 

 pass through our eyes into the brain to make physi- 

 cal alterations there. 



Yet undoubtedly the sunlight does make material 

 alterations in our brain ; then it must be void mat- 

 ter which passes through eye and nerve into the 

 brain. 



Again, the brain transmits force to the hands; 

 that force which makes the muscles of the hand 

 perform the will of the brain. But every trans- 

 mission of force from one body to another is 

 through a flow of material. (Prop. XVII, B. 1.) 

 Yet organized matter cannot flow through the 

 nerves; then it must be void matter which is dis- 

 organized in the brain and organized again in the 

 hand to pull that valve which sets the muscles to 

 work. 



60 



