8o4 THE POPULAR SCIENCE MONTHLY. 



forehead of Jove. They are the children of a slower evolu- 

 tion. Each organ performs its function so perfectly because 

 of the discipline of use, because of the slow discipline of long- 

 continued use. We recognize this in the matter of the actions 

 called physical. We build gymnasiums on this principle, and 

 lay out our athletic grounds accordingly. The runner wants 

 well- developed nerve and muscle, and he wants the habit of 

 rapid action. The champion in every sport needs the human 

 apparatus, the nerve and sinew, and he also needs the habit of 

 prompt exercise. It is the same with the bodily organs and func- 

 tions. Strong lungs come from deep breathing and the pumping 

 of maximum quantities of air. If we want a strong stomach we 

 must give it work to do. We must eat cheese and nuts and other 

 foods that are hard to digest. It will never do to live on pep- 

 tones. All this is very obvious. But it is less obvious when we 

 come to speak of the operations of the spirit. Yet the case is 

 quite the same. We need the organ and, through exercise, the 

 well-developed function. Our thinking is connected with molecu- 

 lar changes in the brain and spinal column. It will depend upon 

 these and upon the degree of their organization. But thinking is 

 a complex operation. It may be resolved into simpler elements, 

 into sensations. But even here it no longer suffices to say that 

 these sensations are transmitted to the brain. This language is 

 entirely too general. Their destination may be specifically 

 stated. They go to a particular part of the brain, depending on 

 their nature. 



With respect to the outer world, we have but one sense, and 

 that is the sense of touch. All our impressions are tactile. The 

 outer world has for us but one mode of operation, and that is 

 through motion. The organs of sense are attuned to different de- 

 grees of motion, and unerringly pick out their own notes. The ear, 

 sensitive enough to the coarse air waves which constitute sound, 

 is utterly deaf to the minute light waves which so easily affect the 

 eye. The ego touches the outer world only at its own bodily ex- 

 tremities. What it comes in contact with is motion. For us, 

 then, the outer world is coextensive with motion, and with only 

 so much motion as we can perceive. The outer world has differ- 

 ent dimensions according to the sensitiveness of this power of 

 perception. The motion to which we do not respond is an unseen 

 and unknown world an undiscovered country. The motion to 

 which we do respond makes up our entire world. It is our uni- 

 verse. 



The impressions gathered by the several senses are transmitted 

 to the brain over their appropriate nerve routes. Here at this 

 central station the same exquisite division of labor prevails as at 

 the outlying stations on the circumference. In receiving sensa- 



