GROWTH AND DECAY OF MIND. 329 



training. The growth and development of mental power in the indi- 

 vidual, and the process by which, after attaining a maximum of power, 

 the mind gradually becomes less active, until in the course of time it 

 undergoes at least a partial decay, form the special subjects of which 

 I propose now to treat ; but, in order to form clear ideas on these sub- 

 jects, it will be necessary to consider several associated matters. In 

 particular, it will be desirable to trace the analogy which exists be- 

 tween bodily and mental power, not only as respects development 

 and decay, but with regard to the physical processes involved in their 

 exercise. 



It is now a well-established physiological fact that mental action 

 is a distinctly physical process, depending primarily on a chemical re- 

 action between the blood and the brain, precisely as muscular action 

 depends primarily on a chemical reaction between the blood and the 

 muscular tissues. Without the free circulation of blood in the brain, 

 there can be neither thought nor sensation, neither emotions nor ideas. 

 It necessarily follows that thought, the only form of brain-action which 

 we have here to consider, is a process not merely depending upon, but 

 in its turn affecting, the physical condition of the brain, precisely as 

 muscular exertion of any given kind depends on the quality of the 

 muscles employed and affects the condition of those muscles, not at 

 the moment only, but thereafter, conducing to their growth and de- 

 velopment if wisely adjusted to their power, or causing waste and de- 

 cay if excessive and too long continued. It is important to notice 

 that this is not a mere analogy. The relation between thought and 

 the condition of the brain is a reality. So far as this statement affects 

 our ideas about actually existent mental power, it is of little impor- 

 tance ; for it is not more useful to announce that a man with a good 

 brain will possess good mental powers than to say that a muscular 

 man will be capable of considerable exertion. But as it is of extreme 

 importance to know of the relation which exists between muscular 

 exercise and the growth or development of bodily strength, so it is 

 highly important for us to remember that the development of mental 

 power depends largely on the exercise of the mind. There is a " train- 

 ing " for the brain as well as for the body — a real physical training — 

 depending, like bodily training, on rules as to nourishment, method 

 of action, quantity of exercise, etc. 



When we thus view the matter, we at once recognize the signifi- 

 cance of relations formerly regarded as mere analogies between men- 

 tal and bodily power. Instead of saying that, as the body fails of its 

 fair growth and development if overtaxed in early youth, so the mind 

 suffers by the attempt to force it into precocious activity, we should 

 now say that the mind suffers in this case in the same actual manner — 

 that is, by the physical deterioration of the material in and through 

 which it acts. Again, the old adage, " mens sana in corpore sano," 

 only needs to be changed into " cerebrum sanum in corpore sano," to 



