EFFECTS OF EXERCISE. 1 5 5 



The germinal matter taking part in mental action, like 

 other forms, is no doubt liable to defective as well as irregular 

 and monstrous growth, even during and after the adult period 

 of life. These changes, which may be temporary or per- 

 manent, are probably more under the immediate influence 

 of the will than is the case as regards changes in other 

 forms of germinal matter. But there can, I imagine be 

 little doubt that, just as by exercise up to, and in many 

 cases even after, the middle period of life, we are enabled 

 to increase the power of certain muscles and the perfec- 

 tion of certain movements which are associated with in- 

 creased formation of nerves and nerve-cells in the nerve 

 centre governing them : so, by habitually indulging in 

 certain trains of thought, we may perhaps effect the 

 increase of the germinal matter concerned, until at last 

 this preponderates so much over other portions taking part 

 in other kinds of mental action that it alone is exercised, 

 while the rest remains hardly active at all or quite dor- 

 mant. Every lunatic asylum affords what I conceive to be 

 examples of this, and it is not impossible in certain 

 instances to distinguish the cases in which the mental 

 living matter itself is deranged from those in which the 

 mechanism concerned in the expression of ideas is the 

 seat of disease. On the other hand, what remarkable 

 instances do we meet with of the gradual but continuous 

 improvement of the mental powers even in advanced life, 

 where they have been subjected to unremitting but judi- 

 cious exercise from early youth onwards ! 



The mental excitement and incoherence, followed by 

 complete suspension of mental powers, which occur in 

 inflammation and other conditions where the germinal 



