30 THE TONER LECTURES. 



by which these results are brought about must remain largely 

 a matter of speculation. The eflect of emotion and intellectual ac- 

 tion upon circulation and temjjerature can be, and have been, 

 directly studied, but the intimate molecular changes which accom- 

 pany such functioning cannot he directly determined. We know 

 that an over-worked muscle will sometimes atrophy, and not only 

 so, but also that the supplying nerves and their central nuclei will, 

 in extreme cases, undergo degeneration. Every mental act is asso- 

 ciated with some molecular change in the gray matter of the cere- 

 bral convolutions. When mentalization proceeds beyond the limits 

 which are practically fixed for every individual, exhaustion, defect- 

 ive nutrition, and sometimes cell-atrophy result. Too prolonged 

 drains upon energy will exhaust and saj) the nutrition of nerve- 

 cells anywhere. In cases of mental over-work tissues fail to regene- 

 rate as fast as they break down. "A thought," says Dr. H. C. "Wood,^ 

 " is the index-hand that marks the death of a proto^Dlasmic mole- 

 cule, or rather of protoplasmic molecules, for the production of a 

 thought is usually a complex process involving many molecules. 

 Normally, this molecule, or these molecules, are removed and re- 

 placed by the processes of nutrition as fast as they are destroyed. 

 If, however, thought folloW'S thought with such instant rapidity 

 that no time is allowed for the reproduction of protoplasmic mole- 

 cules, by and by so many molecules or working units will have 

 been used up as to produce a constantly growing scarcity of those 

 normal particles which are capable of building up the new working 

 units that shall replace those which have been lost by continuous 

 mental efforts." 



Many of the symptoms of nervous break-down, and many of the 

 diseases induced by mental overstrain, are symptoms and diseases 

 referable to the organic nervous system. These are doubtless pre- 

 cipitated by exhaustion or direct lesion of the centres of the or- 

 ganic functions situated in the medulla oblongata. It is to the im- 



1 Brain Work and Over-work. 



