168 On Light in some of its Relations to Disease. 



out of time, and cannot be made to run true ; but, regulate 

 the tension of this extremely delicate spring, and the 

 movements of the watch become perfect and reliable. 



So the heart may supply the force necessary for the per- 

 fect working of the human machine; but if the tension 

 upon these delicate nerves is not well regulated, there may 

 be such nervous disturbances as seriously to impair the 

 comfort and usefulness of the individual. 



There may be a broken cog or an imperfect wheel in the 

 time-keeper, which, in spite of main-spring or regulator, 

 will sooner or later stop the watch ; and, in the human 

 machine, there may be gross organic lesions which will 

 disturb or destroy its working ; but, excepting these, and 

 other things being equal, the boy or the girl with the best 

 heart and the best eye is most completely armed for the 

 battle of life. 



