XXXVI INTRODUCTION. 



qual in force, do not blend into one, the double impres- 

 sion upon them. In proof of this, it is common to see 

 mental derangements depending on the compression of 

 -a hemisphere by effused blood, by pus, by depressed 

 bone, and by an exostosis from the internal face of the 

 cranium. Even where every sign of compression is 

 removed, the hemisphere occasionally takes a long time 

 to regain its action, so as to recover from the alienation. 



This harmony of action exists also in the organs of 

 locomotion, and of voice; and any thing which inter- 

 rupts their symmetry destroys the precision with which 

 their functions are executed. 



Opposed to this harmony in the shape and functions 

 of the organs of animal life, the most striking differ- 

 ences may take place between the organs of organic 

 life, without much disturbance in the general result. 

 For example, in disparities of the kidneys, of the lungs, 

 of the salivary glands, &c., their functions are not, by 

 any means, the less perfectly performed. The circu- 

 lation remains the same in the midst of the frequent 

 varieties of the vascular system on the two sides of the 

 body, whether those varieties exist naturally, or whe- 

 ther they depend upon artificial obliterations of the 

 large vessels, as in aneurism. 



Another very striking difference in the two lives may 

 be observed in the duration of their action. All the ex- 

 cretions proceed uninterruptedly, though not uniformly. 

 Exhalation and absorption succeed each other incessant- 

 ly; assimilation and dissimilation follow the same rule. 

 On the other hand, every organ of animal life, in the ex- 

 ercise of its functions, has alterations of activity and of 

 complete repose. The senses, fatigued by long appli- 

 cation, are, for the time, disqualified from farther action. 

 The Ear is no longer sensible of sounds : The Eye 

 is closed to Light ; Sapid bodies no longer excite the 



