TRANSLATOR'S INTRODUCTION. iii 



in preparation, and may therefore be considered as the work of 

 a powerful metaphysical intellect, in the prime of its strength, 

 and thoroughly informed on the subject to which it had been 

 so long, so perseveringly, and so assiduously directed. With 

 the exception of a reply to various reviews of the work,^ Unzer 

 wrote no more on his favorite subject, but turned his atten- 

 tion to the pathology of contagion, and contagious diseases, 

 which he elucidated with his usual acuteness. He died, rich, 

 April 22, 1799, being a week less than 72 years old. 



Having thus given a brief sketch of Unzer's literary career, 

 I will notice, as shortly as possible, the origin and progress of 

 his peculiar views, as finally perfected in this, his greatest work. 

 Although he must have been eminently qualified by natural 

 endowments, and by a natural bias to metaphysical research 

 for grappling successfully with the profound and very difficult 

 questions of physiological metaphysics, it is probable, that to his 

 early associations at the University of Halle we owe the special 

 direction of his mind to the subject. Both Hoffmann and Stahl 

 were professors at Halle for a lengthened period; but when 

 Unzer commenced his medical studies, the former was still 

 professor, at the venerable age of 79, and died at Halle, in 

 his 83d year, so that Unzer must have known him personally. 

 It was, however, as the pupil of Juncker, an avowed Stahlian, 

 that he specially directed his attention to the metaphysics of 

 vital actions, and to him Unzer dedicated his defence of the 

 doctrines of Stahl, in a long and highly complimentary 

 dedication. At this time physiology, and especially the phy- 

 siology of the nervous system, was fast losing its purely 

 hypothetical character, and assuming the rank of a science. 

 Mental philosophy had long taken cognisance of the different 

 kinds of motion in animals of which every man is led to dis- 

 criminate at least three : — namely ; 1st, those dependent solely 

 on the will ; 2d, those of which he is conscious, but which are 

 independent of the will as the exciting cause; 3d, those of 

 which he is wholly unconscious, and which can neither be excited 

 nor restrained by volition. The first class of actions could be 

 readily ascribed to the soul ; but the second and third classes, 



' Physiologische Untersuchungen auf Veranlassung der Gottingisclien, Frank- 

 furter, &c. Recensionen seiner Physiologic der thierischen Natur. — Leipzig, 1773. 



