PREFACE. 5 



stincts, the passions, and the will, impel various portions of the 

 animal to perform the actions intended by the Creator in uniting 

 the machines with a thinking force ? If the doctrines of the first 

 part of this work (which are, however, an imperfect sketch of 

 the elements of the science of the laws which regulate the in- 

 fluence of the mind on the body) be compared with what our 

 physiologists have hitherto produced, it will be seen that^ as yet, 

 this whole science has been in some degree a waste field. 



As regards the other animal motive forces, with the exception 

 of the conceptions, there scarcely was a notion until the time 

 of Haller, who at least pointed out their existence ; and yet the 

 doctrine of irritability, which that great man has taught, com- 

 prises only a portion of those animal motive forces which are 

 independent of the mind, as the whole of the Second Part of 

 this work will sufficiently prove. The laws of action of these 

 forces have not as yet been illustrated by any one, and the first 

 elements thereof which this Second Part contains, exhibit to us 

 a large and fertile branch of science with which medical art can 

 and must ultimately be enriched, if Physiology — that science 

 which has to elucidate the mechanism of animal bodies com- 

 pounded of such multifarious motive forces — is ever to be freed 

 from at least existing defects. It was always premature to 

 attempt to explain the natural actions of the animal body 

 (which are brought about by the common operation of physical, 

 mechanical, and animal forces), by the laws of physics and 



I machines, so long as there were no principles by which to 

 judge of the co-operation of the proper animal forces; but 

 especially premature to attempt their elucidation by the aid of 

 untenable, imperfect opinions, and inadmissible suppositions, 

 when the principles of physics and mechanics were found to be 

 insufficient. Thus Stahl erred, who knew well the necessity 

 there was for the co-operation of the animal forces with the 

 mechanism of the animal body, because it did not occur to him, 

 that it possessed other animal motive forces besides the influ- 

 ence of the mind on the body. So also the mechanical phy- 

 sicians erred, who would deduce all natural phenomena from 

 the physical and mechanical forces of the elements of the animal 

 organism, and absolutely deny the manifest influence of the 

 mind and of the other purely animal forces on animal acts. 

 So at this moment physiologists err, when they exclude the 



