8 PRINCIPLES OF PHYSIOLOGY. 



forces ; but the second^ in reference to the nerve-forces^ inde- 

 pendently of the mind; out of these a third division arises, 

 which describes the animal nature as an independent whole, 

 compounded of these two animal forces. 



The First Part is devoted exclusively to the animal-sentient 

 forces of the animal machines above-mentioned ; and an epitome 

 of the general doctrines applicable to the brain and nerves, 

 and to the animal spirits and their general properties, is 

 concisely given in the First Chapter and the beginning of 

 the Second. The animal- sentient forces are considered with 

 reference to their action, in two ways ; namely, partly per se, 

 as they themselves act in the animal machines, — the brain 

 and nerves, — and partly in reference to their influence on the 

 mechanical machines, with which the nerves are incorporated. 

 These constitute the contents of the Second and Third Chapters ; 

 to these may be added the Fourth, in which the connection of 

 the conceptive force and the animal moving forces, or in other 

 words, of mind and body, is generally set forth. 



The whole philosophy of the reciprocal influence of body 

 and mind, as laid down in our works on Physiology, is as yet 

 imperfect, being without true principles, and partly confusedly, 

 partly erroneously, propounded. Probably this has arisen from 

 the little acquaintance of physicians with theoretical philosophy 

 except physics, and still less with psychology; as if mental 

 philosophy were not necessary to the science of the nature of 

 man^s organism. Nevertheless, our physiologists have only 

 worked at the useless subtilties mentioned before, and the 

 only useful knowledge which they teach as to the union of 

 body and soul, refers to the external sensations, and also to 

 the imaginations and passions. There are others who aspire, 

 with Bonnet, rather to analyse the different mental faculties 

 by means of movements in the brain, of which we are totally 

 ignorant, than to study what is peculiarly within the sphere of 

 the physician, and investigate the laws according to which the 

 faculties act in the body; which, nevertheless, can be easily 

 learnt by observation, if people would only cease from the 

 attempt to deduce them from inscrutable principles. 



These doctrines present a somewhat different appearance in 

 the present work. I have endeavoured to define the laws by 

 which the various faculties of the mind operate either through 



