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tion of functions. It remains that the seats of functions should be 

 discriminated: the relations of the properties of different seats with 

 each other will principally comprehend their physiology. I shall 

 take only one or two examples with a view to indicate the objects 

 of inquiry. 



14. The method by which we come at the knowledge of the 

 seats of functions of nerves is of the analytical kind. We take an 

 effect, in which we suspect from analogy the offices of nerves to be 

 engaged, and we trace in this system the laws and processes which 

 are exhibited in the instance under consideration. Thus, for example, 

 let the effect be the movement of the muscles of respiration: does 

 the power which animates the muscles of respiration belong to their 

 structure? is it a property of their assimilating life, or is it dependent 

 upon another seat? We find that it ceases upon the division of the 

 phrenic nerves ; and as it is assumed, on grounds before exposed, 

 that division of a structure is a test of the dependence, or the con- 

 trary, on properties which are propagated only by its continuity, so 

 in this case we infer that the action of the muscles of respiration 

 is a function dependent upon the centre of the phrenic nerves. 



15. The inference thus attained is that some properties, ne- 

 cessary to the action of the diaphragm, are derived from the spinal 

 marrow; the next step in our analysis requires that we should 

 specify what these properties are. Before this question can be 

 answered we must have reduced the whole of the properties con- 

 cerned in the effect to certain classes, that we might say, these are 

 the properties inherent in the structure; these are the properties 

 related with them, which, when united, identify the power of respira- 

 tion ; this is a stimulus merely, or a property which is also common 

 to externals, or to many substances; this property is given off from 

 the assimilating life of such a seat ; this is formed by relation of 

 the assimilating life of such a seat with that of a secondary 

 source ; the relation of these properties is direct ; of those, mediate ; 

 these act by affecting the caliber of vessels, or by an operation upon 

 the blood ; those, by modifying its formation. Such definitions as 

 these we must hope to find accurately applied to their examples in 

 the progress of research: the time however, if ever, is distant. We 

 cannot here pursue to any extent the true analytical method, ac- 

 cording to principles of causation, so as to specify of the properties 

 identifying an effect; this change takes place by the addition, this 

 by the abstraction of such properties, leaving the effect to be identi- 

 fied by remaining causes. 



16. There appears, it might be said, to be an inconsistency, or 

 at least some confusion, in the evidence which has in these views been 

 assigned to the experiments of dividing the nervous structures. The 

 inconsistency alluded to is this, if a function in the seat of the in- 

 ferior distribution of a nerve ceases upon a division of the trunk, we 

 infer the dependence of the function upon the centre of the nerve 

 which supplies its seat. If the functions and life of the superior 

 parts of the medulla spinalis cease, after a division of the spinal 



