258 OF THE NERVOUS SYSTEM. 



laws of development from a much more extensive point of view, intro- 

 ducing the doctrine of the paramount influence of physical causes in this 

 respect, and perhaps we shall find ourselves brought to the conclusion 

 that the progressive career of a cell is absolutely dependent on the phys- 

 ical conditions to which it is exposed, and that there is nothing extraor- 

 dinary in the circumstance that two cells placed under conditions which 

 are alike will develop alike ; that, therefore, a part which is being repaired 

 will have its additions made in the same places, of the same material, to 

 the same extent, and of the same form as the part which has been re- 

 moved. 



CHAPTER XIV. 



OF THE NERVOUS SYSTEM. 



Divisions of the Nervous System. Cerebro-spinal and Sympathetic. Fibrous and Vesicular. 



Structure and Functions of Nerve Fibres. Centripetal and Centrifugal. Rate of Conductlbillty. 



Anatomical Examination of the Structure and Functions of Nerve Vesicles. They diffuse Influ- 

 ences, are Magazines of Force. Element of Time Introduced by Registering Ganglia. Oxida- 

 tion necessary to Nerve Activity. Necessity of Repair and Rest. Electrical Examination of 

 the Functions of Vesicles. Anatomical and Electrical Examinations agree. 



Automatic Nerve Arc. Cellated Nerve Arc. Multiple Arcs. Commissures. Registering Nerve 

 Arcs. Sensorlum. Influential Arc. 



Suggestions derived from cerebral Structure respecting the Soul. Its Independent Existence and 

 Immortality. 



Ideas of Time and Space. Objective, subjective, and Impersonal Operations. Vestiges of Im- 

 pressions and their Interpretation. Finite Nature of Knowledge. Mental Emotions. 



THE parts and functions which have been thus far described stand in 

 Im ortanceof subordination to the important system on the study of which 

 the nervous we now enter. It may be truly said that the position of any 

 animal in the scale of life is directly dependent on the de- 

 gree of development of its nervous system. Through this it is brought 

 in relation with the external world, deriving sensations or impressions 

 therefrom ; through this, also, all voluntary muscular contraction takes 

 place. Whatever the grade of intelligence may be, the degree of devel- 

 opment or expansion of the nervous system is in close correspondence 

 thereto, from the lowest conditions in which it is first making its appear- 

 ance in tribes which are scarcely distinguishable from vegetable forms, 

 up to its highest elaboration in the cerebro-spinal system of man. 



The physiologist has to confess that in this, which is, without doubt, 

 imperfect con- ^ e mo ^ t important part of his science, the amount of what is 

 dition of the known with exactness is limited : indeed, so great an obscu- 

 BU Je rity rests upon the functions of the nervous system that he 



has to content himself rather with the description of structure than offer 



