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TEXT-BOOK OF PHYSIOLOGY. 



teoses and serum-globulin), and a compound pyrocatechin, capable 

 of reducing copper salts, though not exhibiting any other of the 

 properties of sugar. In many respects this fluid resembles lymph. 

 The subarachnoid space and the general encephalic cavities, termed 

 ventricles, communicate with one another by an opening in the pia 

 mater (the foramen of Magendie) as it passes over the lower part 

 of the fourth ventricle. 



The Functions of the Central Nerve System. The functions 

 of the central nerve system are twofold: (i) It coordinates the 



organs and tissues of the body in such 

 a manner that when a stimulus is 

 applied to one structure it gives rise to 

 activity in another. (2) It serves to 

 bring the individual into conscious 

 relationship with the external world. 



The coordination of the organs and 

 tissues is accomplished mainly by the 

 intermediation of the spinal cord and 

 the medulla oblongata. The reflex 

 activities connected with digestion, 

 the circulation of the blood, with res- 

 piration, excretion, etc., are illustra- 

 tions of the coordinating capabilities 

 of the nerve-centers located in these 

 portions of the central nerve system. 



Consciousness of the existence of 

 the external world and of the relation 

 existing between it and the individual 

 is associated with the physiologic activ- 

 ities of the encephalon, and more 

 particularly of the cerebral hemi- 

 spheres. This portion of the nerve 

 system is the chief, though perhaps not 

 the sole, organ of the mind, and its 

 main functions are for the most part 

 mental. The function of a part at least 

 of the peripheral nerve system is to 

 afford a means of communication 

 between the central nerve system and the remaining structures of 

 the body. The nerve-trunks constituting this part may be divided 

 into two groups, as follows: 



i. The first group comprises nerves in connection with the special 

 sense-organs, e.g., eye, ear, nose, tongue, skin, as well as nerves 

 in connection with the general or organic sense-organs, e. g., mu- 

 cous membranes, viscera, etc., which transmit nerve impulses 



FIG. 202. THE MEMBRANES OF 

 THE SPINAL CORD. i. Dura 

 mater. 2. Arachnoid. 3. 

 Posterior root of spinal nerve. 

 4. Anterior root of spinal 

 nerve. 5. Ligamentum den- 

 tatum. 6. Linea splendens. 

 (Morris, after Ellis.} 



