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ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. (559 



branches are subdivided into the lenticular, lenticulo-striate, and 

 lenticulo-lhalamic arteries. These vessels pass to their terminations 

 without anastomosing with one another. One of the lenticulo-striate 

 arteries which passes through the outer part of the putamen is very 

 frequently the seat of hemorrhage. By Charcot it has been named 

 the artery of cerebral hemorrhage. 



The lymph finds its way out of the various areas of the brain by 

 means of perivascular spaces in the tunica adventitia of the blood- 

 vessels. These spaces communicate with the subarachnoid space at/ 

 the surface of the brain. 



PHYSIOLOGY OF THE NERVOUS SYSTEM. 



Comparison of Nerve and Muscle. In the study of the general 

 physiology of muscle there was first analyzed its most apparent phe- 

 nomenon: muscular contraction. Then the forces which provoke 

 muscular contraction were considered, with modifications of muscular 

 excitability. 



Practically the same course will be adopted in treating of the 

 neral physiology of tke nerves. First there will be considered that 

 property comparable to the muscular contraction ; in turn will follow 

 a study of the forces which produce the nerve-wave, with modifi- 

 tions also of the nervous excitability. 



Thus, there will be established a sort of parallel between nerv- 

 ous and muscular functions; muscular contraction and nerve-wave; 

 muscular irritability and nervous irritability; muscular excitability 

 and nervous excitability. 



When a nerve is separated from its nervous centers and no force 

 tervenes to modify its state, then it will remain inert. There will 

 neither movement nor sensibility. Neither will the nerve come 

 to action unless it be stimulated or excited. 



Nerve Excitability. When a stimulus is applied to a nerve it 

 ters into activity. There are various ways in which this activity 

 manifested, as by modification of motion or sensation, and besides 

 ese external manifestations a latent property in the nerve itself, 

 own as negative variation, which it undergoes during activity, 

 e most striking exhibit of nerve activity is the contraction of the 

 uscle supplied by the nerve. If we would estimate the irritability 

 a nerve it is necessary to know accurately both the intensity of 

 stimulus and the result produced. Irritability requires for its 

 e manifestation the integrity of the nerve and an unimpaired circu- 

 tion and nutrition. But even in a normal state the irritability of the 



