30 TIII; \KKvors SYSTKM AND ITS CONSERVATION 



has its nucleus in the gray mutter, do we do well to call 

 the portion about the nucleus the cell and to imply that 

 the core of the fiber is not to be reckoned ;i - belonging to 

 it'.' It is reasonable to claim that the cell should be held 

 to include all its extensions, no matter how prolonged. 

 Histologists have appreciated the force of this argument 

 and have proposed words to denote more precisely the 

 features under di-.cii--.ion. What we have generally called 

 the nerve-cell may better be called the />< r/l.-iirifon, which 

 means specifically "around the nucleus." When we 

 adopt this we find ourselves in need of a word for the 

 combination of pcrikaryon, dendrites, and axoii (or 

 axon-.i in short, for the nerve-cell in the best sense. 

 The word supplied is neuron. 



The Neuron Theory. It is now time to outline the 

 conception of the anatomy and physiology of the nervous 

 system which for twenty-five years has been the founda- 

 tion of most presentations of these subjects. To do this 

 will be, in part, to restate what has gone before, but we 

 shall be led also to fresh considerations. The ideas to be 

 explained are not to be received as surely demonstrated, 

 but they have probably not seriously misled students in 

 the past, however they may have to be modified in the 

 future. New views are now urged by many skilled in- 

 \e-tigators anc l we must 11( ,t ignore them. Nevertheless, 

 the traditional picture of the nervous elements and their 

 relationships remains convenient for teaching and diagram- 

 matic purposes. 



The neuron theory M uines thai I he whole system is 

 capable of resolution into highly speciali/ed cells of the 

 nature already indicated. These neurons are said to be 

 "concatenated," which means enchained. The indi- 

 vidual neuron is commonly supposed not to be continuous 

 with any of its fellows, but it is supposed to affect and to 

 be affected by t hem through synapses. The valve action 

 empha-i/ed above gives each neuron a certain regularity 

 of performance; it can receive stimuli at certain points, but 

 it cannot communicate them at the same places. So also 



